Write combining (WC)[1] is a computer bus technique for allowing data to be combined and temporarily stored in a buffer – the write combine buffer (WCB) – to be released together later in burst mode instead of writing (immediately) as single bits or small chunks.
Write combining cannot be used for general memory access (data or code regions) due to the weak ordering. Write-combining does not guarantee that the combination of writes and reads is done in the expected order. For example, a write/read/write combination to a specific address would lead to the write combining order of read/write/write which can lead to obtaining wrong values with the first read (which potentially relies on the write before).
In order to avoid the problem of read/write order described above, the write buffer can be treated as a fully associativecache and added into the memory hierarchy of the device in which it is implemented.[2] Adding complexity slows down the memory hierarchy so this technique is often only used for memory which does not need strong ordering (always correct) like the frame buffers of video cards.
^BearWindows (2008-09-01). "Video Hardware Acceleration in DOS Environment". BearWindows Vault. Retrieved 2010-11-02.
External links
6x86opt, ctppro, CTU, DirectNT, FastVid, fstorion, K6Speed, MTRRLFBE, S3 Speed Up & Write Allocate Monitor enable LFB and BVGA Write Combining on Intel Pentium Pro/2/3/4 and AMD K6 CPUs in Windows 9x, Windows NTx, DOS, OS/2 and Linux
MTRRLFBE enable LFB and BVGA Write Combining on Intel Pentium Pro/2/3/4 CPUs in Windows 9x and DOS
(Internet Archive cached copy) enable LFB and Banked VGA Write Combining on AMD K6 CPUs in Windows 9x and DOS
February 24, 2023
write, combining, this, article, needs, additional, citations, verification, please, help, improve, this, article, adding, citations, reliable, sources, unsourced, material, challenged, removed, find, sources, news, newspapers, books, scholar, jstor, april, 20. This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Write combining news newspapers books scholar JSTOR April 2012 Learn how and when to remove this template message Write combining WC 1 is a computer bus technique for allowing data to be combined and temporarily stored in a buffer the write combine buffer WCB to be released together later in burst mode instead of writing immediately as single bits or small chunks Contents 1 Technique 2 See also 3 References 4 External linksTechnique EditWrite combining cannot be used for general memory access data or code regions due to the weak ordering Write combining does not guarantee that the combination of writes and reads is done in the expected order For example a write read write combination to a specific address would lead to the write combining order of read write write which can lead to obtaining wrong values with the first read which potentially relies on the write before In order to avoid the problem of read write order described above the write buffer can be treated as a fully associative cache and added into the memory hierarchy of the device in which it is implemented 2 Adding complexity slows down the memory hierarchy so this technique is often only used for memory which does not need strong ordering always correct like the frame buffers of video cards See also EditFramebuffer FB and when linear LFB Memory type range registers MTRR the older x86 cache control mechanism Page attribute table PAT x86 page table extension that allows fine grained cache control including write combining Page table Uncacheable speculative write combining USWC Video Graphics Array VGA and Banked BVGA Frame BufferReferences Edit Intel November 1998 Write Combining Memory Implementation Guidelines PDF Intel Retrieved 2010 11 02 BearWindows 2008 09 01 Video Hardware Acceleration in DOS Environment BearWindows Vault Retrieved 2010 11 02 External links Edit6x86opt ctppro CTU DirectNT FastVid fstorion K6Speed MTRRLFBE S3 Speed Up amp Write Allocate Monitor enable LFB and BVGA Write Combining on Intel Pentium Pro 2 3 4 and AMD K6 CPUs in Windows 9x Windows NTx DOS OS 2 and Linux MTRRLFBE enable LFB and BVGA Write Combining on Intel Pentium Pro 2 3 4 CPUs in Windows 9x and DOS CTU Internet Archive cached copy enable LFB and Banked VGA Write Combining on AMD K6 CPUs in Windows 9x and DOS Retrieved from https en wikipedia org w index php title Write combining amp oldid 1021277706, wikipedia, wiki, book, books, library,
