Editing Burroughs Large Systems (section)

==Instruction sets==

There are three distinct instruction sets for the Burroughs large systems. All three are based on short [[syllables]] that fit evenly into words.

===B5000, B5500 and B5700===

{{Main|B5000 instruction set}}

Programs on a B5000, B5500 and B5700 are made up of [[Syllable (computing)|12-bit syllables]], 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, 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)

===B6500 and successors===
{{Main|Burroughs B6x00-7x00 instruction set}}
Programs are made up of [[8-bit syllable]]s, which may be Name Call, Value Call, or form an operator, which may be from one to twelve syllables in length. There are less than 200 [[Operator (computer programming)|operators]], all of which fit into 8-bit syllables. Many of these operators are [[Polymorphism (computer science)|polymorphic]] depending on the kind of data being acted on as given by the tag. If we ignore the powerful string scanning, transfer, and edit operators, the basic set is only about 120 operators. If we remove the operators reserved for the operating system such as MVST and HALT, the set of operators commonly used by user-level programs is less than 100. The Name Call and Value Call syllables contain [[#AddressCouple|address couple]]s; the Operator syllables either use no addresses or use control words and descriptors on the stack.