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Questions tagged [8086]

For questions specifically regarding the Intel 8086 16-bit microprocessor

9
votes
4answers
2k views

Is there a cycle-exact 8086 emulator?

I'm trying to emulate programs from the 80s, but with an accurate clock-speed¹ (pretending its an 8086). Meaning that if a 8086 would take X ms/opcode, the emulator should take X ms (+- a bit of ...
4
votes
1answer
191 views

What instructions for the 8086 and subsequent x86 CPUs are not available in Long Mode?

I know from this answer that, Modern x86 CPUs are binary compatible with 8086. You can literally run 8086 binaries on a modern PC, in real mode. (The species analogy is a stretch here, but works ...
2
votes
1answer
2k views

“Quintword” is this a real word?

From the book Modern X86 Assembly Language Programming Quintword 80 Double extended-precision floating-point, packed BCD It goes on to say, Not surprisingly, most of the fundamental data ...
8
votes
8answers
3k views

Can one isolate processes on a 8086?

I've read that modern OSes rely on hardware-powered process isolation to prevent processes (and/or users) from clobbering each others' RAM. But on Intel processors, this hardware was first included in ...
30
votes
7answers
7k views

Why didn't the 8086 use linear addressing?

The 8086 used a segmented memory architecture where the linear address was computed from a 16-bit segment number and a 16-bit offset. This greatly complicated things from a programming perspective. ...
8
votes
2answers
345 views

8086 pinout and address space limit

It is tempting to say - and I have said - that Intel made a mistake in the design of the 8086 and 8088, in going from 16 bit addresses to only 20 bits; if they had even shifted the segment registers ...
14
votes
2answers
503 views

What are these tiny TSRs doing?

I've been puzzled by this for a while now. The (very old) game Phantasie comes with three small TSRs that are run prior to running the main game executable. This is the content of the file PH.BAT, ...
5
votes
3answers
470 views

How to do I/O with emulation code?

I have a partly-written emulation program for the 8086 CPU. And I'm not sure how to go about adding I/O capabilities to it. The emulator implements a subset of the 8086 instruction set described here. ...
14
votes
2answers
941 views

The start of x86: Intel 8080 vs Intel 8086?

Why is it said that all modern Intel processors of the x86 family are said to descent from the Intel 8086 and not the Intel 8080? From the Wikipedia article on the Intel 8086, The 8086 gave rise to ...
-1
votes
1answer
214 views

Run 8086 programs in dos using simple os other than any special software [closed]

I know to run 8086 using MASM & 8086 emulator, but how to run 8086 programs in dos without any special software.
28
votes
2answers
3k views

Why are first four x86 GPRs 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 ...
32
votes
5answers
4k views

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 ...
13
votes
3answers
718 views

Did the Intel 8086/8088 not guarantee the value of SS:SP immediately after RESET?

I'm poking at the Intel 8086/8088 (iAPX 86/88) User's Manual, which states on page 2-29 (PDF page 48), table 2-4, CPU State Following RESET, that the state of the CPU after the RESET pin rising ...
27
votes
4answers
4k views

What was the IBM PC cost saving for using the 8088 vs 8086?

The decision to use the 8088, a version of the 8086 with the data bus restricted to 8 bits, in the original IBM PC, seems strange on the face of it, certainly hurt performance and intuitively shouldn'...
75
votes
4answers
7k views

Were there 8086 coprocessors other than the 8087?

The 8087 math coprocessor for the 8086 (and descendants) nominally added floating point and transcendental (trigonometric and logarithmic) instructions to the 8086. Contrary to naive expectations, the ...
23
votes
4answers
3k views

What conventions and language extensions did people use to program the 8086 and 80286?

The 8086 is a 16 bit processor with a 20 bit segmented address space, famous for being used in the IBM PC. It is also infamous for being tricky to program for. I am currently writing what is ...