Questions tagged [ibm-pc]

For questions about the early IBM PC, clones and compatible systems.

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22 votes
4 answers
3k views

Was it possible to cause persistent changes to a mid-1980s IBM-PC using POKE in GWBASIC?

TL;DR: Using the DEF SEG and POKE commands in GWBASIC, was there any way to make changes to an IBM-PC compatible computer that would (a) persist even after a reboot and (b) cause an increase in crash ...
  • 926
18 votes
3 answers
2k views

IBM PC Alt + numpad for entering character codes: firmware, BIOS or OS?

Back in the days of MS-DOS, when I needed to type a special character that wasn't part of the keyboard layout, I would press down the left Alt key and type out the character code on the numeric keypad ...
  • 1,208
23 votes
2 answers
4k views

How did Joysticks with more than 4 buttons and all those extra features work on a Game Port?

The question is pretty straight forward. How did they do so much more than the simple, unidirectional 4 axis of analog control, plus 4 on/off buttons? There was surprisingly precise force feedback ...
  • 331
12 votes
1 answer
3k views

What is this early 3D platformer?

Video: https://www.youtube.com/watch?v=8_-fcFivTS8&t=599s Image: I'm having a hard time tracking down a game I played when I was a kid. It was on DOS in the early 90s. It had flat-shaded polygon ...
  • 223
5 votes
5 answers
367 views

Chaining IRQs in x86 ROM code

Objective Summary: I need to write a sleep() function to be used in 8088 (PC/XT ISA) ROM code with 1 ms resolution. Though the question can be more generalized to chaining INTs with data in different ...
  • 1,197
38 votes
4 answers
7k views

Why does NumLock exist?

My keyboard has over a hundred keys on it. But there's one labelled NumLock. Pressing it turns the numeric keypad into a duplicate of the dedicated arrow keys just left of it. This doesn't seem useful ...
23 votes
2 answers
4k views

What is a "sympathetic bit"?

I am reading about BIOS in Phil Storrs PC Hardware book: What happens when we turn on a PC ? Next comes the incremental check of all the RAM memory. The RAM memory is written to, and read from, with ...
  • 541
22 votes
3 answers
3k views

How does the BIOS distinguish Interrupt(08h-12h) from INT instructions, vs. actual exceptions inside the CPU?

This is purely academic, out of date, out of curiosity. Let's go back to the 1990s, before Windows, when real-mode DOS programs were common. The BIOS assigned INT 08H+ for their own interrupt handlers,...
  • 323
4 votes
1 answer
170 views

IBM/Xebec XT Fixed Disk Adapter "Custom" Drive Types

It's generally believed that the IBM/Xebec Fixed Disk adapters were hardware limited to only four different drive geometries - of which, only the last revision of the card was user configurable (...
  • 1,197
9 votes
2 answers
1k views

How to determine BIOS-provided (INT 13h) hard disk geometry, and how to fix the MBR partition table to agree with it?

When transferring a hard drive from one computer to another, sometimes a situation can occur where the BIOS-provided CHS hard disk geometry (interrupt 13h without extensions) is different from the CHS ...
15 votes
2 answers
2k views

What information was "off limits" to IBM PC clone BIOS authors?

Back in the PC clone days the accepted legally defensible method of selling a non-IBM PC BIOS was using a "clean room" whereby an engineer who had never been exposed to proprietary IBM ...
  • 1,197
32 votes
7 answers
4k views

Did any PC software floating point use non-IEEE format?

During the 1980s, prior to the 486 (well, strictly speaking, prior to the discontinuing of the 486SX in the nineties), IBM PCs and compatibles had hardware floating point only in the form of an ...
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5 votes
1 answer
656 views

Who were the market for those "speed up your computer" shareware applications back in the day? [closed]

In the Swedish computer magazine PC Hemma ("Home PC") from February 1997 (p. 68), they included a floppy disk with shareware programs related to "trimming your PC", as well as a ...
  • 67
8 votes
1 answer
448 views

Meaning of KP_Begin and VK_CLEAR names of numpad 5

The key "5" at the standard keyboard numpad ("keypad" in XFree86) is named KP_Begin in XFree86 and VK_CLEAR in Windows virtual key space. What are these names originated in? Are ...
  • 440
15 votes
1 answer
883 views

Was there any software on the IBM PC that specifically took advantage of the NEC V20?

Back in the day I remember friends upgrading their IBM PCs (and compatibles) with a NEC V20 CPU. While this was mostly to get a bit more performance out of their machines over the stock Intel chip, I ...
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15 votes
9 answers
4k views

Cost of PC vs. Amiga 500 in Europe

Based on Commodore sales figures, and other historical claims, the Amiga achieved its peak popularity in 1990-91, with European sales being the leader. By 1990, with the rapid fall in PC clone prices, ...
  • 57.6k
0 votes
0 answers
168 views

What was the first PC-compatible computer to have a DRAM controller?

The original IBM PC used a timer from the 8254 PIT and a channel from the 8237 DMAC in order to refresh RAM with dummy reads (and I think used NMI to signal parity errors.) I'd like to know when PC's ...
  • 445
24 votes
1 answer
2k views

What is 'Adaptive Tile Refresh' in the context of Commander Keen?

The question Did John Carmack really invent "Adaptive Tile Refresh"? asks about the origins of the scrolling and drawing techniques used to allow an MS-DOS PC to provide a NES console-like ...
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31 votes
1 answer
7k views

Did John Carmack really invent "Adaptive Tile Refresh"?

John Carmack is credited with making fast-paced arcade games like Commander Keen possible on an IBM-PC that had no specialized graphics controllers suited for those, thanks to the "Adaptive Tile ...
1 vote
0 answers
319 views

What old LCD monitor am I thinking about?

I once had a PC with an LCD monitor and I'd like to remember what model that monitor was. Here's what I remember: It was basically a beige rectangular box with right angles on all corners. Only the ...
  • 293
17 votes
3 answers
4k views

In x86 real mode, how does BIOS know what hardware is present?

I know that BIOS is obsolete, hence why I'm asking here :-) BIOS needed to do things like start loading the OS, for which it (usually?) would have needed things like a hard disk driver. However, BIOS ...
13 votes
2 answers
2k views

If a PS/2 device on a 32-bit x86 sends a byte to the IO port 0x60 and you read it, what happens next?

I'm writing a hobby OS and the first thing I want to do is access PS/2 devices (it's a somewhat legacy, 32 bit OS, so I figured it's relevant to ask here?). I can see my PS/2 devices and I want to ...
30 votes
6 answers
7k views

Why did the monsters have "infinite invisible pillars" of hitboxes vertically in all versions of the DOOM engine?

Even in the last version of the DOOM engine, v1.9, used for Final DOOM, there is this strange limitation in which all the monsters have an invisible, infinitely tall "pillar" above and ...
  • 309
9 votes
2 answers
2k views

Why did the BIOS load the MBR at 0x7c00?

The IVT is at 0x0000-0x03ff while the BDA is at 0x0400-0x04ff but boot sectors are loaded at 0x7c00. What was at 0x0500-0x7bff that caused this convention? I'm also curious why some MBRs relocate ...
  • 445
21 votes
3 answers
6k views

Why doesn’t my VGA-to-HDMI converter work with my 286 PC?

I have a Commodore PC 30-III with a Cirrus ISA VGA card in it. I wanted to connect to an HDMI display by using a mini VGA-to-HDMI converter The converter doesn't generate any output. The machine ...
15 votes
4 answers
3k views

How was the real-time clock implemented in the original IBM PC and PC/XT?

I know that the IBM PC/AT added a battery backed real-time clock chip that independently maintained time whether the system was powered or not. I've also seen many of those big DS1287 clock chips on ...
  • 1,501
-1 votes
3 answers
355 views

Why did PCs for the longest time have a default "memory test" on boot which caused them to take a long time to start? [duplicate]

Not just "really back in the day", but even as late as "only a few years ago" (meaning 15-20 years), every time I started my PC, it would slowly "count through" the ...
  • 15
56 votes
6 answers
9k views

Why did some old MS-DOS games lack the ability to exit them?

While playing around in DOSBox-X, I'm reminded of some DOS games which appear to entirely lack the ability to exit/quit/close them. One prime example of that is "Paratrooper" from 1982. I've ...
  • 547
38 votes
4 answers
10k views

What caused older computer fans to be so much louder than they are today?

I had one of those bulky IBM 486 PCs in the mid-1990s. Desktop form factor. I think it was probably made somewhere in 1992. It made a lot of noises, pleasant ones to me, such as mechanical hard drive ...
17 votes
7 answers
6k views

Are there any good, non-abandoned PC emulators?

Mission: I'm trying to simulate a classic ~286/386/486/Pentium inside my modern PC (running Windows 10) in the most authentic way possible. Just a quick note to say that I (Sarah Walker) have decided ...
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10 votes
3 answers
3k views

What was that old FPS game where you shot rats in a sewer?

In the 1990s, I played an obscure shareware (I believe) FPS game for the PC (MS-DOS) which was closer in technology to Wolfenstein 3D than DOOM. It was rather dark, so I assume it had some sort of ...
  • 101
25 votes
1 answer
4k views

Did the original MS-DOS Quake not have a menu item for freelook, and if so, why?

I know that Quake (the 1996 MS-DOS game) is a "full" 3D engine, and always had some kind of mouse support. However, even the original Wolfenstein 3D from 1992 also had mouse support from the ...
  • 267
22 votes
2 answers
2k views

How does Laplink achieve "high speeds" on standard/legacy serial ports?

I have been using Laplink Pro 4.0a to transfer files between a modern Windows 10 desktop PC (via DOSBox) and several vintage DOS computers. Using a standard null-modem serial cable, in my testing it ...
  • 1,197
39 votes
11 answers
7k views

What's the origin of terminating strings by setting the high bit of the last character?

I was looking at a hex dump of the ROM BASIC from the original IBM PC and found some byte strings like this (ASCII dump is on the right): 50 52 49 4e d4 9d 4c 49 53 d4 9e 50 4f d3 1b 45 PRIN..LIS.....
  • 383
3 votes
1 answer
368 views

Award BIOS error code meaning

I have a faulty Asus SP-97V Pentium motherboard. It doesn't boot, but it definitely takes power and does something. I plugged a PCI diagnostics card into it, and it shows error codes C0 or C1. It ...
4 votes
1 answer
135 views

Quadram odd IBM PC card bracket

I came across an early IBM PC ISA realtime clock/calendar card made by Quadram called the "Chronograph" (picture). It's basically the same clock feature they incorporated into their ...
  • 1,197
14 votes
5 answers
2k views

Glue to attach rubber feet to a PC case?

I have an old PC case. I spray painted it because it was a little bit rusty. Now I'm trying to attach a set of rubber feet to it, but I have no idea what kind of glue to use. I tried hot glue, but it ...
5 votes
4 answers
2k views

9-pin vs 10-pin serial port ribbon cables

I'm (still) putting an old Pentium PC together. I just found that the connectors of my serial port's ribbon cable have one less hole than needed. The socket on the mainboard has 10 pins, but the 10th ...
2 votes
0 answers
79 views

Soltek SL-52B2 motherboard manual

I'm looking for the manual of this motherboard. Google can't seem to find one for this exact model, only similar ones. Help appreciated, thanks!
2 votes
1 answer
113 views

Asus SP97V motherboard not powering up

I found an Asus SP97V Pentium-I motherboard. It works with both AT and ATX power supplies. At least it's supposed to, because it actually doesn't. I put a Pentium 120 CPU, four RAM modules and a ...
7 votes
0 answers
346 views

What are the differences between MS-DOS and DR DOS FASTOPEN?

OS/2 Museum's history of DOS mentions the FASTOPEN.EXE TSR was introduced in DOS 3.3. Its entry on DOS 4.0 adds some implementation details. It reminded me of the DR DOS FASTOPEN=nnnnn directive in ...
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3 votes
0 answers
180 views

PC AT power supply not providing correct voltage

I'm refurbishing a Pentium 120 PC with an AT power supply. It seems to work, at least nothing pops or smokes, but there's a slight problem with voltages, particularly on the motherboard connectors. ...
5 votes
2 answers
405 views

Can I power a Windows 95-era AT PC with an ATX PSU, like this?

Is this the correct way to make the adapter? Will the "15A 120V AC ONLY" switch damage anything? The switch is illuminated. (glows when off)
13 votes
2 answers
645 views

What was special about "Vulcan" - the CP/M database program?

The Vulcan DBMS for CP/M micros was originally developed in 8080 assembly language by a contractor working for Jet Propulsion Lab, based on an earlier JPL mainframe program. This code went on to be ...
  • 57.6k
10 votes
2 answers
522 views

How do I terminate an ISA bus correctly?

I am stuck by designing a 8 Slot 16 Bit ISA Backplane Do I have to terminate an ISA bus? My search results are: No termination at all Some homebrew projects use active termination for all signals ...
  • 213
11 votes
2 answers
591 views

AdLib, YM3812 and Timers

For no particular reason I started reading up on the original AdLib Music Card, and it's clear that this card was little more than a stock Yamaha YM3812 music chip (aka OPL2) glued to a PC's 8-bit ISA ...
  • 1,197
13 votes
4 answers
3k views

CPU frequency / memory wait states at end of the 80s

According to the advertisements of the late eighties, you could find RAM having an access time ranging from 120 to 80 ns (150 to 210 cycle times). A 386SX-25 could execute a typical register to ...
  • 947
5 votes
2 answers
309 views

Config information on ancient 16-bit Multi I/O card

I need to build a retro machine so that I can access an HDD that required manual input of BIOS parameters. (Yes, I have that information.) The only ID I can find is ES1O/4A 280695 which yields nothing ...
14 votes
1 answer
888 views

What was the intended use for the character symbols for control codes in codepage 437?

Is there a well documented or well understood explanation for what was the intended purpose for the more haphazard glyph choices in the control code range of the original IBM PC character set? Maybe a ...
  • 2,205
10 votes
2 answers
844 views

When does an IBM-compatible PC keyboard controller dequeue scancodes?

There is a not-unheard-of technique in DOS software to detect certain keypresses (like Ctrl+Break) by intercepting the keyboard interrupt (IRQ 1) and reading the scancode directly from the keyboard ...
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