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In contrast to the PDP-11's 3-bit fields, the VAX-11's 4-bit sub-bytes resulted in 16 addressing modes (0–15). However, addressing modes 0–3 were "short immediate" for immediate data of 6 bits or less (the 2 low-order bits of the addressing mode being the 2 high-order bits of the immediate data, when prepended to the remaining 4 bits in ...
The Intel 8085 ("eighty-eighty-five") is an 8-bit microprocessor produced by Intel and introduced in March 1976. [2] It is the last 8-bit microprocessor developed by Intel. It is software- binary compatible with the more-famous Intel 8080 with only two minor instructions added to support its added interrupt and serial input/output features.
An addressing mode specifies how to calculate the effective memory address of an operand by using information held in registers and/or constants contained within a machine instruction or elsewhere. In computer programming, addressing modes are primarily of interest to those who write in assembly languages and to compiler writers.
Architectures typically allow instructions to include some combination of operand addressing modes: Direct The instruction specifies a complete address Immediate The instruction specifies a value rather than an address Indexed The instruction specifies a register to use as an index. In some architecture the index is scaled by the operand length ...
first x86 processor with protected mode including segmentation based virtual memory management. Performance improved by a factor of 3 to 4 over 8086. Included instructions relating to protected mode. The 80286 had a 24-bit address bus.
The other advantage is that, because regular memory instructions are used to address devices, all of the CPU's addressing modes are available for the I/O as well as the memory, and instructions that perform an ALU operation directly on a memory operand (loading an operand from a memory location, storing the result to a memory location, or both ...
The "mod" field specifies the addressing mode for the register/memory ("r/m") operand. If the "mod" field is 11 2 , the "r/m" field encodes a register in the same manner as the "reg" field. However, if the "mod" field is anything else ( 00 2 , 01 2 , or 10 2 ), the "r/m" field specifies an addressing mode.
The 8086 [3] (also called iAPX 86) [4] is a 16-bit microprocessor chip designed by Intel between early 1976 [citation needed] and June 8, 1978, when it was released. [5] The Intel 8088, released July 1, 1979, [6] is a slightly modified chip with an external 8-bit data bus (allowing the use of cheaper and fewer supporting ICs), [note 1] and is notable as the processor used in the original IBM ...