All Questions
Tagged with instruction-set 8086
4
questions
52
votes
4
answers
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What did the 8086 (and 8088) do upon encountering an illegal instruction?
Preface: This question does in part intersect with Use of undocumented opcodes, but targets especially the 8086 instruction handling.
I was reading Tanenbaum's "Operating Systems, Design and ...
- 631
38
votes
1
answer
4k
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How did the 8086 interface with the 8087 FPU coprocessor?
The 8087 has many instructions - too many, it seems, to be encoded as part of the 8086 instruction set. How did the Intel 8086 interface with an Intel 8087 FPU that a user added?
Consider the ...
- 2,005
48
votes
4
answers
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Why are first four x86 General Purpose Registers named in such unintuitive order?
On x86 the first four general-purpose registers are named AX, CX, DX, BX. It would be quite intuitive if their indices (those used in instruction encoding) were in alphabetical order, but instead of ...
- 1,454
45
votes
8
answers
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Executable ASCII files before x86?
I've known about a technique allowing to bootstrap arbitrary 16-bit x86 code from a subset of instructions representable as printable ASCII bytes since the early 1990s.
The first example of an ASCII ...
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