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What does ISA stand for?
Instruction Set Architecture
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What is x86 short for?
Intel 80x86 ISA
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What are the "easy to remember" assembly names of the four general purpose 16-bit registers on the 8086 processor?
AX, BX, CX, DX
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What does AH refer to on the 8086 registers?
8 most significant bits of the AX register
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What does AL refer to on the 8086 registers?
8 least significant bits of the AX register
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Does the ISA make it possible to refer to the low or high bits of each 16-bit register individually?
- Yes
- - AH, AL
- - BH, BL
- - CH, CL
- - DH, DL
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True/False: Changing the value of AX will not change the values of AH and/or AL.
False, AH and AL are "tied" to the 16-bit register
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True/False: xH and xL registers can be used as 2-byte registers to store 2-byte quantities.
False, they are 8 bits, so they can store 1-byte.
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What are SI and DI?
- Two 16-bit index registers.
- - general purpose registers
- - by convention, they contain addresses (pointers)
- - CANNOT be decomposed into High and Low 1-byte registers
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Which 2-byte registers CANNOT be decomposed into HIGH and LOW 1-byte registers?
SI and DI
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What are the BP and SP registers?
- Two 16-bit special registers.
- - BP = Base pointer
- - SP = Stack pointer
*Storing in any of these registers will break you code
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What are the CS, DS, SS, ES registers?
- Four 16-bit segment registers
- - CS = Code Segment
- - DS = Data Segment
- - SS = Stack Segment
- - ES = Extra Segment
*Storing in any of these registers will break your code
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What is the IP register?
- 16-bit Instruction Pointer register.
- - point to the next instruction to execute
- - typically not used directly when writing assembly code
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What is the FLAGS register?
- - 16-bit register
- - contains "status bits" that has its individual name and meaning
- - collection of bits, not multi-bit value
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Name the six 16-bit registers that can be used as "variables"
AX, BX, CX, DX, SI, DI
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Name the 7 16-bit registers that cannot be used to store data. They are used to make your program run.
BP, SP, IP, CS, DS, SS, ES
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How many bits are addresses in the 8086 processor?
20, can reference 2d things
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What do addresses in the 8086 processor reference?
bytes
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CS point to the beginning of the:
code segment
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DS point to the beginning of the:
data segment
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SS points to the beginning of the:
stack segment
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How may bits are the EAX, EBX, ECX, EDX registers?
32-bit
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For backwards compatibility, AX, BX, CX, and DX refer to...
the 16 low bits of EAX, EBX, ECX, and EDX
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