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[b] [c] Normally, an addressing mode without an index would simply use a bare ModR/M byte without a SIB byte at all, but this is necessary to encode an ESP-relative address ([ESP+disp0/8/32]). When MOD=00, a BASE of 101, which would specify EBP with zero displacement, instead specifies no base register and a 32-bit displacement.
The PC-relative addressing mode can be used to load a register with a value stored in program memory a short distance away from the current instruction. It can be seen as a special case of the "base plus offset" addressing mode, one that selects the program counter (PC) as the "base register".
In IBM System/360 through present day z/Architecture, an address constant or "adcon" is an assembly language data type which contains the address of a location in computer memory. An address constant can be one, two, three or four bytes long, although an adcon of less than four bytes is conventionally used to hold an expression for a small ...
For example, the top line is an 'H' record, the first 6 hex digits signify its relative starting location, and the last 6 hex digits represent the program's size. The lines throughout are similar, with each 'T' record consisting of 6 hex digits to signify that line's starting location, 2 hex digits to indicate the size (in bytes) of the line ...
Further improvements can be found by providing the address of both of the operands in a single instruction, for instance, ADD address 1, address 2. Such "two-address format" ISAs are very common. One can further extend the concept to a "three-address format" where the SAVE is also folded into an expanded ADD address 1, address 2, address of result.
The 80286 could address up to 16 MB of system memory in protected mode. However, the CPU was supposed to emulate an 8086's behavior in real mode, its startup mode, so that it could run operating systems and programs that were not written for protected mode. The 80286 did not force the A20 line to zero in real mode, however.
IO5 is a 5-bit I/O address covering the bit-addressable part of the I/O address space, i.e. the lower half (range: 0–31) IO6 is a 6-bit I/O address covering the full I/O address space (range: 0–63) D16 is a 16-bit data address covering 64 KiB; in parts with more than 64 KiB data space, the contents of the RAMPD segment register is prepended
Control units are assigned an address "capture" range. For example, a CU might be assigned range 20-2F or 40-7F. The purpose of this is to assist with the connection and prioritization of multiple control units to a channel. For example, a channel might have three disk control units at 20-2F, 50-5F, and 80-8F.