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Group coded recording

April 11, 2024

In computer science, group coded recording or group code recording (GCR) refers to several distinct but related encoding methods for representing data on magnetic media. The first, used in 6250 bpi magnetic tape since 1973, is an error-correcting code combined with a run-length limited (RLL) encoding scheme, belonging into the group of modulation codes.[1] The others are different mainframe hard disk as well as floppy disk encoding methods used in some microcomputers until the late 1980s. GCR is a modified form of a NRZI code, but necessarily with a higher transition density.[1]

Magnetic tape edit

Group coded recording was first used for magnetic-tape data storage on 9-track reel-to-reel tape.[1] The term was coined during the development of the IBM 3420 Model 4/6/8 Magnetic Tape Unit[2] and the corresponding 3803 Model 2 Tape Control Unit,[3][2] both introduced in 1973.[2][4] IBM referred to the error correcting code itself as "group coded recording". However, GCR has come to refer to the recording format of 6250 bpi (250 bits/mm[1]) tape as a whole, and later to formats which use similar RLL codes without the error correction code.

In order to reliably read and write to magnetic tape, several constraints on the signal to be written must be followed. The first is that two adjacent flux reversals must be separated by a certain distance on the media, defined by the magnetic properties of the media itself. The second is that there must be a reversal often enough to keep the reader's clock in phase with the written signal; that is, the signal must be self-clocking and most importantly to keep the playback output high enough as this is proportional to the density of flux transitions. Prior to 6250 bpi tapes, 1600 bpi tapes satisfied these constraints using a technique called phase encoding (PE), which was only 50% efficient. For 6250 bpi GCR tapes, a (0, 2) RLL code is used, or more specifically a 4/5 (0, 2) block code[1] sometimes also referred to as GCR (4B-5B) encoding.[5] This code requires five bits to be written for every four bits of data.[1] The code is structured so that no more than two zero bits (which are represented by lack of a flux reversal) can occur in a row,[1] either within a code or between codes, no matter what the data was. This RLL code is applied independently to the data going to each of the nine tracks.

Of the 32 five-bit patterns, eight begin with two consecutive zero bits, six others end with two consecutive zero bits, and one more (10001) contains three consecutive zero bits. Removing the all-ones pattern (11111) from the remainder leaves 16 suitable code words.

The 6250 bpi GCR RLL code:[6][7][8][5]

4-bit value GCR code[6][7]
hex bin bin hex
0x0 0000 1.1001 0x19
0x1 0001 1.1011 0x1B
0x2 0010 1.0010 0x12
0x3 0011 1.0011 0x13
0x4 0100 1.1101 0x1D
0x5 0101 1.0101 0x15
0x6 0110 1.0110 0x16
0x7 0111 1.0111 0x17
4-bit value GCR code[6][7]
hex bin bin hex
0x8 1000 1.1010 0x1A
0x9 1001 0.1001 0x09
0xA 1010 0.1010 0x0A
0xB 1011 0.1011 0x0B
0xC 1100 1.1110 0x1E
0xD 1101 0.1101 0x0D
0xE 1110 0.1110 0x0E
0xF 1111 0.1111 0x0F

11 of the nibbles (other than xx00 and 0001) have their code formed by prepending the complement of the most significant bit; i.e. abcd is encoded as aabcd. The other five values are assigned codes beginning with 11. Nibbles of the form ab00 have codes 11baa, i.e. the bit reverse of the code for ab11. The code 0001 is assigned the remaining value 11011.

Because of the back then extremely high density of 6250 bpi tape, the RLL code is not sufficient to ensure reliable data storage. On top of the RLL code, an error-correcting code called the Optimal Rectangular Code (ORC) is applied.[9] This code is a combination of a parity track and polynomial code similar to a CRC, but structured for error correction rather than error detection. For every seven bytes written to the tape (before RLL encoding), an eighth check byte is calculated and written to the tape. When reading, the parity is calculated on each byte and exclusive-ORed with the contents of the parity track, and the polynomial check code calculated and exclusive-ORed with the received check code, resulting in two 8-bit syndrome words. If these are both zero, the data is error free. Otherwise, error-correction logic in the tape controller corrects the data before it is forwarded to the host. The error correcting code is able to correct any number of errors in any single track, or in any two tracks if the erroneous tracks can be identified by other means.

In newer IBM half-inch 18-track tape drives recording at 24000 bpi, 4/5 (0, 2) GCR was replaced by a more efficient 8/9 (0, 3) modulation code, mapping eight bits to nine bits.[1]

Hard disks edit

In the mid-1970s, Sperry Univac, ISS Division was working on large hard drives for the mainframe business using group coding.[10]

Floppy disks edit

Like magnetic tape drives, floppy disk drives have physical limits on the spacing of flux reversals (also called transitions, represented by one-bits).

Micropolis edit

Offering GCR-compatible diskette drives and floppy disk controllers (like the 100163-51-8 and 100163-52-6[11]), Micropolis endorsed data encoding with group coded recording[12] on 5¼-inch 100 tpi 77-track diskette drives to store twelve 512-byte sectors per track since 1977 or 1978.[13][14][15][16]

Micro Peripherals edit

Micro Peripherals, Inc. (MPI) marketed double-density 5¼-inch disk drives (like the single-sided B51 and double-sided B52 drives) and a controller solution implementing GCR since early 1978.[17][18]

Durango edit

The Durango Systems F-85 (introduced in September 1978[19][20]) used single-sided 5¼-inch 100 tpi diskette drives providing 480 KB utilizing a proprietary high-density 4/5 group coded encoding. The machine was using a Western Digital FD1781 floppy disk controller, designed by a former Sperry ISS engineer,[16] with 77-track Micropolis drives.[21] In later models such as the Durango 800[22] series this was expanded to a double-sided option for 960 KB (946 KB formatted[22][nb 1]) per diskette.[20][23][21][13]

Apple edit

For the Apple II floppy drive, Steve Wozniak invented a floppy controller which (along with the Disk II drive itself) imposed two constraints:

  • Between any two one bits, there may be a maximum of one zero bit.
  • Each 8-bit byte must start with a one bit.

The simplest scheme to ensure compliance with these limits is to record an extra "clock" transition before each data bit according to differential Manchester encoding or (digital) FM (Frequency Modulation). Known as 4-and-4 encoding, the resulting Apple implementation allowed only ten 256-byte sectors per track to be recorded on a single-density 5¼-inch floppy. It uses two bytes for each byte.

Close to a month prior to the shipment of the disk drive in spring 1978,[25] Wozniak realized that a more complex encoding scheme would allow each eight-bit byte on disk to hold five bits of useful data rather than four bits. This is because there are 34 bytes which have the top bit set and no two zero bits in a row. This encoding scheme became known as 5-and-3 encoding, and allowed 13 sectors per track; it was used for Apple DOS 3.1, 3.2, and 3.2.1, as well as for the earliest version of Apple CP/M [de]:[26]

Reserved GCR-codes: 0xAA and 0xD5.[26]

Wozniak called the system "my most incredible experience at Apple and the finest job I did".[25]

Later, the design of the floppy drive controller was modified to allow a byte on disk to contain up to one pair of zero bits in a row. This allowed each eight-bit byte to hold six bits of useful data, and allowed 16 sectors per track. This scheme is known as 6-and-2 encoding,[26] and was used on Apple Pascal, Apple DOS 3.3[26] and ProDOS,[28] and later with Apple FileWare drives in the Apple Lisa and the 400K and 800K 3½-inch disks on the Macintosh and Apple II.[29][30] Apple did not originally call this scheme "GCR", but the term was later applied to it[30] to distinguish it from IBM PC floppies which used the MFM encoding scheme.

Reserved GCR-codes: 0xAA and 0xD5.[26][28]

Commodore edit

Independently, Commodore Business Machines (CBM) created a group coded recording scheme for their Commodore 2040 floppy disk drive (launched in the spring of 1979). The relevant constraints on the 2040 drive were that no more than two zero bits could occur in a row; the drive imposed no special constraint on the first bit in a byte. This allowed the use of a scheme similar to that used in 6250 bpi tape drives. Every four bits of data are translated into five bits on disk, according to the following table:

4-bit value GCR code[31]
hex bin bin hex
0x0 0000 0.1010 0x0A
0x1 0001 0.1011 0x0B
0x2 0010 1.0010 0x12
0x3 0011 1.0011 0x13
0x4 0100 0.1110 0x0E
0x5 0101 0.1111 0x0F
0x6 0110 1.0110 0x16
0x7 0111 1.0111 0x17
4-bit value GCR code[31]
hex bin bin hex
0x8 1000 0.1001 0x09
0x9 1001 1.1001 0x19
0xA 1010 1.1010 0x1A
0xB 1011 1.1011 0x1B
0xC 1100 0.1101 0x0D
0xD 1101 1.1101 0x1D
0xE 1110 1.1110 0x1E
0xF 1111 1.0101 0x15

Each code starts and ends with at most one zero bit, ensuring that even when the codes are concatenated, the encoded data will never contain more than two zero bits in a row. With this encoding at most eight one bits in a row are possible. Therefore, Commodore used sequences of ten or more one bits in a row as synchronization mark.

This more efficient GCR scheme, combined with an approach at constant bit-density recording by gradually increasing the clock rate (zone constant angular velocity, ZCAV) and storing more physical sectors on the outer tracks than on the inner ones (zone bit recording, ZBR), enabled Commodore to fit 170 kB on a standard single-sided single-density 5.25-inch floppy, where Apple fit 140 kB (with 6-and-2 encoding) or 114 kB (with 5-and-3 encoding) and an FM-encoded floppy held only 88 kB.

Sirius/Victor edit

Similar, the 5.25-inch floppy drives of the Victor 9000 aka Sirius 1, designed by Chuck Peddle in 1981/1982, used a combination of ten-bit GCR and constant bit-density recording by gradually decreasing a drive's rotational speed for the outer tracks in nine zones (a form of zoned constant linear velocity (ZCLV)) while increasing the number of sectors per track (a variant of zone bit recording (ZBR)) to achieve formatted capacities of 606 kB (single sided) / 1188 kB (double-sided) on 96 tpi media.[32][33][34][35]

Brother edit

Starting around 1985, Brother introduced a family of dedicated word processor typewriters with integrated 3.5-inch 38-track[nb 2] diskette drive. Early models of the WP and LW series [de] used a Brother-specific group-coded recording scheme with twelve 256-byte sectors to store up to 120 KB[nb 3] on single-sided and up to 240 KB[nb 3] on double-sided double-density (DD) diskettes.[16][36][37][38] Reportedly, prototypes were already shown at the Internationale Funkausstellung 1979 (IFA) in Berlin.

Sharp edit

In 1986, Sharp introduced a turnable 2.5-inch pocket disk drive solution (drives: CE-1600F, CE-140F; internally based on the FDU-250 chassis; media: CE-1650F) for their series of pocket computers with a formatted capacity of 62464 bytes per side (2× 64 kB nominal, 16 tracks, 8 sectors/track, 512 bytes per sector, 48 tpi, 250 kbit/s, 270 rpm) with GCR (4/5) recording.[39][40]

Other uses edit

GCR was also evaluated for a possible use in bar code encoding schemes (packing efficiency, timing tolerances, amount of storage bytes for timing information, and DC output level).[41]

See also edit

Notes edit

  1. ^ The product flyer for the Durango 800 series documents a formatted "on-line capacity" of 1.892 MB for the diskette drives. The system, however, was equipped with two 5¼-inch Micropolis 100 tpi 77-track floppy drives by default, and 1.892 MB is about twice as large as the physical drive capacity documented in various other sources (480 KB per side), therefore, by "on-line capacity" they must have meant the available storage capacity available to users for the combination of two drives.
  2. ^ The sources give slightly contradicting parameters regarding the Brother diskette formats. 12 sectors á 256 bytes would give 120 KB per side on a 40-track drive, but one source claims the drives were 38-track only.
  3. ^ a b The following Brother models are known to support a 120 KB diskette format (incomplete list): WP-1 (1985/1987), WP-5 (1987/1989), WP-6 (1989), WP-55 (1987/1989), WP-500 (1987/1989). The following models are known to support a 240 KB format (incomplete list): WP-70, WP-75 (1989), WP-80 (1985/1989), WP-3400, WP-3410, WP-3550, WP-3650D, WP-760D, WP-760D+, LW-1 (1989), LW-20, LW-30, LW-100, LW-400.

References edit

  1. ^ a b c d e f g h Patel, Arvind Motibhai (1988). "5. Signal and Error-Control Coding". In Mee, C. Denis; Daniel, Eric D. (eds.). Magnetic Recording. Vol. II: Computer Data Storage (1st ed.). McGraw-Hill Book Company. ISBN 0-07-041272-3.
  2. ^ a b c CW staff (1973-03-14). "6,250 Byte/In. Density - IBM 3420 Storage More Than Tripled". Computerworld. VII (11). White Plains, New York, USA: 1–2. Retrieved 2017-03-23. IBM added three new models to the 3420 magnetic tape system than can record data at the "densest recording capability yet offered", according to the company. Using a new method called Group Coded Recording (GCR), the IBM drives can handle tapes containing a data density of 6,250 byte/in. compared with 1,600 byte/in. on earlier models of the 3420. […] An upgraded control unit was also announced - the 3803 Model 2 - which operates with both the earlier and latest 3420 tape units. The Model 2 includes the capability of correcting errors in one or two tracks "simultaneously while the tape is in motion", IBM said. […] The GCR method segments data written on tape into groups of characters to which a special coding character is added. And the higher density is based on a combination of a modified coding scheme, a smaller interrecord gap (called an interblock gap) and modified electronics and electromechanical components, IBM said. Installed 3803/3420 tape systems can be converted to the higher densities in the field. […]
  3. ^ . 2004. Archived from the original on 2008-12-25. […] I moved to the lab at Poughkeepsie in 1958 […] I later was Lead designer and architect for the 2802 Tape Control Unit and a few years after that, Lead Designer and Architect of the 3803 which was a very large modification based on the 2802. Three of us shared a Corporate Award for the 3803 and I, along with Planner Charlie Von Reyn, came up with the name "Group Coded Recording (GCR)" as the name of the recording method. […] (NB. An anonymous comment by one of the developers on the origin of the name "Group Coded Recording".)
  4. ^ Harris, John P.; Phillips, William B.; Wells, Jack F.; Winger, Wayne D. (September 1981). "Innovations in the Design of Magnetic Tape Subsystems". IBM Journal of Research and Development. 25 (5). International Business Machines Corporation: 691–700. CiteSeerX 10.1.1.83.2700. doi:10.1147/rd.255.0691.
  5. ^ a b Geffroy, Jean-Claude; Motet, Gilles (2013-03-09) [2002]. "15.12 Exercise GCR (4B - 5B) code". Design of Dependable Computing Systems. Toulouse, France: Springer Science+Business Media, B.V. / Kluwer Academic Publishers. pp. 426, 591. ISBN 978-1-4020-0437-7. LCCN 2002-284974. ISBN 94-015-9884-3. Retrieved 2021-11-18. (672 pages)
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  10. ^ Jacoby, George V. (2003-01-06) [September 1977]. "A new look-ahead code for increased data density". IEEE Transactions on Magnetics. 13 (5). Sperry Univac, ISS Division, Cupertino, CA, USA: IEEE: 1202–1204. doi:10.1109/TMAG.1977.1059670. (NB. This article about the 3PM code was also presented at the Intermag 1977 in June 1977.)
  11. ^ "Micropolis 100163 Intelligent Controller". Micropolis. Retrieved 2022-06-26.)
  12. ^ US 4261019, McClelland, S. Barry, "Compatible Digital Magnetic Recording System", published 1981-04-07, assigned to Micropolis Corporation  (NB. Application Number: US 06/098381)
  13. ^ a b "NCC Preview: OEMs at NCC - Micropolis Corp". Computerworld. XII (22). CW Communications, Inc.: P/50. 1978-05-28. Retrieved 2017-06-12. […] Micropolis has extended the capacity of 5.25-in. floppy disk subsystems via double-sided models with formatted file storage of up to nearly 2 million bytes […] The Megafloppy series also features an intelligent controller that facilitates interconnection of four subsystems to a common host interface for a total on-line storage capacity of more than 15M bytes […] Double-sided versions of the product line will be implemented first in two OEM series - Model 1015 and Model 1055 […] The Model 1015 is an unpackaged drive designed for the manufacturer who integrates floppy disk storage into his own system enclosure. A range of storage capacities from 143,000 to 630,000 bytes per drive is available […] Model 1015 customers have the option of using the Micropolis intelligent controller and Group Code Recording (GCR) method to further expand file space up to 946,000 bytes […] Offering GCR and a microprocessor-based controller as standard features, the Model 1055 5.25-in. floppy has four soft-sectored formats for each of its 77 tracks, yielding a maximum capacity of 1,892,000 bytes of file space on its double-sided version […] An add-on module available for the 1055 is comprised of two read/write heads and two drives, sharing a common controller. The subsystem capacity (formatted) with the module is 3,784,000 bytes […] Up to four 1055s, each with an add-on module, can be daisy-chained to a common host for a maximum on-line storage capacity of more than 15M bytes […]
  14. ^ Micropolis Maintenance Manual Floppy Disk Subsystem (PDF) (revision 1, 1st ed.). Micropolis Corporation. February 1979. 1082-04. (PDF) from the original on 2017-06-12. Retrieved 2017-06-12. (NB. Micropolis 100163-51-8 and 100163-52-6 are GCR-based.)
  15. ^ "InfoNews/Hardware: Hardware/Briefs". InfoWorld. 2 (2): 19. 1980-03-03. Retrieved 2017-06-12. […] Four new 96 tracks-per-inch products have been added to Micropolis' current line of 100 tpi single-sided and double-sided floppy disks. The 96 tpi drives offer 70 tracks-per-side, as opposed to the 77 offered by the MegaFloppy line. The four models are: 1) The 1015-V: 436 KB, unformatted, FM/MFM recording […] 2) The 1016-V: 532 KB unformatted, Group Coded Recording (GCR) […] 3) The 1015-VI: a two-head version of the MFM drive, 872 KB […] 4) The 1016-VI: also a two-head drive, 1.064 MB GCR encoding […]
  16. ^ a b c Guzis, Charles "Chuck" P. (2015-09-20). "Multi-platform distribution format". Sydex. from the original on 2017-06-14. Retrieved 2017-06-14. […] At the same time Micropolis was working a 5.25" drive that could hold about as much as an 8", using some tricks. The Micropolis drive was 100 tpi, 77 track and, by using GCR, could hold 12 512-byte sectors per track. That's 462 KiB. This was about 1977-78. […] The […] drive and controller implementation (ours was done by a guy we'd recruited from Sperry ISS) was […] complex and expensive […] Brother WP disks […] are 38 track, single-sided, Brother-encoded GCR that hold […] 120K on 2D floppies. […]
  17. ^ Allen, David (February 1978). (PDF). BYTE. 3 (2). Kansas City, USA: 114, 116–118, 120, 122, 134–125. Archived from the original (PDF) on 2017-06-14. Retrieved 2017-06-14. […] Of the alternative codes used to achieve double density, GCR (Group Coded Recording) looks quite attractive. Micro Peripherals Inc has implemented double density using GCR in a full size floppy disk and controller system currently being marketed. […] GCR is nothing more than the old standby NRZ with its attendant advantages, but, since ordinary NRZ has no clocking information and a potentially high DC content during long strings of ones or zeros, the data is reformatted to eliminate the long strings. The reformatting converts each four bit group of original data into five bits of group coded data; the five bits in the encoded version will always have a mix of ones and zeros, even if the real data is all in one state. Reformatting in GCR can be accomplished in software, as opposed to MFM, etc, which almost unavoidably must be encoded and decoded in hardware. Thus, GCR has good possibilities as a low cost, high reliability scheme for achieving double density. […][1]
  18. ^ "Floppies Claim Improved Performance". Computerworld. XIII (7). CW Communications, Inc.: 90. 1979-02-12. Retrieved 2017-06-14.
  19. ^ Schultz, Brad (1978-10-02). "Business Mini Weighs 65 Pound - What is Durango?". Computerworld. XII (40). CW Communications, Inc.: 1, 4. Retrieved 2017-06-13.
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  21. ^ a b Guzis, Charles "Chuck" P. (2009-09-13). "Durango GCR". Sydex. from the original on 2017-11-04. Retrieved 2017-03-25.
  22. ^ a b "800 Technical Summary - 800 Series Business Computer System" (PDF). San Jose, CA, USA: Durango Systems, Inc. (PDF) from the original on 2017-03-23. Retrieved 2017-03-23.
  23. ^ Guzis, Charles "Chuck" P. (October 2006). "The Durango F-85 Computer". Sydex. from the original on 2017-03-23. Retrieved 2017-03-23.
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  25. ^ a b Williams, Gregg; Moore, Rob (January 1985). . BYTE (interview): 166. Archived from the original on 2012-02-12. Retrieved 2013-10-26. [2] (NB. Interview with Steve Wozniak, where he describes creating the Apple version of GCR.)
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  29. ^ a b c d e Feichtinger, Herwig (1987). Arbeitsbuch Mikrocomputer (in German) (2 ed.). Munich, Germany: Franzis-Verlag GmbH. pp. 223–224. ISBN 3-7723-8022-0.
  30. ^ a b Apple Computer, Inc. (February 1982) [1978]. Integrated Woz Machine (IWM) Specification (PDF) (19 ed.). DigiBarn Computer Museum. (PDF) from the original on 2016-08-06. Retrieved 2016-08-06.
  31. ^ a b Hildon, Karl J. H. (March 1985). "GCR codes". The Complete Commodore Inner Space Anthology (PDF). Milton, Ontario, Canada: Transactor Publishing Incorporated. p. 49. ISBN 0-9692086-0-X. (PDF) from the original on 2017-03-23. Retrieved 2017-03-23. [7] (NB. Commodore GCR codes—but this reference erroneously claims that a 1-bit indicates a lack of a transition.)
  32. ^ "Victor 9000/Sirius 1 Specification" (PDF). commodore.ca. (PDF) from the original on 2017-03-23. Retrieved 2017-03-23.
  33. ^ "Supplemental Technical Reference Material". Revision 0 (1st printing ed.). Scotts Valley, CA, USA: Victor Publications. 1983-03-23. Application Note: 002. […] Single-sided floppy drive offers 80 tracks at 96 TPI […] Double-sided floppy drive offers 160 tracks at 96 TPI […] Floppy drives have 512 byte sectors; utilising a GCR, 10-bit recording technique. […] Although the Victor 9000 uses 5 1/4-inch minifloppies of a similar type to those used in other computers, the floppy disks themselves are not readable on other machines, nor can the Victor 9000 read a disk from another manufacturers machine. The Victor 9000 uses a unique recording method to allow the data to be packed as densely as 600 kbytes on a single-sided single-density minifloppy; this recording method involves the regulation of the speed at which the floppy rotates, explaining the fact that the noise from the drive sometimes changes frequency.
  34. ^ "Chapter 7. Disk Drive Assembly". Victor 9000 Technical Reference Manual (PDF). Victor Business Products, Inc. June 1982. pp. 7–1..7–9. 710620. (PDF) from the original on 2017-03-23. Retrieved 2017-03-23. […] Track density is 96 tracks per inch, and recording density is maintained at approximately 8000 bits per inch on all tracks. […] The VICTOR 9000 uses an encoding technique called group code recording (GCR) to convert the data from internal representation to an acceptable form. GCR converts each (4-bit) nibble into a 5-bit code that guarantees a recording pattern that never has more than two zeros together. Then data is recorded on the disk by causing a flux reversal for each "one" bit and no flux reversal for each "zero" bit. […]
  35. ^ Sargent III., Murray; Shoemaker, Richard L.; Stelzer, Ernst H. K. (1988). Assemblersprache und Hardware des IBM PC/XT/AT (in German) (1 ed.). Addison-Wesley Verlag (Deutschland) GmbH / Addison-Wesley Publishing Company. ISBN 3-89319-110-0. . VVA-Nr. 563-00110-4.
  36. ^ Gieseke, Hans-Werner (2003-08-27). "Brother WP-1" (in German). from the original on 2017-06-14. Retrieved 2017-06-14. (NB. Reportedly, the Brother WP-1 technical data was derived from page 109 of the user manual.)
  37. ^ French, Mick (2002-09-13). . Archived from the original on 2017-11-22. Retrieved 2017-06-14. […] The 3.5" 240Kb disk drive is a single head Brother part no.13194989 and is connected with a 15 pin ribbon. […] it initializes (formats) the disk to a capacity of 236.5Kb. […]
  38. ^ Cotgrove, Michael S. (2009-02-26). "archaic floppy disc format". Retrieved 2017-06-14. […] There were several 3.5" Brother disks that are completely nonstandard. […] One had 1296 byte sectors and another had 12 x 256 byte GCR sectors […]
  39. ^ "Model CE-1600F". Sharp PC-1600 Service Manual (PDF). Yamatokoriyama, Japan: Sharp Corporation, Information Systems Group, Quality & Reliability Control Center. July 1986. pp. 98–104. (PDF) from the original on 2017-05-07. Retrieved 2017-03-23. GCR is an abbreviation of Group Coded Recording. A single byte, 8 bits, data are divided into two 4-bit data which is also converted onto a 5-bit data. Thus, a single byte (8 bits) is recorded on the media as a 10-bit data.
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Further reading edit

  • ANSI INCITS 40-1993 (R2003) Unrecorded Magnetic Tape for Information Interchange (9-track, 800 bpi, NRZI; 1600 bpi, PE; and 6250 bpi, GCR)
  • ANSI INCITS 54-1986 (R2002) Recorded Magnetic Tape for Information Interchange (6250 bpi, GCR)
  • Sallet, Herbert W. (July 1977). "Magnetic tape: A high performer: Magnetic tape has evolved into a highly effective medium for high-density and low-cost-per-bit data recording". IEEE Spectrum. 14 (7): 26–31. doi:10.1109/MSPEC.1977.6501525.
  • Sidhu, Pawitter S. (December 1976). "Group-Coded Recording Reliably Doubles Diskette Capacity". Computer Design: 84–88.
  • "(unknown)". Perkin-Elmer Data Systems News. Perkin-Elmer Data Systems. 1977-06-14. {{cite journal}}: Cite uses generic title (help)
  • Hsiao, (Ben) M. Y.; Carter, William C.; Thomas, James W.; Stringfellow, William R. (September 1981). "Reliability, Availability, and Serviceability of IBM Computer Systems". IBM Journal of Research and Development. 25 (5): 462. doi:10.1147/rd.255.0453. (NB. Mentions the 5/4 RLL code used on 6250 bpi tape drives.)
  • (PDF) (Revision J ed.). Canoga Park, CA, USA: Qualstar Corporation. pp. 3-4..3-7. 500450. Archived from the original (PDF) on 2011-09-30. Retrieved 2017-03-23. (NB. Additional detail on the GCR tape format.)
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  • Dickreiter, Michael; Dittel, Volker; Hoeg, Wolfgang; Wöhr, Martin (2014). Handbuch der Tonstudiotechnik (in German). Walter de Gruyter GmbH & Co KG. ISBN 978-3-11031650-6. ISBN 3-11031650-1. Retrieved 2018-07-09.
  • Bergmans, Jan W. M. (2013-03-09) [1996]. "Chapter 4.8.3 Group-Coded Recording (GCR) Code". Digital Baseband Transmission and Recording (reprint ed.). Philips Research, Eindhoven, Netherlands: Kluwer Academic Publishers / Springer Science & Business Media. doi:10.1007/978-1-4757-2471-4. ISBN 978-1-4419-5164-9. Retrieved 2018-07-09.
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External links edit

  • "Les Disquettes Et Le Drive Disk II" (in French). from the original on 2018-07-09. Retrieved 2018-07-09., "Les Nibbles" (in French). from the original on 2017-03-22. Retrieved 2018-07-09., "La Methode PRODOS: Rapide Et Efficace" (in French). from the original on 2018-07-09. Retrieved 2018-07-09.

April 11, 2024
group, coded, recording, computer, science, group, coded, recording, group, code, recording, refers, several, distinct, related, encoding, methods, representing, data, magnetic, media, first, used, 6250, magnetic, tape, since, 1973, error, correcting, code, co. In computer science group coded recording or group code recording GCR refers to several distinct but related encoding methods for representing data on magnetic media The first used in 6250 bpi magnetic tape since 1973 is an error correcting code combined with a run length limited RLL encoding scheme belonging into the group of modulation codes 1 The others are different mainframe hard disk as well as floppy disk encoding methods used in some microcomputers until the late 1980s GCR is a modified form of a NRZI code but necessarily with a higher transition density 1 Contents 1 Magnetic tape 2 Hard disks 3 Floppy disks 3 1 Micropolis 3 2 Micro Peripherals 3 3 Durango 3 4 Apple 3 5 Commodore 3 6 Sirius Victor 3 7 Brother 3 8 Sharp 4 Other uses 5 See also 6 Notes 7 References 8 Further reading 9 External linksMagnetic tape editGroup coded recording was first used for magnetic tape data storage on 9 track reel to reel tape 1 The term was coined during the development of the IBM 3420 Model 4 6 8 Magnetic Tape Unit 2 and the corresponding 3803 Model 2 Tape Control Unit 3 2 both introduced in 1973 2 4 IBM referred to the error correcting code itself as group coded recording However GCR has come to refer to the recording format of 6250 bpi 250 bits mm 1 tape as a whole and later to formats which use similar RLL codes without the error correction code In order to reliably read and write to magnetic tape several constraints on the signal to be written must be followed The first is that two adjacent flux reversals must be separated by a certain distance on the media defined by the magnetic properties of the media itself The second is that there must be a reversal often enough to keep the reader s clock in phase with the written signal that is the signal must be self clocking and most importantly to keep the playback output high enough as this is proportional to the density of flux transitions Prior to 6250 bpi tapes 1600 bpi tapes satisfied these constraints using a technique called phase encoding PE which was only 50 efficient For 6250 bpi GCR tapes a 0 2 RLL code is used or more specifically a 4 5 0 2 block code 1 sometimes also referred to as GCR 4B 5B encoding 5 This code requires five bits to be written for every four bits of data 1 The code is structured so that no more than two zero bits which are represented by lack of a flux reversal can occur in a row 1 either within a code or between codes no matter what the data was This RLL code is applied independently to the data going to each of the nine tracks Of the 32 five bit patterns eight begin with two consecutive zero bits six others end with two consecutive zero bits and one more 10001 contains three consecutive zero bits Removing the all ones pattern 11111 from the remainder leaves 16 suitable code words The 6250 bpi GCR RLL code 6 7 8 5 4 bit value GCR code 6 7 hex bin bin hex0x0 0000 1 1001 0x190x1 0001 1 1011 0x1B0x2 0010 1 0010 0x120x3 0011 1 0011 0x130x4 0100 1 1101 0x1D0x5 0101 1 0101 0x150x6 0110 1 0110 0x160x7 0111 1 0111 0x17 4 bit value GCR code 6 7 hex bin bin hex0x8 1000 1 1010 0x1A0x9 1001 0 1001 0x090xA 1010 0 1010 0x0A0xB 1011 0 1011 0x0B0xC 1100 1 1110 0x1E0xD 1101 0 1101 0x0D0xE 1110 0 1110 0x0E0xF 1111 0 1111 0x0F11 of the nibbles other than xx00 and 0001 have their code formed by prepending the complement of the most significant bit i e abcd is encoded as a abcd The other five values are assigned codes beginning with 11 Nibbles of the form ab00 have codes 11baa i e the bit reverse of the code for ab11 The code 0001 is assigned the remaining value 11011 Because of the back then extremely high density of 6250 bpi tape the RLL code is not sufficient to ensure reliable data storage On top of the RLL code an error correcting code called the Optimal Rectangular Code ORC is applied 9 This code is a combination of a parity track and polynomial code similar to a CRC but structured for error correction rather than error detection For every seven bytes written to the tape before RLL encoding an eighth check byte is calculated and written to the tape When reading the parity is calculated on each byte and exclusive ORed with the contents of the parity track and the polynomial check code calculated and exclusive ORed with the received check code resulting in two 8 bit syndrome words If these are both zero the data is error free Otherwise error correction logic in the tape controller corrects the data before it is forwarded to the host The error correcting code is able to correct any number of errors in any single track or in any two tracks if the erroneous tracks can be identified by other means In newer IBM half inch 18 track tape drives recording at 24000 bpi 4 5 0 2 GCR was replaced by a more efficient 8 9 0 3 modulation code mapping eight bits to nine bits 1 Hard disks editIn the mid 1970s Sperry Univac ISS Division was working on large hard drives for the mainframe business using group coding 10 Floppy disks editLike magnetic tape drives floppy disk drives have physical limits on the spacing of flux reversals also called transitions represented by one bits Micropolis edit Offering GCR compatible diskette drives and floppy disk controllers like the 100163 51 8 and 100163 52 6 11 Micropolis endorsed data encoding with group coded recording 12 on 5 inch 100 tpi 77 track diskette drives to store twelve 512 byte sectors per track since 1977 or 1978 13 14 15 16 Micro Peripherals edit Micro Peripherals Inc MPI marketed double density 5 inch disk drives like the single sided B51 and double sided B52 drives and a controller solution implementing GCR since early 1978 17 18 Durango edit The Durango Systems F 85 introduced in September 1978 19 20 used single sided 5 inch 100 tpi diskette drives providing 480 KB utilizing a proprietary high density 4 5 group coded encoding The machine was using a Western Digital FD1781 floppy disk controller designed by a former Sperry ISS engineer 16 with 77 track Micropolis drives 21 In later models such as the Durango 800 22 series this was expanded to a double sided option for 960 KB 946 KB formatted 22 nb 1 per diskette 20 23 21 13 Apple edit For the Apple II floppy drive Steve Wozniak invented a floppy controller which along with the Disk II drive itself imposed two constraints Between any two one bits there may be a maximum of one zero bit Each 8 bit byte must start with a one bit The simplest scheme to ensure compliance with these limits is to record an extra clock transition before each data bit according to differential Manchester encoding or digital FM Frequency Modulation Known as 4 and 4 encoding the resulting Apple implementation allowed only ten 256 byte sectors per track to be recorded on a single density 5 inch floppy It uses two bytes for each byte 4 and 4 encoding table Value Code 24 hex bin bin hex0x00 0000 0000 1010 1010 1010 1010 0xAA 0xAA0x01 0000 0001 1010 1010 1010 1011 0xAA 0xAB0x02 0000 0010 1010 1011 1010 1010 0xAB 0xAA0x03 0000 0011 1010 1011 1010 1011 0xAB 0xAB0x04 0000 0100 1010 1010 1010 1110 0xAA 0xAE0x05 0000 0101 1010 1010 1010 1111 0xAA 0xAF0x06 0000 0110 1010 1011 1010 1110 0xAB 0xAE0x07 0000 0111 1010 1011 1010 1111 0xAB 0xAF0x08 0000 1000 1010 1110 1010 1010 0xAE 0xAA0x09 0000 1001 1010 1110 1010 1011 0xAE 0xAB0x0A 0000 1010 1010 1111 1010 1010 0xAF 0xAA0x0B 0000 1011 1010 1111 1010 1011 0xAF 0xAB0x0C 0000 1100 1010 1110 1010 1110 0xAE 0xAE0x0D 0000 1101 1010 1110 1010 1111 0xAE 0xAF0x0E 0000 1110 1010 1111 1010 1110 0xAF 0xAE0x0F 0000 1111 1010 1111 1010 1111 0xAF 0xAF0x10 0001 0000 1010 1010 1011 1010 0xAA 0xBA0x11 0001 0001 1010 1010 1011 1011 0xAA 0xBB0x12 0001 0010 1010 1011 1011 1010 0xAB 0xBA0x13 0001 0011 1010 1011 1011 1011 0xAB 0xBB0x14 0001 0100 1010 1010 1011 1110 0xAA 0xBE0x15 0001 0101 1010 1010 1011 1111 0xAA 0xBF0x16 0001 0110 1010 1011 1011 1110 0xAB 0xBE0x17 0001 0111 1010 1011 1011 1111 0xAB 0xBF0x18 0001 1000 1010 1110 1011 1010 0xAE 0xBA0x19 0001 1001 1010 1110 1011 1011 0xAE 0xBB0x1A 0001 1010 1010 1111 1011 1010 0xAF 0xBA0x1B 0001 1011 1010 1111 1011 1011 0xAF 0xBB0x1C 0001 1100 1010 1110 1011 1110 0xAE 0xBE0x1D 0001 1101 1010 1110 1011 1111 0xAE 0xBF0x1E 0001 1110 1010 1111 1011 1110 0xAF 0xBE0x1F 0001 1111 1010 1111 1011 1111 0xAF 0xBF0x20 0010 0000 1011 1010 1010 1010 0xBA 0xAA0x21 0010 0001 1011 1010 1010 1011 0xBA 0xAB0x22 0010 0010 1011 1011 1010 1010 0xBB 0xAA0x23 0010 0011 1011 1011 1010 1011 0xBB 0xAB0x24 0010 0100 1011 1010 1010 1110 0xBA 0xAE0x25 0010 0101 1011 1010 1010 1111 0xBA 0xAF0x26 0010 0110 1011 1011 1010 1110 0xBB 0xAE0x27 0010 0111 1011 1011 1010 1111 0xBB 0xAF0x28 0010 1000 1011 1110 1010 1010 0xBE 0xAA0x29 0010 1001 1011 1110 1010 1011 0xBE 0xAB0x2A 0010 1010 1011 1111 1010 1010 0xBF 0xAA0x2B 0010 1011 1011 1111 1010 1011 0xBF 0xAB0x2C 0010 1100 1011 1110 1010 1110 0xBE 0xAE0x2D 0010 1101 1011 1110 1010 1111 0xBE 0xAF0x2E 0010 1110 1011 1111 1010 1110 0xBF 0xAE0x2F 0010 1111 1011 1111 1010 1111 0xBF 0xAF0x30 0011 0000 1011 1010 1011 1010 0xBA 0xBA0x31 0011 0001 1011 1010 1011 1011 0xBA 0xBB0x32 0011 0010 1011 1011 1011 1010 0xBB 0xBA0x33 0011 0011 1011 1011 1011 1011 0xBB 0xBB0x34 0011 0100 1011 1010 1011 1110 0xBA 0xBE0x35 0011 0101 1011 1010 1011 1111 0xBA 0xBF0x36 0011 0110 1011 1011 1011 1110 0xBB 0xBE0x37 0011 0111 1011 1011 1011 1111 0xBB 0xBF0x38 0011 1000 1011 1110 1011 1010 0xBE 0xBA0x39 0011 1001 1011 1110 1011 1011 0xBE 0xBB0x3A 0011 1010 1011 1111 1011 1010 0xBF 0xBA0x3B 0011 1011 1011 1111 1011 1011 0xBF 0xBB0x3C 0011 1100 1011 1110 1011 1110 0xBE 0xBE0x3D 0011 1101 1011 1110 1011 1111 0xBE 0xBF0x3E 0011 1110 1011 1111 1011 1110 0xBF 0xBE0x3F 0011 1111 1011 1111 1011 1111 0xBF 0xBF Value Code 24 hex bin bin hex0x40 0100 0000 1010 1010 1110 1010 0xAA 0xEA0x41 0100 0001 1010 1010 1110 1011 0xAA 0xEB0x42 0100 0010 1010 1011 1110 1010 0xAB 0xEA0x43 0100 0011 1010 1011 1110 1011 0xAB 0xEB0x44 0100 0100 1010 1010 1110 1110 0xAA 0xEE0x45 0100 0101 1010 1010 1110 1111 0xAA 0xEF0x46 0100 0110 1010 1011 1110 1110 0xAB 0xEE0x47 0100 0111 1010 1011 1110 1111 0xAB 0xEF0x48 0100 1000 1010 1110 1110 1010 0xAE 0xEA0x49 0100 1001 1010 1110 1110 1011 0xAE 0xEB0x4A 0100 1010 1010 1111 1110 1010 0xAF 0xEA0x4B 0100 1011 1010 1111 1110 1011 0xAF 0xEB0x4C 0100 1100 1010 1110 1110 1110 0xAE 0xEE0x4D 0100 1101 1010 1110 1110 1111 0xAE 0xEF0x4E 0100 1110 1010 1111 1110 1110 0xAF 0xEE0x4F 0100 1111 1010 1111 1110 1111 0xAF 0xEF0x50 0101 0000 1010 1010 1111 1010 0xAA 0xFA0x51 0101 0001 1010 1010 1111 1011 0xAA 0xFB0x52 0101 0010 1010 1011 1111 1010 0xAB 0xFA0x53 0101 0011 1010 1011 1111 1011 0xAB 0xFB0x54 0101 0100 1010 1010 1111 1110 0xAA 0xFE0x55 0101 0101 1010 1010 1111 1111 0xAA 0xFF0x56 0101 0110 1010 1011 1111 1110 0xAB 0xFE0x57 0101 0111 1010 1011 1111 1111 0xAB 0xFF0x58 0101 1000 1010 1110 1111 1010 0xAE 0xFA0x59 0101 1001 1010 1110 1111 1011 0xAE 0xFB0x5A 0101 1010 1010 1111 1111 1010 0xAF 0xFA0x5B 0101 1011 1010 1111 1111 1011 0xAF 0xFB0x5C 0101 1100 1010 1110 1111 1110 0xAE 0xFE0x5D 0101 1101 1010 1110 1111 1111 0xAE 0xFF0x5E 0101 1110 1010 1111 1111 1110 0xAF 0xFE0x5F 0101 1111 1010 1111 1111 1111 0xAF 0xFF0x60 0110 0000 1011 1010 1110 1010 0xBA 0xEA0x61 0110 0001 1011 1010 1110 1011 0xBA 0xEB0x62 0110 0010 1011 1011 1110 1010 0xBB 0xEA0x63 0110 0011 1011 1011 1110 1011 0xBB 0xEB0x64 0110 0100 1011 1010 1110 1110 0xBA 0xEE0x65 0110 0101 1011 1010 1110 1111 0xBA 0xEF0x66 0110 0110 1011 1011 1110 1110 0xBB 0xEE0x67 0110 0111 1011 1011 1110 1111 0xBB 0xEF0x68 0110 1000 1011 1110 1110 1010 0xBE 0xEA0x69 0110 1001 1011 1110 1110 1011 0xBE 0xEB0x6A 0110 1010 1011 1111 1110 1010 0xBF 0xEA0x6B 0110 1011 1011 1111 1110 1011 0xBF 0xEB0x6C 0110 1100 1011 1110 1110 1110 0xBE 0xEE0x6D 0110 1101 1011 1110 1110 1111 0xBE 0xEF0x6E 0110 1110 1011 1111 1110 1110 0xBF 0xEE0x6F 0110 1111 1011 1111 1110 1111 0xBF 0xEF0x70 0111 0000 1011 1010 1111 1010 0xBA 0xFA0x71 0111 0001 1011 1010 1111 1011 0xBA 0xFB0x72 0111 0010 1011 1011 1111 1010 0xBB 0xFA0x73 0111 0011 1011 1011 1111 1011 0xBB 0xFB0x74 0111 0100 1011 1010 1111 1110 0xBA 0xFE0x75 0111 0101 1011 1010 1111 1111 0xBA 0xFF0x76 0111 0110 1011 1011 1111 1110 0xBB 0xFE0x77 0111 0111 1011 1011 1111 1111 0xBB 0xFF0x78 0111 1000 1011 1110 1111 1010 0xBE 0xFA0x79 0111 1001 1011 1110 1111 1011 0xBE 0xFB0x7A 0111 1010 1011 1111 1111 1010 0xBF 0xFA0x7B 0111 1011 1011 1111 1111 1011 0xBF 0xFB0x7C 0111 1100 1011 1110 1111 1110 0xBE 0xFE0x7D 0111 1101 1011 1110 1111 1111 0xBE 0xFF0x7E 0111 1110 1011 1111 1111 1110 0xBF 0xFE0x7F 0111 1111 1011 1111 1111 1111 0xBF 0xFF Value Code 24 hex bin bin hex0x80 1000 0000 1110 1010 1010 1010 0xEA 0xAA0x81 1000 0001 1110 1010 1010 1011 0xEA 0xAB0x82 1000 0010 1110 1011 1010 1010 0xEB 0xAA0x83 1000 0011 1110 1011 1010 1011 0xEB 0xAB0x84 1000 0100 1110 1010 1010 1110 0xEA 0xAE0x85 1000 0101 1110 1010 1010 1111 0xEA 0xAF0x86 1000 0110 1110 1011 1010 1110 0xEB 0xAE0x87 1000 0111 1110 1011 1010 1111 0xEB 0xAF0x88 1000 1000 1110 1110 1010 1010 0xEE 0xAA0x89 1000 1001 1110 1110 1010 1011 0xEE 0xAB0x8A 1000 1010 1110 1111 1010 1010 0xEF 0xAA0x8B 1000 1011 1110 1111 1010 1011 0xEF 0xAB0x8C 1000 1100 1110 1110 1010 1110 0xEE 0xAE0x8D 1000 1101 1110 1110 1010 1111 0xEE 0xAF0x8E 1000 1110 1110 1111 1010 1110 0xEF 0xAE0x8F 1000 1111 1110 1111 1010 1111 0xEF 0xAF0x90 1001 0000 1110 1010 1011 1010 0xEA 0xBA0x91 1001 0001 1110 1010 1011 1011 0xEA 0xBB0x92 1001 0010 1110 1011 1011 1010 0xEB 0xBA0x93 1001 0011 1110 1011 1011 1011 0xEB 0xBB0x94 1001 0100 1110 1010 1011 1110 0xEA 0xBE0x95 1001 0101 1110 1010 1011 1111 0xEA 0xBF0x96 1001 0110 1110 1011 1011 1110 0xEB 0xBE0x97 1001 0111 1110 1011 1011 1111 0xEB 0xBF0x98 1001 1000 1110 1110 1011 1010 0xEE 0xBA0x99 1001 1001 1110 1110 1011 1011 0xEE 0xBB0x9A 1001 1010 1110 1111 1011 1010 0xEF 0xBA0x9B 1001 1011 1110 1111 1011 1011 0xEF 0xBB0x9C 1001 1100 1110 1110 1011 1110 0xEE 0xBE0x9D 1001 1101 1110 1110 1011 1111 0xEE 0xBF0x9E 1001 1110 1110 1111 1011 1110 0xEF 0xBE0x9F 1001 1111 1110 1111 1011 1111 0xEF 0xBF0xA0 1010 0000 1111 1010 1010 1010 0xFA 0xAA0xA1 1010 0001 1111 1010 1010 1011 0xFA 0xAB0xA2 1010 0010 1111 1011 1010 1010 0xFB 0xAA0xA3 1010 0011 1111 1011 1010 1011 0xFB 0xAB0xA4 1010 0100 1111 1010 1010 1110 0xFA 0xAE0xA5 1010 0101 1111 1010 1010 1111 0xFA 0xAF0xA6 1010 0110 1111 1011 1010 1110 0xFB 0xAE0xA7 1010 0111 1111 1011 1010 1111 0xFB 0xAF0xA8 1010 1000 1111 1110 1010 1010 0xFE 0xAA0xA9 1010 1001 1111 1110 1010 1011 0xFE 0xAB0xAA 1010 1010 1111 1111 1010 1010 0xFF 0xAA0xAB 1010 1011 1111 1111 1010 1011 0xFF 0xAB0xAC 1010 1100 1111 1110 1010 1110 0xFE 0xAE0xAD 1010 1101 1111 1110 1010 1111 0xFE 0xAF0xAE 1010 1110 1111 1111 1010 1110 0xFF 0xAE0xAF 1010 1111 1111 1111 1010 1111 0xFF 0xAF0xB0 1011 0000 1111 1010 1011 1010 0xFA 0xBA0xB1 1011 0001 1111 1010 1011 1011 0xFA 0xBB0xB2 1011 0010 1111 1011 1011 1010 0xFB 0xBA0xB3 1011 0011 1111 1011 1011 1011 0xFB 0xBB0xB4 1011 0100 1111 1010 1011 1110 0xFA 0xBE0xB5 1011 0101 1111 1010 1011 1111 0xFA 0xBF0xB6 1011 0110 1111 1011 1011 1110 0xFB 0xBE0xB7 1011 0111 1111 1011 1011 1111 0xFB 0xBF0xB8 1011 1000 1111 1110 1011 1010 0xFE 0xBA0xB9 1011 1001 1111 1110 1011 1011 0xFE 0xBB0xBA 1011 1010 1111 1111 1011 1010 0xFF 0xBA0xBB 1011 1011 1111 1111 1011 1011 0xFF 0xBB0xBC 1011 1100 1111 1110 1011 1110 0xFE 0xBE0xBD 1011 1101 1111 1110 1011 1111 0xFE 0xBF0xBE 1011 1110 1111 1111 1011 1110 0xFF 0xBE0xBF 1011 1111 1111 1111 1011 1111 0xFF 0xBF Value Code 24 hex bin bin hex0xC0 1100 0000 1110 1010 1110 1010 0xEA 0xEA0xC1 1100 0001 1110 1010 1110 1011 0xEA 0xEB0xC2 1100 0010 1110 1011 1110 1010 0xEB 0xEA0xC3 1100 0011 1110 1011 1110 1011 0xEB 0xEB0xC4 1100 0100 1110 1010 1110 1110 0xEA 0xEE0xC5 1100 0101 1110 1010 1110 1111 0xEA 0xEF0xC6 1100 0110 1110 1011 1110 1110 0xEB 0xEE0xC7 1100 0111 1110 1011 1110 1111 0xEB 0xEF0xC8 1100 1000 1110 1110 1110 1010 0xEE 0xEA0xC9 1100 1001 1110 1110 1110 1011 0xEE 0xEB0xCA 1100 1010 1110 1111 1110 1010 0xEF 0xEA0xCB 1100 1011 1110 1111 1110 1011 0xEF 0xEB0xCC 1100 1100 1110 1110 1110 1110 0xEE 0xEE0xCD 1100 1101 1110 1110 1110 1111 0xEE 0xEF0xCE 1100 1110 1110 1111 1110 1110 0xEF 0xEE0xCF 1100 1111 1110 1111 1110 1111 0xEF 0xEF0xD0 1101 0000 1110 1010 1111 1010 0xEA 0xFA0xD1 1101 0001 1110 1010 1111 1011 0xEA 0xFB0xD2 1101 0010 1110 1011 1111 1010 0xEB 0xFA0xD3 1101 0011 1110 1011 1111 1011 0xEB 0xFB0xD4 1101 0100 1110 1010 1111 1110 0xEA 0xFE0xD5 1101 0101 1110 1010 1111 1111 0xEA 0xFF0xD6 1101 0110 1110 1011 1111 1110 0xEB 0xFE0xD7 1101 0111 1110 1011 1111 1111 0xEB 0xFF0xD8 1101 1000 1110 1110 1111 1010 0xEE 0xFA0xD9 1101 1001 1110 1110 1111 1011 0xEE 0xFB0xDA 1101 1010 1110 1111 1111 1010 0xEF 0xFA0xDB 1101 1011 1110 1111 1111 1011 0xEF 0xFB0xDC 1101 1100 1110 1110 1111 1110 0xEE 0xFE0xDD 1101 1101 1110 1110 1111 1111 0xEE 0xFF0xDE 1101 1110 1110 1111 1111 1110 0xEF 0xFE0xDF 1101 1111 1110 1111 1111 1111 0xEF 0xFF0xE0 1110 0000 1111 1010 1110 1010 0xFA 0xEA0xE1 1110 0001 1111 1010 1110 1011 0xFA 0xEB0xE2 1110 0010 1111 1011 1110 1010 0xFB 0xEA0xE3 1110 0011 1111 1011 1110 1011 0xFB 0xEB0xE4 1110 0100 1111 1010 1110 1110 0xFA 0xEE0xE5 1110 0101 1111 1010 1110 1111 0xFA 0xEF0xE6 1110 0110 1111 1011 1110 1110 0xFB 0xEE0xE7 1110 0111 1111 1011 1110 1111 0xFB 0xEF0xE8 1110 1000 1111 1110 1110 1010 0xFE 0xEA0xE9 1110 1001 1111 1110 1110 1011 0xFE 0xEB0xEA 1110 1010 1111 1111 1110 1010 0xFF 0xEA0xEB 1110 1011 1111 1111 1110 1011 0xFF 0xEB0xEC 1110 1100 1111 1110 1110 1110 0xFE 0xEE0xED 1110 1101 1111 1110 1110 1111 0xFE 0xEF0xEE 1110 1110 1111 1111 1110 1110 0xFF 0xEE0xEF 1110 1111 1111 1111 1110 1111 0xFF 0xEF0xF0 1111 0000 1111 1010 1111 1010 0xFA 0xFA0xF1 1111 0001 1111 1010 1111 1011 0xFA 0xFB0xF2 1111 0010 1111 1011 1111 1010 0xFB 0xFA0xF3 1111 0011 1111 1011 1111 1011 0xFB 0xFB0xF4 1111 0100 1111 1010 1111 1110 0xFA 0xFE0xF5 1111 0101 1111 1010 1111 1111 0xFA 0xFF0xF6 1111 0110 1111 1011 1111 1110 0xFB 0xFE0xF7 1111 0111 1111 1011 1111 1111 0xFB 0xFF0xF8 1111 1000 1111 1110 1111 1010 0xFE 0xFA0xF9 1111 1001 1111 1110 1111 1011 0xFE 0xFB0xFA 1111 1010 1111 1111 1111 1010 0xFF 0xFA0xFB 1111 1011 1111 1111 1111 1011 0xFF 0xFB0xFC 1111 1100 1111 1110 1111 1110 0xFE 0xFE0xFD 1111 1101 1111 1110 1111 1111 0xFE 0xFF0xFE 1111 1110 1111 1111 1111 1110 0xFF 0xFE0xFF 1111 1111 1111 1111 1111 1111 0xFF 0xFF Close to a month prior to the shipment of the disk drive in spring 1978 25 Wozniak realized that a more complex encoding scheme would allow each eight bit byte on disk to hold five bits of useful data rather than four bits This is because there are 34 bytes which have the top bit set and no two zero bits in a row This encoding scheme became known as 5 and 3 encoding and allowed 13 sectors per track it was used for Apple DOS 3 1 3 2 and 3 2 1 as well as for the earliest version of Apple CP M de 26 5 and 3 encoding table 5 bit value GCR code 26 27 hex bin bin hex0x00 0 0000 1010 1011 0xAB0x01 0 0001 1010 1101 0xAD0x02 0 0010 1010 1110 0xAE0x03 0 0011 1010 1111 0xAF0x04 0 0100 1011 0101 0xB50x05 0 0101 1011 0110 0xB60x06 0 0110 1011 0111 0xB70x07 0 0111 1011 1010 0xBA0x08 0 1000 1011 1011 0xBB0x09 0 1001 1011 1101 0xBD0x0A 0 1010 1011 1110 0xBE0x0B 0 1011 1011 1111 0xBF0x0C 0 1100 1101 0110 0xD60x0D 0 1101 1101 0111 0xD70x0E 0 1110 1101 1010 0xDA0x0F 0 1111 1101 1011 0xDB 5 bit value GCR code 26 27 hex bin bin hex0x10 1 0000 1101 1101 0xDD0x11 1 0001 1101 1110 0xDE0x12 1 0010 1101 1111 0xDF0x13 1 0011 1110 1010 0xEA0x14 1 0100 1110 1011 0xEB0x15 1 0101 1110 1101 0xED0x16 1 0110 1110 1110 0xEE0x17 1 0111 1110 1111 0xEF0x18 1 1000 1111 0101 0xF50x19 1 1001 1111 0110 0xF60x1A 1 1010 1111 0111 0xF70x1B 1 1011 1111 1010 0xFA0x1C 1 1100 1111 1011 0xFB0x1D 1 1101 1111 1101 0xFD0x1E 1 1110 1111 1110 0xFE0x1F 1 1111 1111 1111 0xFF Reserved GCR codes 0xAA and 0xD5 26 Wozniak called the system my most incredible experience at Apple and the finest job I did 25 Later the design of the floppy drive controller was modified to allow a byte on disk to contain up to one pair of zero bits in a row This allowed each eight bit byte to hold six bits of useful data and allowed 16 sectors per track This scheme is known as 6 and 2 encoding 26 and was used on Apple Pascal Apple DOS 3 3 26 and ProDOS 28 and later with Apple FileWare drives in the Apple Lisa and the 400K and 800K 3 inch disks on the Macintosh and Apple II 29 30 Apple did not originally call this scheme GCR but the term was later applied to it 30 to distinguish it from IBM PC floppies which used the MFM encoding scheme 6 and 2 encoding table 6 bit value GCR code 29 26 28 27 24 hex bin bin hex0x00 00 0000 1001 0110 0x960x01 00 0001 1001 0111 0x970x02 00 0010 1001 1010 0x9A0x03 00 0011 1001 1011 0x9B0x04 00 0100 1001 1101 0x9D0x05 00 0101 1001 1110 0x9E0x06 00 0110 1001 1111 0x9F0x07 00 0111 1010 0110 0xA60x08 00 1000 1010 0111 0xA70x09 00 1001 1010 1011 0xAB0x0A 00 1010 1010 1100 0xAC0x0B 00 1011 1010 1101 0xAD0x0C 00 1100 1010 1110 0xAE0x0D 00 1101 1010 1111 0xAF0x0E 00 1110 1011 0010 0xB20x0F 00 1111 1011 0011 0xB3 6 bit value GCR code 29 26 28 27 24 hex bin bin hex0x10 01 0000 1011 0100 0xB40x11 01 0001 1011 0101 0xB50x12 01 0010 1011 0110 0xB60x13 01 0011 1011 0111 0xB70x14 01 0100 1011 1001 0xB90x15 01 0101 1011 1010 0xBA0x16 01 0110 1011 1011 0xBB0x17 01 0111 1011 1100 0xBC0x18 01 1000 1011 1101 0xBD0x19 01 1001 1011 1110 0xBE0x1A 01 1010 1011 1111 0xBF0x1B 01 1011 1100 1011 0xCB0x1C 01 1100 1100 1101 0xCD0x1D 01 1101 1100 1110 0xCE0x1E 01 1110 1100 1111 0xCF0x1F 01 1111 1101 0011 0xD3 6 bit value GCR code 29 26 28 27 24 hex bin bin hex0x20 10 0000 1101 0110 0xD60x21 10 0001 1101 0111 0xD70x22 10 0010 1101 1001 0xD90x23 10 0011 1101 1010 0xDA0x24 10 0100 1101 1011 0xDB0x25 10 0101 1101 1100 0xDC0x26 10 0110 1101 1101 0xDD0x27 10 0111 1101 1110 0xDE0x28 10 1000 1101 1111 0xDF0x29 10 1001 1110 0101 0xE50x2A 10 1010 1110 0110 0xE60x2B 10 1011 1110 0111 0xE70x2C 10 1100 1110 1001 0xE90x2D 10 1101 1110 1010 0xEA0x2E 10 1110 1110 1011 0xEB0x2F 10 1111 1110 1100 0xEC 6 bit value GCR code 29 26 28 27 24 hex bin bin hex0x30 11 0000 1110 1101 0xED0x31 11 0001 1110 1110 0xEE0x32 11 0010 1110 1111 0xEF0x33 11 0011 1111 0010 0xF20x34 11 0100 1111 0011 0xF30x35 11 0101 1111 0100 0xF40x36 11 0110 1111 0101 0xF50x37 11 0111 1111 0110 0xF60x38 11 1000 1111 0111 0xF70x39 11 1001 1111 1001 0xF90x3A 11 1010 1111 1010 0xFA0x3B 11 1011 1111 1011 0xFB0x3C 11 1100 1111 1100 0xFC0x3D 11 1101 1111 1101 0xFD0x3E 11 1110 1111 1110 0xFE0x3F 11 1111 1111 1111 0xFF Reserved GCR codes 0xAA and 0xD5 26 28 Commodore edit Independently Commodore Business Machines CBM created a group coded recording scheme for their Commodore 2040 floppy disk drive launched in the spring of 1979 The relevant constraints on the 2040 drive were that no more than two zero bits could occur in a row the drive imposed no special constraint on the first bit in a byte This allowed the use of a scheme similar to that used in 6250 bpi tape drives Every four bits of data are translated into five bits on disk according to the following table 4 bit value GCR code 31 hex bin bin hex0x0 0000 0 1010 0x0A0x1 0001 0 1011 0x0B0x2 0010 1 0010 0x120x3 0011 1 0011 0x130x4 0100 0 1110 0x0E0x5 0101 0 1111 0x0F0x6 0110 1 0110 0x160x7 0111 1 0111 0x17 4 bit value GCR code 31 hex bin bin hex0x8 1000 0 1001 0x090x9 1001 1 1001 0x190xA 1010 1 1010 0x1A0xB 1011 1 1011 0x1B0xC 1100 0 1101 0x0D0xD 1101 1 1101 0x1D0xE 1110 1 1110 0x1E0xF 1111 1 0101 0x15Each code starts and ends with at most one zero bit ensuring that even when the codes are concatenated the encoded data will never contain more than two zero bits in a row With this encoding at most eight one bits in a row are possible Therefore Commodore used sequences of ten or more one bits in a row as synchronization mark This more efficient GCR scheme combined with an approach at constant bit density recording by gradually increasing the clock rate zone constant angular velocity ZCAV and storing more physical sectors on the outer tracks than on the inner ones zone bit recording ZBR enabled Commodore to fit 170 kB on a standard single sided single density 5 25 inch floppy where Apple fit 140 kB with 6 and 2 encoding or 114 kB with 5 and 3 encoding and an FM encoded floppy held only 88 kB Sirius Victor edit Similar the 5 25 inch floppy drives of the Victor 9000 aka Sirius 1 designed by Chuck Peddle in 1981 1982 used a combination of ten bit GCR and constant bit density recording by gradually decreasing a drive s rotational speed for the outer tracks in nine zones a form of zoned constant linear velocity ZCLV while increasing the number of sectors per track a variant of zone bit recording ZBR to achieve formatted capacities of 606 kB single sided 1188 kB double sided on 96 tpi media 32 33 34 35 Brother edit Starting around 1985 Brother introduced a family of dedicated word processor typewriters with integrated 3 5 inch 38 track nb 2 diskette drive Early models of the WP and LW series de used a Brother specific group coded recording scheme with twelve 256 byte sectors to store up to 120 KB nb 3 on single sided and up to 240 KB nb 3 on double sided double density DD diskettes 16 36 37 38 Reportedly prototypes were already shown at the Internationale Funkausstellung 1979 IFA in Berlin Sharp edit In 1986 Sharp introduced a turnable 2 5 inch pocket disk drive solution drives CE 1600F CE 140F internally based on the FDU 250 chassis media CE 1650F for their series of pocket computers with a formatted capacity of 62464 bytes per side 2 64 kB nominal 16 tracks 8 sectors track 512 bytes per sector 48 tpi 250 kbit s 270 rpm with GCR 4 5 recording 39 40 Other uses editGCR was also evaluated for a possible use in bar code encoding schemes packing efficiency timing tolerances amount of storage bytes for timing information and DC output level 41 See also editModified Frequency Modulation MFM Run Length Limited RLL Eight to Fourteen Modulation EFM Error correcting code 8b 10b encoding Group code 4B5B Integrated Woz Machine IWM a GCR disk controller in Apple computers Paula MOS Technology 8364 a GCR capable disk controller in Commodore Amiga computers Individual Computers Catweasel a special diskette controller able to read some GCR formats KryoFlux a special diskette controller able to read some GCR formats Notes edit The product flyer for the Durango 800 series documents a formatted on line capacity of 1 892 MB for the diskette drives The system however was equipped with two 5 inch Micropolis 100 tpi 77 track floppy drives by default and 1 892 MB is about twice as large as the physical drive capacity documented in various other sources 480 KB per side therefore by on line capacity they must have meant the available storage capacity available to users for the combination of two drives The sources give slightly contradicting parameters regarding the Brother diskette formats 12 sectors a 256 bytes would give 120 KB per side on a 40 track drive but one source claims the drives were 38 track only a b The following Brother models are known to support a 120 KB diskette format incomplete list WP 1 1985 1987 WP 5 1987 1989 WP 6 1989 WP 55 1987 1989 WP 500 1987 1989 The following models are known to support a 240 KB format incomplete list WP 70 WP 75 1989 WP 80 1985 1989 WP 3400 WP 3410 WP 3550 WP 3650D WP 760D WP 760D LW 1 1989 LW 20 LW 30 LW 100 LW 400 References edit a b c d e f g h Patel Arvind Motibhai 1988 5 Signal and Error Control Coding In Mee C Denis Daniel Eric D eds Magnetic Recording Vol II Computer Data Storage 1st ed McGraw Hill Book Company ISBN 0 07 041272 3 a b c CW staff 1973 03 14 6 250 Byte In Density IBM 3420 Storage More Than Tripled Computerworld VII 11 White Plains New York USA 1 2 Retrieved 2017 03 23 IBM added three new models to the 3420 magnetic tape system than can record data at the densest recording capability yet offered according to the company Using a new method called Group Coded Recording GCR the IBM drives can handle tapes containing a data density of 6 250 byte in compared with 1 600 byte in on earlier models of the 3420 An upgraded control unit was also announced the 3803 Model 2 which operates with both the earlier and latest 3420 tape units The Model 2 includes the capability of correcting errors in one or two tracks simultaneously while the tape is in motion IBM said The GCR method segments data written on tape into groups of characters to which a special coding character is added And the higher density is based on a combination of a modified coding scheme a smaller interrecord gap called an interblock gap and modified electronics and electromechanical components IBM said Installed 3803 3420 tape systems can be converted to the higher densities in the field The Gallery of Old Iron 2004 Archived from the original on 2008 12 25 I moved to the lab at Poughkeepsie in 1958 I later was Lead designer and architect for the 2802 Tape Control Unit and a few years after that Lead Designer and Architect of the 3803 which was a very large modification based on the 2802 Three of us shared a Corporate Award for the 3803 and I along with Planner Charlie Von Reyn came up with the name Group Coded Recording GCR as the name of the recording method NB An anonymous comment by one of the developers on the origin of the name Group Coded Recording Harris John P Phillips William B Wells Jack F Winger Wayne D September 1981 Innovations in the Design of Magnetic Tape Subsystems IBM Journal of Research and Development 25 5 International Business Machines Corporation 691 700 CiteSeerX 10 1 1 83 2700 doi 10 1147 rd 255 0691 a b Geffroy Jean Claude Motet Gilles 2013 03 09 2002 15 12 Exercise GCR 4B 5B code Design of Dependable Computing Systems Toulouse France Springer Science Business Media B V Kluwer Academic Publishers pp 426 591 ISBN 978 1 4020 0437 7 LCCN 2002 284974 ISBN 94 015 9884 3 Retrieved 2021 11 18 672 pages a b c Keong Kwoh Chee Computer Peripherals PDF School of Computer Engineering Nanyang Technological University Singapore Chapter 7 Magnetic Recording Fundamentals archived PDF from the original on 2017 03 23 retrieved 2017 03 23 a b c Watkinson John 1990 3 4 Group codes Coding for Digital Recording Stoneham MA USA Focal Press pp 51 61 ISBN 0 240 51293 6 Savard John J G 2018 2006 Digital Magnetic Tape Recording quadibloc Archived from the original on 2018 07 02 Retrieved 2018 07 16 Patel Arvind Motibhai Hong Se June 1974 Optimal Rectangular Code for High Density Magnetic Tapes IBM Journal of Research and Development 18 6 579 588 doi 10 1147 rd 186 0579 Archived from the original on 2017 11 04 Retrieved 2017 03 21 Jacoby George V 2003 01 06 September 1977 A new look ahead code for increased data density IEEE Transactions on Magnetics 13 5 Sperry Univac ISS Division Cupertino CA USA IEEE 1202 1204 doi 10 1109 TMAG 1977 1059670 NB This article about the 3PM code was also presented at the Intermag 1977 in June 1977 Micropolis 100163 Intelligent Controller Micropolis Retrieved 2022 06 26 US 4261019 McClelland S Barry Compatible Digital Magnetic Recording System published 1981 04 07 assigned to Micropolis Corporation NB Application Number US 06 098381 a b NCC Preview OEMs at NCC Micropolis Corp Computerworld XII 22 CW Communications Inc P 50 1978 05 28 Retrieved 2017 06 12 Micropolis has extended the capacity of 5 25 in floppy disk subsystems via double sided models with formatted file storage of up to nearly 2 million bytes The Megafloppy series also features an intelligent controller that facilitates interconnection of four subsystems to a common host interface for a total on line storage capacity of more than 15M bytes Double sided versions of the product line will be implemented first in two OEM series Model 1015 and Model 1055 The Model 1015 is an unpackaged drive designed for the manufacturer who integrates floppy disk storage into his own system enclosure A range of storage capacities from 143 000 to 630 000 bytes per drive is available Model 1015 customers have the option of using the Micropolis intelligent controller and Group Code Recording GCR method to further expand file space up to 946 000 bytes Offering GCR and a microprocessor based controller as standard features the Model 1055 5 25 in floppy has four soft sectored formats for each of its 77 tracks yielding a maximum capacity of 1 892 000 bytes of file space on its double sided version An add on module available for the 1055 is comprised of two read write heads and two drives sharing a common controller The subsystem capacity formatted with the module is 3 784 000 bytes Up to four 1055s each with an add on module can be daisy chained to a common host for a maximum on line storage capacity of more than 15M bytes Micropolis Maintenance Manual Floppy Disk Subsystem PDF revision 1 1st ed Micropolis Corporation February 1979 1082 04 Archived PDF from the original on 2017 06 12 Retrieved 2017 06 12 NB Micropolis 100163 51 8 and 100163 52 6 are GCR based InfoNews Hardware Hardware Briefs InfoWorld 2 2 19 1980 03 03 Retrieved 2017 06 12 Four new 96 tracks per inch products have been added to Micropolis current line of 100 tpi single sided and double sided floppy disks The 96 tpi drives offer 70 tracks per side as opposed to the 77 offered by the MegaFloppy line The four models are 1 The 1015 V 436 KB unformatted FM MFM recording 2 The 1016 V 532 KB unformatted Group Coded Recording GCR 3 The 1015 VI a two head version of the MFM drive 872 KB 4 The 1016 VI also a two head drive 1 064 MB GCR encoding a b c Guzis Charles Chuck P 2015 09 20 Multi platform distribution format Sydex Archived from the original on 2017 06 14 Retrieved 2017 06 14 At the same time Micropolis was working a 5 25 drive that could hold about as much as an 8 using some tricks The Micropolis drive was 100 tpi 77 track and by using GCR could hold 12 512 byte sectors per track That s 462 KiB This was about 1977 78 The drive and controller implementation ours was done by a guy we d recruited from Sperry ISS was complex and expensive Brother WP disks are 38 track single sided Brother encoded GCR that hold 120K on 2D floppies Allen David February 1978 A Minifloppy Interface PDF BYTE 3 2 Kansas City USA 114 116 118 120 122 134 125 Archived from the original PDF on 2017 06 14 Retrieved 2017 06 14 Of the alternative codes used to achieve double density GCR Group Coded Recording looks quite attractive Micro Peripherals Inc has implemented double density using GCR in a full size floppy disk and controller system currently being marketed GCR is nothing more than the old standby NRZ with its attendant advantages but since ordinary NRZ has no clocking information and a potentially high DC content during long strings of ones or zeros the data is reformatted to eliminate the long strings The reformatting converts each four bit group of original data into five bits of group coded data the five bits in the encoded version will always have a mix of ones and zeros even if the real data is all in one state Reformatting in GCR can be accomplished in software as opposed to MFM etc which almost unavoidably must be encoded and decoded in hardware Thus GCR has good possibilities as a low cost high reliability scheme for achieving double density 1 Floppies Claim Improved Performance Computerworld XIII 7 CW Communications Inc 90 1979 02 12 Retrieved 2017 06 14 Schultz Brad 1978 10 02 Business Mini Weighs 65 Pound What is Durango Computerworld XII 40 CW Communications Inc 1 4 Retrieved 2017 06 13 a b Comstock George E 2003 08 13 Oral History of George Comstock PDF Interviewed by Hendrie Gardner Mountain View California USA Computer History Museum CHM X2727 2004 Archived PDF from the original on 2017 03 23 Retrieved 2017 03 23 a b Guzis Charles Chuck P 2009 09 13 Durango GCR Sydex Archived from the original on 2017 11 04 Retrieved 2017 03 25 a b 800 Technical Summary 800 Series Business Computer System PDF San Jose CA USA Durango Systems Inc Archived PDF from the original on 2017 03 23 Retrieved 2017 03 23 Guzis Charles Chuck P October 2006 The Durango F 85 Computer Sydex Archived from the original on 2017 03 23 Retrieved 2017 03 23 a b c d e f g h Copy II Plus Version 9 ProDOS DOS Utilities Data Recovery File Management Protected Software Backup PDF 9 0 Central Point Software Inc 1989 10 31 1982 Archived from the original PDF on 2017 05 07 Retrieved 2017 03 21 a b Williams Gregg Moore Rob January 1985 The Apple Story Part 2 More History and the Apple III BYTE interview 166 Archived from the original on 2012 02 12 Retrieved 2013 10 26 2 NB Interview with Steve Wozniak where he describes creating the Apple version of GCR a b c d e f g h i j k Worth Don D Lechner Pieter M May 1982 1981 Beneath Apple DOS 4th printing ed Reseda CA USA Quality Software Retrieved 2017 03 21 3 4 5 Archived 9 March 2016 at the Wayback Machine a b c d e f Sather James Fielding 1983 Understanding the Apple II A Learning Guide and Hardware Manual for the Apple II Computer 1st ed Chatsworth CA USA Quality Software pp 9 26 9 27 ISBN 0 912985 01 1 Retrieved 2017 03 21 a b c d e f Worth Don D Lechner Pieter M March 1985 1984 Beneath Apple ProDOS For Users of Apple II Plus Apple IIe and Apple IIc Computers PDF 2nd printing ed Chatsworth CA USA Quality Software ISBN 0 912985 05 4 LCCN 84 61383 Archived PDF from the original on 2017 03 21 Retrieved 2017 03 21 6 a b c d e Feichtinger Herwig 1987 Arbeitsbuch Mikrocomputer in German 2 ed Munich Germany Franzis Verlag GmbH pp 223 224 ISBN 3 7723 8022 0 a b Apple Computer Inc February 1982 1978 Integrated Woz Machine IWM Specification PDF 19 ed DigiBarn Computer Museum Archived PDF from the original on 2016 08 06 Retrieved 2016 08 06 a b Hildon Karl J H March 1985 GCR codes The Complete Commodore Inner Space Anthology PDF Milton Ontario Canada Transactor Publishing Incorporated p 49 ISBN 0 9692086 0 X Archived PDF from the original on 2017 03 23 Retrieved 2017 03 23 7 NB Commodore GCR codes but this reference erroneously claims that a 1 bit indicates a lack of a transition Victor 9000 Sirius 1 Specification PDF commodore ca Archived PDF from the original on 2017 03 23 Retrieved 2017 03 23 Supplemental Technical Reference Material Revision 0 1st printing ed Scotts Valley CA USA Victor Publications 1983 03 23 Application Note 002 Single sided floppy drive offers 80 tracks at 96 TPI Double sided floppy drive offers 160 tracks at 96 TPI Floppy drives have 512 byte sectors utilising a GCR 10 bit recording technique Although the Victor 9000 uses 5 1 4 inch minifloppies of a similar type to those used in other computers the floppy disks themselves are not readable on other machines nor can the Victor 9000 read a disk from another manufacturers machine The Victor 9000 uses a unique recording method to allow the data to be packed as densely as 600 kbytes on a single sided single density minifloppy this recording method involves the regulation of the speed at which the floppy rotates explaining the fact that the noise from the drive sometimes changes frequency Chapter 7 Disk Drive Assembly Victor 9000 Technical Reference Manual PDF Victor Business Products Inc June 1982 pp 7 1 7 9 710620 Archived PDF from the original on 2017 03 23 Retrieved 2017 03 23 Track density is 96 tracks per inch and recording density is maintained at approximately 8000 bits per inch on all tracks The VICTOR 9000 uses an encoding technique called group code recording GCR to convert the data from internal representation to an acceptable form GCR converts each 4 bit nibble into a 5 bit code that guarantees a recording pattern that never has more than two zeros together Then data is recorded on the disk by causing a flux reversal for each one bit and no flux reversal for each zero bit Sargent III Murray Shoemaker Richard L Stelzer Ernst H K 1988 Assemblersprache und Hardware des IBM PC XT AT in German 1 ed Addison Wesley Verlag Deutschland GmbH Addison Wesley Publishing Company ISBN 3 89319 110 0 VVA Nr 563 00110 4 Gieseke Hans Werner 2003 08 27 Brother WP 1 in German Archived from the original on 2017 06 14 Retrieved 2017 06 14 NB Reportedly the Brother WP 1 technical data was derived from page 109 of the user manual French Mick 2002 09 13 Brother WP 6 Archived from the original on 2017 11 22 Retrieved 2017 06 14 The 3 5 240Kb disk drive is a single head Brother part no 13194989 and is connected with a 15 pin ribbon it initializes formats the disk to a capacity of 236 5Kb Cotgrove Michael S 2009 02 26 archaic floppy disc format Retrieved 2017 06 14 There were several 3 5 Brother disks that are completely nonstandard One had 1296 byte sectors and another had 12 x 256 byte GCR sectors Model CE 1600F Sharp PC 1600 Service Manual PDF Yamatokoriyama Japan Sharp Corporation Information Systems Group Quality amp Reliability Control Center July 1986 pp 98 104 Archived PDF from the original on 2017 05 07 Retrieved 2017 03 23 GCR is an abbreviation of Group Coded Recording A single byte 8 bits data are divided into two 4 bit data which is also converted onto a 5 bit data Thus a single byte 8 bits is recorded on the media as a 10 bit data Sharp Service Manual Model CE 140F Pocket Disk Drive PDF Sharp Corporation 00ZCE140F SME Archived PDF from the original on 2017 03 11 Retrieved 2017 03 11 Moseley Robin C April 1979 Technical Forum A Comparison of Bar Code Encoding Schemes PDF BYTE 4 4 Andover MA USA 50 52 Retrieved 2017 06 14 Further reading editANSI INCITS 40 1993 R2003 Unrecorded Magnetic Tape for Information Interchange 9 track 800 bpi NRZI 1600 bpi PE and 6250 bpi GCR ANSI INCITS 54 1986 R2002 Recorded Magnetic Tape for Information Interchange 6250 bpi GCR Sallet Herbert W July 1977 Magnetic tape A high performer Magnetic tape has evolved into a highly effective medium for high density and low cost per bit data recording IEEE Spectrum 14 7 26 31 doi 10 1109 MSPEC 1977 6501525 Sidhu Pawitter S December 1976 Group Coded Recording Reliably Doubles Diskette Capacity Computer Design 84 88 unknown Perkin Elmer Data Systems News Perkin Elmer Data Systems 1977 06 14 a href Template Cite journal html title Template Cite journal cite journal a Cite uses generic title help Hsiao Ben M Y Carter William C Thomas James W Stringfellow William R September 1981 Reliability Availability and Serviceability of IBM Computer Systems IBM Journal of Research and Development 25 5 462 doi 10 1147 rd 255 0453 NB Mentions the 5 4 RLL code used on 6250 bpi tape drives Qualstar 34XX Technical Service Manual PDF Revision J ed Canoga Park CA USA Qualstar Corporation pp 3 4 3 7 500450 Archived from the original PDF on 2011 09 30 Retrieved 2017 03 23 NB Additional detail on the GCR tape format US 3685033 Agrawala Ashok K amp Srivastava Keshava Block encoding for magnetic recording systems published 1972 08 15 assigned to Honeywell Inc NB Application No US 66199 See also CA993998A CA993998A1 DE2142428A1 US 4210959 Wozniak Stephen G Controller for magnetic disc recorder or the like published 1980 07 01 assigned to Apple Computer Inc NB Application Number US 5 904420 US 4564941 Woolley Richard N Glover Neal amp Williams Richard Error detection system published 1986 01 14 assigned to Apple Computer Inc NB Application Number US 06 559210 See also CA1208794A CA1208794A1 DE3443272A1 DE3443272C2 Dockery Sean Brendan Apple II disk encoding NEC µPD72070 Floppy Disk Controller Specification Version 2 0 PDF 2 0 preliminary NEC Corporation October 1991 Archived from the original PDF on 2017 03 20 Retrieved 2017 03 20 Akesson Linus 2013 03 31 GCR decoding on the fly Archived from the original on 2017 03 21 Retrieved 2017 03 21 Trikaliotis Spiro 2010 03 05 Commodore GCR mysteries Archived from the original on 2014 08 05 GCR ROM en decoder in Commodore 8050 and 8250 disk drives Forum 64 Archived from the original on 2010 03 12 Irwin John W Cassie John V Oppeboen Harlyn C September 1971 1970 12 11 The IBM 3803 3420 Magnetic Tape Subsystem IBM Journal of Research and Development IBM 391 400 CiteSeerX 10 1 1 89 7834 Docket June 2014 Milestone Proposal Introduction of the Apple Macintosh Computer 1984 Archived from the original on 2018 07 09 Retrieved 2018 07 09 Crazy Disk Encoding Schemes Big Mess O Wires BMOW Plus Too 2011 10 02 Archived from the original on 2018 07 09 Retrieved 2018 07 09 Dickreiter Michael Dittel Volker Hoeg Wolfgang Wohr Martin 2014 Handbuch der Tonstudiotechnik in German Walter de Gruyter GmbH amp Co KG ISBN 978 3 11031650 6 ISBN 3 11031650 1 Retrieved 2018 07 09 Bergmans Jan W M 2013 03 09 1996 Chapter 4 8 3 Group Coded Recording GCR Code Digital Baseband Transmission and Recording reprint ed Philips Research Eindhoven Netherlands Kluwer Academic Publishers Springer Science amp Business Media doi 10 1007 978 1 4757 2471 4 ISBN 978 1 4419 5164 9 Retrieved 2018 07 09 Camras Marvin 2012 1988 Magnetic Recording Handbook reprint ed Van Nostrand Reinhold Company Springer Science amp Business doi 10 1007 978 94 010 9468 9 ISBN 978 9 40109468 9 LCCN 86 24762 ISBN 9 40109468 3 Retrieved 2018 07 09 In Single Drive Setup Tape System Has Three Densities Computerworld XIII 19 Louisville Colorado USA CW Communications Inc 59 1979 05 07 Retrieved 2018 07 09 External links edit Les Disquettes Et Le Drive Disk II in French Archived from the original on 2018 07 09 Retrieved 2018 07 09 Les Nibbles in French Archived from the original on 2017 03 22 Retrieved 2018 07 09 La Methode PRODOS Rapide Et Efficace in French Archived from the original on 2018 07 09 Retrieved 2018 07 09 Retrieved from https en wikipedia org w index php title Group coded recording amp oldid 1215532300 5 and 3, wikipedia, wiki, book, books, library,

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