Register–memory architecture

In computer engineering, a register–memory architecture is an instruction set architecture that allows operations to be performed on (or from) memory, as well as registers.^[1] If the architecture allows all operands to be in memory or in registers, or in combinations, it is called a "register plus memory" architecture.^[1]

In a register–memory approach one of the operands for operations such as the ADD operation may be in memory, while the other is in a register. This differs from a load–store architecture (used by RISC designs such as MIPS) in which both operands for an ADD operation must be in registers before the ADD.^[1]

An example of register-memory architecture is Intel x86.^[1] Examples of register plus memory architecture are:

• IBM System/360 and its successors, which support memory-to-memory fixed-point decimal arithmetic operations, but not binary integer or floating-point arithmetic operations;^[2][3][4]
• PDP-11, which supports memory or register source and destination operands for most two-operand integer operations;^[5]
• VAX, which supports memory or register source and destination operands for binary integer and floating-point arithmetic;^[6]
• Motorola 68000 series, which supports integer arithmetic with a memory source or destination, but not with a memory source and destination. However, the 68000 can move data memory-to-memory with nearly all addressing modes.^[7]

See also

• Load–store architecture
• Addressing mode