Questions tagged [bios]

To be used when asking questions about the Basic Input/Output System found on many computers.

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What was the first motherboard with UEFI?

UEFI is a publicly available (and a bit controversial) specification that replaces the legacy BIOS which has been in x86 computers since the original IBM PC (12 August 1981) At first, I know that this ...
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2 votes
4 answers
448 views

How can I make an 80 GB hard drive work with an Asus P2L97 motherboard?

I have a 80 GB PATA HDD (2003 Western Digital Caviar WD800 LBA) which is not recognized by my very old computer (Pentium 2 / Asus P2L97 motherboard). I thought it was due to the partitioning of the ...
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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 ...
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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This is purely academic, out of date, out of curiosity.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,...
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  • 223
14 votes
4 answers
4k views

Why have MS-DOS device drivers if the ROM BIOS provides access to the same devices already?

IO.SYS is an essential part of MS-DOS that contains the default MS-DOS device drivers. IBMBIO.COM is a system file in PC-DOS. It contains the built-in device drivers. Based on the answers of the ...
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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 ...
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13 votes
1 answer
604 views

Is there a way to trick my 386SX laptop into thinking there's a floppy drive installed?

I have a 1991 vintage AST Premium Exec 386SX/20 laptop, which is in excellent condition apart from that the original hard drive and the floppy drive are both dead. I've replaced the hard drive with a ...
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17 votes
3 answers
3k 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 ...
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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 ...
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12 votes
1 answer
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How can I enter BIOS setup on a Commodore PC 30-III?

I have a Commodore PC 30-III but I can't find a way to start the BIOS menu. It displays the following message during startup:
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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 ...
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8 votes
1 answer
421 views

Why is QEMU cutting off the last cylinder of the disk image?

I made a new disk image with the command dd if=/dev/zero of=hd.img bs=512 count=$(expr 16 \* 63 \* \( 15 \* 16 + 8 \)) which corresponds to creating a disk that would fill exactly with QEMU's default ...
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-1 votes
3 answers
351 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 ...
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8 votes
2 answers
771 views

DOSBox problem reading floppy boot sector using INT 0x13 on a drive mounted using MOUNT

I'm writing 16-bit boot sector code. It reads "sector 0" under VMware with all the fields, including the 0xaa55 sig, as expected but the same code copied to DOSBox under Win 8.1 (x64) reads ...
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3 votes
1 answer
301 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 ...
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7 votes
3 answers
677 views

How can I tell if my old PC supports > 137 GB hard drives?

I have an old PC from 1999 that has an ASUS P5A motherboard. When I power it on, it says ASUS P5A ACPI BIOS Revision 1011 Beta 005 and 05/02/2002-ALADDIN5-<<P5A>>: I recently read that up ...
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2 votes
0 answers
185 views

304-Keyboard or System Unit Error -- Compaq Prolinea 4/25s

I've recently got this error: 304-Keyboard or System Unit Error when booting my Compaq Prolinea. I've tested the keyboard on another computer and it's fine. I don't have another PS/2 keyboard to ...
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4 votes
2 answers
262 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 ...
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15 votes
2 answers
1k views

Was there ever a Linux kernel driver for accessing disks via BIOS?

If there is some piece of PC compatible hardware where there are no (publicly) existing drivers for Linux, the only option is to access the disk with BIOS calls. I'm aware that this imposes ...
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17 votes
2 answers
5k views

Why is there only one PS/2 port on my computer?

I have an old computer from around 1995. It's from a computer brand that I've never heard of called Samanna Compu-Solutions. I am unsure of the model. The problem is, I only have one PS/2 port to work ...
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6 votes
1 answer
611 views

Was it ever possible to access the full EGA color space in 200-line modes?

It's long been an established fact that the EGA only had four memory planes, which limited the number of colors on the screen to (24) 16. The best compatible monitors at the time had six TTL color ...
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12 votes
2 answers
3k views

Are BIOS ROMs interchangeable among different vendor's PCs?

For PC/AT, 80386, and 80486 machines from the late-1980s through early 1990s (e.g. retro machines, not modern), can you expect to pull a BIOS ROM from one machine and have it work fine in a different ...
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22 votes
2 answers
2k views

Which is the minimum set of interrupts/functions I should implement in a replacement BIOS for a home made IBM PC class computer?

I'm at the early stages of implementing a home-made IBM PC class computer (maybe AT class, I don't know yet). The CPU will be an actual 8088 chip, but everything else (except memory) will be ...
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1 vote
1 answer
86 views

How to configure HDD controller for CF in CHIPS LeAPset 117 (R1.09) bios

I'd like to use Compact Flash with 2,5" IDE adapter in i386 laptop. The bios is CHIPS LeAPset 117 (R1.09) and it requires specific configuration for HDD in order to work. I have 4GB CF card, where I ...
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18 votes
2 answers
2k views

How does Windows 9x determine which disk drivers correspond to which BIOS disks/DOS drive letters?

Windows 9x can employ two kinds of disk drivers: native protected-mode drivers and compatibility-mode DOS drivers, and the former are used in preference to the latter whenever possible. When Windows ...
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13 votes
2 answers
2k views

Hard coded hard drive BIOS geometries

Most old BIOSes on PCs and compatibles provided means to enter hard drive geometries (cylinder/head/sector as well as more esoteric things like write precomp) when configuring the machine. Some (AMI ...
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  • 1,565
5 votes
1 answer
476 views

Can't boot FAT32 larger than 2GB, unlike FAT16

Why can my PC not boot FAT larger than 2GB (FAT32) in legacy mode, but FAT16 and NTFS work fine? It just gives me a non-system disk error, while booting the same (DOS boot disk) files under FAT16 ...
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73 votes
8 answers
20k views

Why did IBM make the PC BIOS source code public?

IBM released the IBM 5150 Technical Reference manual in August, 1981, and included in it the fully commented source code listing for the BIOS. I find this odd for two reasons: IBM must have realized ...
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19 votes
4 answers
2k views

Did the IBM PC use the 8088's NMI line?

As I understand it, the Intel 8088 CPU used in the original IBM PC had two interrupt lines: INTR and NMI. INTR was fed from the Intel 8259 Programmable Interrupt Controller, which handled the IRQs ...
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29 votes
9 answers
10k views

How did early x86 BIOS programmers manage to program full blown TUIs given very few bytes of ROM/EPROM?

I've always wondered how so much functionality and relative luxuries(CMOS Configuration Utilities. See: https://geekprank.com/bios/ for an example) included with most popular x86 BIOSes could be ...
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8 votes
1 answer
669 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 ...
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  • 17k
0 votes
2 answers
758 views

Why can't BIOS be accessed in 64bit mode on Intel/AMD chips? [closed]

I was interested in a possible rewrite of dos to dos 64bit. In my research I found several references that state all current motherboard BIOS interrupts are not accessible from 64bit Long or 64bit ...
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5 votes
1 answer
9k views

Accessing a USB drive from DOS

I am setting up a new development computer with FreeDOS and can boot off the SATA or USB drive. This is my first new computer with sophisticated UEFI (I have CSM enabled). If I boot from the USB I ...
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7 votes
2 answers
3k views

Can DOS 6.22 recognize more than 504MB when the BIOS only supports CHS?

My CMOS setup correctly recognizes the geometry of the drive, (but does not support LBA). And FDISK in DOS 6.22 only recognizes 504MB. FDISK even shows the size of the primary partition as roughly ...
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2 votes
2 answers
1k 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 ...
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5 votes
2 answers
785 views

Starting a multi core CPU as single core [closed]

Is it possible to use a system with a modern, multi-core CPU with older operating systems that only support single core operation? Is this something that needs to be set in the BIOS? Does it depend ...
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11 votes
1 answer
1k views

How can I edit CMOS hard drive geometry settings on a 1991 PC?

First, I am NOT asking how to use the BIOS Setup utility. I'm asking how to OVERRIDE the built-in settings my BIOS Setup supports for the HD geometry. I have a 1991 NCR PC with a 386SX, on-board IDE, ...
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2 votes
1 answer
301 views

Support for 5.25-inch floppy drives on IBM Thinkcentre 8187 KUR

I have an IBM ThinkCentre 8187KUR desktop system. It has a bay for 5.25-inch floppies but no support in the BIOS. My question is, can I put in a PCI card to support floppy drive access and run the 5....
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14 votes
1 answer
4k views

What happens when PS1's "Fearful Harmony" is triggered?

When inserting an incompatible disc into a Playstation, after waiting awhile the screen will display very corrupt graphics and unsettling music will begin to play. This is unofficially referred to as "...
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4 votes
1 answer
867 views

XT-IDE Universal BIOS does not find master drive on XT CF Lite card

I have built a XT CF Lite v4.1 to boot my 286 with a compact flash card. I have configured it via DIP switches to address 300h and I am using the XT-IDE Universal BIOS 2.0.0 beta 3. This is I think ...
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  • 1,244
17 votes
1 answer
731 views

How did Drive Overlay programs break BIOS disk barriers on older PCs?

I was just reading a thread on Vogons about OnTrack and EZ-Drive setup, and it occurred to me that I have no idea how they work. Please explain why the barrier existed and then how the overlay ...
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10 votes
4 answers
2k views

How did DOS know where to load itself in upper memory?

If I remember correctly, you could ask DOS to load in upper memory by writing something like... DOS=UMB ...somewhere in the CONFIG.SYS file. But the question is, how did DOS know what portions of ...
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  • 329
12 votes
3 answers
2k views

Who were the first engineers to "cleanroom" the IBM PC BIOS?

In the first season of the AMC show Halt & Catch Fire, the protagonist "Cameron Howe" is introduced. Cameron portrays a rookie engineer who is recruited for being extraordinarily talented, and is ...
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11 votes
1 answer
719 views

Can the system's BIOS come from an ISA card?

If an ISA card was configured to respond to the address range of the system's BIOS (and the BIOS chips removed), could you boot from it in the same way as the system's default BIOS? Specifically, I'm ...
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  • 2,524
5 votes
2 answers
375 views

How to debug BIOS ROM incompatibility?

I'd like to use the XT-IDE Universal BIOS with an IBM XT 286 (5162), but it's known to be incompatible. With the card installed, it will not boot from a floppy from which it would otherwise boot (it ...
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  • 2,524
25 votes
12 answers
4k views

Why did CP/M and MS-DOS use the BIOS instead of their own drivers to access hardware?

Modern versions of Windows (and other modern operating systems I suppose) have their own drivers to access hardware. But as I have read, in the old days, if CP/M or MS-DOS wanted to access hardware, ...
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