The Burroughs B5000 was the first
stack machine
In computer science, computer engineering and programming language implementations, a stack machine is a computer processor or a Virtual machine#Process virtual machines, process virtual machine in which the primary interaction is moving short- ...
and also the first computer with a
segmented virtual memory
In computing, virtual memory, or virtual storage, is a memory management technique that provides an "idealized abstraction of the storage resources that are actually available on a given machine" which "creates the illusion to users of a ver ...
.
The Burroughs B5000 instruction set includes the set of valid operations for the B5000, B5500 and B5700. It is not compatible with the B6500, B7500, B8500 or their successors.
Instruction streams on a B5000 contain 12-bit
syllables
A syllable is a basic unit of organization within a sequence of speech sounds, such as within a word, typically defined by linguists as a ''nucleus'' (most often a vowel) with optional sounds before or after that nucleus (''margins'', which are ...
, four to a word. The architecture has two modes, Word Mode
[ and Character Mode,][ and each has a separate repertoire of syllables. A processor may be either Control State or Normal State, and certain syllables are only permissible in Control State. The architecture does not provide for addressing registers or storage directly; all references are through the 1024 word Program Reference Table (PRT), current code segment, marked locations within the stack or to the A and B registers holding the top two locations on the stack. Burroughs numbers bits in a syllable from 0 (high bit) to 11 (low bit) and in a word from 0 (high bit) to 47 (low bit).
]
Word Mode
In Word Mode, there are four types of syllables.
The interpretation of the 10-bit relative address in Operand Call and Descriptor Call depends on the setting of several processor flags. For main programs (SALF off) it is always an offset into the Program Reference Table (PRT).
Character Mode
References
{{Comp-hardware-stub
Computer hardware
Stack machines
Virtual memory