In IBM System/360 architecture all instructions address memory by specifying a 12-bit offset (4096 bytes) from a value in a "base register" with optional indexing. Originally addresses occupied the low-order 24 bits of a base register, allowing a program to access up to 16 MB. System/370-XA extended the architecture to allow 31-bit addressing and address spaces of up to 2 GB.
Enterprise Systems Architecture/370 further expanded addressing capabilities with access registers. Sixteen 32-bit access registers "shadow" the sixteen general-purpose registers. In a processor mode called access-register mode the access register corresponding to the specified base register designates the operand address space to be accessed.[2]: 1–1 The contents of an access register is called an "Access-list entry token" (ALET), which contains an index into a system table identifying the address space.
access, register, terminology, access, register, hardware, register, later, processors, work, conjunction, with, general, purpose, registers, giving, program, transparent, access, sixteen, address, spaces, simultaneously, were, introduced, with, 1988, supporte. In IBM terminology an Access Register AR is a hardware register in ESA 370 and later processors Access registers work in conjunction with the general purpose registers giving a program transparent access to up to sixteen 2 GB address spaces simultaneously ARs were introduced with ESA 370 in 1988 and supported by the MVS ESA operating system 1 In IBM System 360 architecture all instructions address memory by specifying a 12 bit offset 4096 bytes from a value in a base register with optional indexing Originally addresses occupied the low order 24 bits of a base register allowing a program to access up to 16 MB System 370 XA extended the architecture to allow 31 bit addressing and address spaces of up to 2 GB Enterprise Systems Architecture 370 further expanded addressing capabilities with access registers Sixteen 32 bit access registers shadow the sixteen general purpose registers In a processor mode called access register mode the access register corresponding to the specified base register designates the operand address space to be accessed 2 1 1 The contents of an access register is called an Access list entry token ALET which contains an index into a system table identifying the address space See also EditAddress registerReferences Edit Babcocl Charles Feb 22 1988 IBM opens data trove to E model users Computerworld Retrieved Mar 5 2020 IBM Corporation August 1988 IBM Enterprise Systems Architecture 370 Principles of Operation PDF Retrieved Mar 6 2020 This computer storage related article is a stub You can help Wikipedia by expanding it vte This mainframe computer related article is a stub You can help Wikipedia by expanding it vte Retrieved from https en wikipedia org w index php title Access register amp oldid 1033264017, wikipedia, wiki, book, books, library,
