Questions tagged [x86]

The Intel x86 family of architectures in general. Contemporary systems are OFF-TOPIC! Use the specific architecture’s tag if applicable.

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6
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1answer
337 views

How does an 8086 CPU remember the memory address where it should write back the operation’s result? [closed]

I have an instruction: ADD [BX][SI] + 5FFDH, EABFH and I want to know how it operates exactly on 8086 microprocessors. I've realized that this instruction ADD [BX][SI] + 5FFDH, EABFH, works in this ...
15
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4answers
2k views

Undocumented instructions in x86 CPU prior to 80386?

I have questions regarding some x86 instructions that were documented for the 80386 and later x86 CPUs, but not for earlier chips. "OR reg/mem16, immed8" (0x83/1) "AND reg/mem16, ...
11
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1answer
1k views

32-bit PCI riser cards: different types?

[copied from superuser.com] I'm duplicating an existing compact PC; I'd love to replace it with modern components, but for various reasons I can't. I'm having a tough time finding the correct 32-bit ...
10
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3answers
840 views

The NexGen's x86 internal RISC architecture

NexGen was best known for the unique implementation of the x86 architecture in its processors. NexGen's CPUs were designed very differently from other processors based on the x86 instruction set at ...
1
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1answer
328 views

What to do with stone age x86 computers? [closed]

Not sure if retro is proper place... I have two old notebooks with x86 processors in the 100s range of MHz. While nostalgics might appreciate them, I'm wondering if there is any proper point in ...
12
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1answer
813 views

Difference between INT 0x20 and INT 0x21 (0x4C)?

Checking the MS-DOS interrupt list we see INT 0x20 "Terminate the program" (see https://en.wikipedia.org/wiki/DOS_API) but if we check the same page we see INT 0x21 with function 0x4C will &...
10
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1answer
337 views

Did the Harris 80C286 differ from Intel's 80286 in its behaviour?

The Harris company, well known for being an early second source making x86 chips under license, eventually produced a fully static CMOS 80C286 of their own design (later known as the Intersil 80C286 ...
-5
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1answer
303 views

Is the Raspberry Pi Model B (2014) technically inferior to an original Xbox (2001) in compute power/specifically for emulators? [closed]

(I first asked this in the Raspberry Pi section, but it received no responses. I think this, Retrocomputing, might be a better fit.) I the year 2003, I had my Xbox chipped in order to be able to run ...
4
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2answers
222 views

Detecting the number of disk drives installed

When the BIOS gives control to the MBR (or the bootloader, for non-partitioned media), it passes the drive number from which the bootloader was loaded in the DL register. This number is most of the ...
18
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1answer
1k views

Detecting the external x87 FPU

On modern processors the x87 FPU is integrated in the CPU chip, but it used to be a separate chip before the 80486. So is there any way to detect its presence, and maybe even its generation (8087, ...
31
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4answers
9k views

Intel CPU bug in the '90s

My teacher who teaches "Logic" at the university told us a story about Intel processors, which goes: In the '90s Intel had a bug in the calculation of mathematical functions like sin/cos ...
12
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2answers
1k views

BIOS interrupts vs Hardware interrupts

On an x86 chip running in Real Mode, interrupts are resolved with the help of the IVT (Interrupt Vector Table), which is an array located at address 0000h:0000h that consists of 256 entries, 32-bit ...
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2answers
489 views

Should I install Gentoo i586 packages on my PC? [closed]

I've recently commenced revitalizing an HP Pavilion Slim. She's running an Intel Pentium, x86_64. I thought I'd give Gentoo a go because I've found it very appealing and as a Bedrock user I wanted to ...
11
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3answers
2k views

Swapping endian-ness on the 68000

In the 80s, the two great 16/32-bit desktop CPU architectures were the x86, used in the IBM PC and compatibles, and the 68000, used in the Amiga, Atari ST, Macintosh, early UNIX workstations and ...
6
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1answer
282 views

Which x87 first acquired the ability to flush denormal to zero?

On modern Intel FPUs, you can set a flag to cause all denormals to be automatically flushed to zero. On some workloads, this improves performance. I cannot find any mention of that flag in the data ...
5
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1answer
278 views

Do all Intel Celeron processors support “FCOMIP”? [closed]

I am interested, did all Celeron processors support the FCOMIP instruction? I've made a compiler for my programming language and it uses FCOMIP for every floating-point comparison. I've noticed that ...
18
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1answer
2k views

Identifying late 1990s embedded 486 UNIX-like system

I'm trying to identify the operating system on a Thermo-CRS C500 robot arm controller. From the specifications I know it runs on a 100 MHz 486 processor, and has 4 MB RAM and 2MB of flash/NVRAM ...
3
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2answers
466 views

What’s the last x86 CPU that didn’t place a limit on the size of a single instruction?

Although useless, it’s widely known the first Intel and derivative CPUs like the Z80 didn’t set a limit on the instruction size. This means that it was possible to fill the whole RAM/ROM with a single ...
6
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2answers
941 views

Are .COM executable binaries real mode or protected mode?

Windows and DOS binary executable files with the .EXE extension have an MZ header in them and nowadays also a PE header. But before these there used to also be .COM binary executable files and they ...
8
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2answers
2k views

First x86 Software Development Manual

These manuals are now called “Intel® 64 and IA-32 Architectures Software Developer Manuals”, and the current version is 71. What was the original name of this manual and when was it released?
14
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1answer
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What manages Upper Memory Blocks (UMBs) in MS-DOS?

I had always assumed that EMM386.EXE was responsible for managing the Upper Memory Blocks - UMBs - the memory space between 640KiB and 1MiB in real mode x86. For example, on MS-DOS 6.22, help emm386....
7
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5answers
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How does the ‘real mode flat model’ work?

I am interested in old Intel processors. I'll try to be as concise as possible. I have been studying both Jeff Duntemann's Assembly Language Step-by-Step - Chapter 4 and Modes of Memory Addressing on ...
16
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5answers
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What was the first multiprocessor x86 motherboard?

I know dual socket motherboards were around in the 90's before Intel released the Core series. And SMP hardware and operating systems have been around earlier than the PC platform of course. ...
0
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2answers
669 views

What 486 motherboard is this, with American Megatrends BIOS identifying is DPAQ-6156-043090-KF?

I've got an early 486 motherboard that doesn't seem to have a manufacturer name or FCC number on it and I'm having trouble identifying it. I've placed some photos of the motherboard in this Imgur ...
11
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1answer
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3 beeps on a 486 computer with an American Megatrends bios?

So far I've figured out that means something about the ram bit I haven't been able to figure out what the problem is Edit: video link
8
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2answers
672 views

What was the first x86 CPU to use a cache of any kind?

I believe the 80286 had a prefetch instruction queue, but did it have any other forms of cache? Was the 80386 the first x86 CPU to have a cache?
4
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1answer
706 views

What was the first Intel x86 processor with “Base + Index * Scale + Displacement” addressing mode?

As the title says, what's the first x86 processor from Intel that supports the following addressing mode? mov %reg, 8(base, index, 4) ^^^^^^^^^^^^^^^^^ where the content of %reg will be ...
26
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6answers
6k views

Why weren't discrete x86 CPUs ever used in game hardware?

Please don't point out APUs with x86_64 cores used in current generation game consoles, these are not part of the question I cannot recall a single arcade system or game console that ever used x86 ...
20
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7answers
17k views

What does the “x” in “x86” represent?

I have read the following in the x86 Wikipedia page: The term "x86" came into being because the names of several successors to Intel's 8086 processor end in "86", including the 80186, 80286, 80386 ...
22
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2answers
6k views

What was the last x86 CPU that did not have the x87 floating-point unit built in?

This Wikipedia page says the following: Most x86 processors since the Intel 80486 have had these x87 instructions implemented in the main CPU So the above quote implies that some CPUs that were ...
33
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2answers
5k views

Can an x86 CPU running in real mode be considered to be basically an 8086 CPU?

When an x86 CPU is running in real mode, can it be considered to be basically an 8086 CPU (or maybe 8088)? Or are there differences between the two?
8
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1answer
587 views

What's the fastest way to ignore keypresses?

I'm writing a game for the IBM PC (running MS-DOS), complete with fancy cutscenes. Unfortunately, though, the keys pressed during those fancy cutscenes are carried out once the fancy cutscene has ...
18
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2answers
2k views

Examples of operating systems using hardware task switching of x86 CPUs

Intel IA-32 architecture a.k.a. x86 offers hardware task switching capabilities since 80386. It includes TR (task register), memory segmentation features such as Task State Segment, task gates, call ...
1
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2answers
953 views

Does anyone have an x86 EGA draw pixel routine?

So far, I have gotten by with using the BIOS draw-pixel routine here: http://stanislavs.org/helppc/int_10-c.html This works of course, but I can't imagine that commercial games used this BIOS call as ...
14
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2answers
1k views

How to use the “darker” CGA palette using x86 Assembly?

For those of you retro developers out there, I am having a hard time figuring out how exactly to select the "darker" color palette in 320x200 CGA mode. Here's what I have so far: setup_cga_graphics: ...
5
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1answer
370 views

What was the first publication documenting AT&T syntax assembly language?

What was the first publication to document what is (now) known as AT&T syntax assembly language?
14
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1answer
538 views

SYSENTER/SYSEXIT broken on Pentium Pro and Pentium II?

I was just reading What is linux-gate.so.1?, and it says this: Intel recognized this problem early on and introduced a more efficient system call interface in the form of sysenter and sysexit ...
7
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4answers
1k views

Reason behind “ASCII Adjust” instructions being ASCII and not BCD?

I'm just curious if there was ever other instructions that were more ASCII-centric than the CISC associated ones we're left with now? Specifically, all the Binary Coded Decimal (BCD) instructions ...
7
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1answer
2k views

How do you put a 286 in Protected Mode?

From the Art of Intel x86 Assembly, Page 149, The 80386 added four control registers: CR0-CR3. These registers extend the msw registers of the 80286 [...] The book says earlier that, The 80286 ...
17
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3answers
1k views

x86 as a Pascal Machine?

From this answer by gsg about the usage of certain x86 instructions: Note that the x86 was originally designed as a Pascal machine, which is why there are instructions to support nested functions (...
5
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2answers
304 views

Mysterious things happening to stack when running a debug session

When I run a debug session using FreeDOS and DEBUG.EXE, I get a session like the following. I've added a description of what I saw as annotation on the image. Each step, I've printed out the stack ...
24
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2answers
6k 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 ...
24
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6answers
11k views

Can x86 processors run 8-bit applications?

I was wondering if it is possible to run 8-bit applications within QEMU. I know that the x86 architecture can run 16-bit applications, but can it also run 8-bit applications?