IBM Personal Computers II. HardWare A. CPUs (Central Processing Devices) 1. Common Registers These registers, pointers, and flags are "lowest common denominator" 8088-8086 CPU oriented. Most programs available today on the PC market place, including DOS, make no attempt to use the special or enhanced instructions availible on the later CPUs which will execute xx88 code, such as the INTEL\80286, INTEL\80386DX, NEC V20, V30, V40, or V50. Recent trends are toward higher power applications which make use of, and sometimes require, extended registers GENERAL REGISTERS register definition AX accumulator (16 bit) AH accumulator high-order byte (8 bit) AL accumulator low order byte (8 bit) BX base (16 bit) BH base high-order byte (8 bit) BL base low-order byte (8 bit) CX count (16 bit) CH count high order byte (8 bit) CL count low order byte (8 bit) DX data (16 bit) DH date high order byte (8 bit) DL data low order byte (8 bit) I IBM Personal Computers D. CPUs (Central Processing Devices) 1. Common Registers SEGMENT REGISTERS register definition CS code segment (16 bit) DS data segment (16 bit) SS stack segment (16 bit) ES extra segment (16 bit) INDEX REGISTERS register definition DI destination index (16 bit) SI stack index (16 bit) SEGMENT REGISTERS register definition CS code segment (16 bit) DS data segment (16 bit) SS stack segment (16 bit) ES extra segment (16 bit) INDEX REGISTERS register definition DI destination index (16 bit) SI stack index (16 bit) I IBM Personal Computers D. CPUs (Central Processing Devices) 1. Common Registers POINTERS register definition SP stack pointer (16 bit) BP base pointer (16 bit) IP instruction pointer (16 bit) FLAGS AF, CF, DF, IF, OF, PF, SF, TF, ZF
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