26
votes
Accepted
When was the CHS (cylinder - head - sector) system invented and what was before it?
It seems the question is mixing up physical disk access (CHS) with a logical access scheme used at a higher level. LBA is and always has been an issue at the OS level. The fact that some disk ...
- 236k
22
votes
Accepted
How did Drive Overlay programs break BIOS disk barriers on older PCs?
The reference for this is DEW Associates’ pages on the topic.
Multiple barriers have existed in the history of hard drives on PC compatibles. The main ones are the barriers at 528 MB (504 MiB) barrier,...
- 131k
20
votes
Does DOS require partitions to be aligned at a cylinder boundary?
The Large Disk HOWTO is correct. MS-DOS requires CHS EBRs (type ID 5) – but only CHS EBRs – to be cylinder-aligned.
This can be discovered by studying internal DOS data structures, especially the one ...
- 25.2k
19
votes
Accepted
Default (as opposed to physical) read/write heads - what are they?
The physical geometry how many heads the drive actually has is not the same as the logical geometry of how many heads is presented to the PC by the drive.
By translating the geometry, the drive can be ...
- 37.2k
16
votes
Accepted
How can the number of cylinders supported by a floppy drive be different from the number of tracks?
As far as I can tell, the first edition of the IBM 5150 Technical Reference is the only IBM manual which mentions 45 cylinders. Few Technical References document the FDC, which is where the “45 ...
- 131k
15
votes
When was the CHS (cylinder - head - sector) system invented and what was before it?
The cylinder number determines the position the read-write head write must move to, the head number determines which of the multiple read-write heads the disk drive should use, and the sector number ...
- 30.5k
15
votes
Accepted
Hard coded hard drive BIOS geometries
The tables were built using the parameters for various real hard drives. For example, type 1 is used for the original Shugart drives used in the PC XT (ST506). So the intention was for the drive types ...
- 131k
14
votes
Accepted
Can DOS 6.22 recognize more than 504MB when the BIOS only supports CHS?
It can be done using a third-party "disk manager", such as OnTrack Disk Manager and EZ-Drive. At the end of the DOS era, these came bundled with many hard disks.
https://en.wikipedia.org/wiki/...
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13
votes
Accepted
How can I edit CMOS hard drive geometry settings on a 1991 PC?
In all the BIOS setups I was dealing with that have similarly 47 drives to chose from the first or the last one was editable directly in BIOS SETUP for manual settings. Sometimes the manual settings ...
- 7,354
13
votes
Accepted
Why is QEMU cutting off the last cylinder of the disk image?
QEMU is not at fault here. The discrepancy comes from the BIOS.
When I create a disk image as described in the question, then attach it to a QEMU virtual machine and use the info qtree command in the ...
- 25.2k
13
votes
How to determine BIOS-provided (INT 13h) hard disk geometry, and how to fix the MBR partition table to agree with it?
If you can manage to boot the computer from a DOS floppy or some other device, you should be able to use the classic partitioning tool, Ranish Partition Manager. (I recommend version 2.40 or 2.44; ...
- 25.2k
12
votes
Can Linux boot beyond 1023 cylinders on old BIOS?
As the large disk howto explains, LILO bootstraps through a loader that still uses the BIOS, this is why LILO didn't work for you.
On the other hand, nuni does not use BIOS services but accesses IDE ...
- 30.5k
12
votes
Accepted
Booting from SD card on a Compaq LTE 4/75 – DOS 6 works, Windows 95 doesn't
The problem is in the geometry. Not in the physical disk geometry, but rather in the translation how the BIOS must translate the geometry for DOS when using disks larger than 1024 cylinders.
The ...
- 37.2k
11
votes
How can I tell if my old PC supports > 137 GB hard drives?
Very briefly:
The way harddisks are addressed changed over time. Originally, you'd specify cylinder/head/sector (CHS), then it switched to logical block addresses (LBA), and the commands for those ...
- 30.5k
11
votes
Accepted
Origin of CHS geometry limits in BIOS calls
The API dates back to the original IBM PC, and its floppy disk support. Quoting the 5150’s BIOS listing:
REGISTERS FOR READ/WRITE/VERIFY/FORMAT
(DL) - DRIVE NUMBER (0-3 ALLOWED, VALUE CHECKED)
(DH) - ...
- 131k
10
votes
Default (as opposed to physical) read/write heads - what are they?
Modern hard drives are not addressed by Cylinder, Head and Sector (CHS) coordinates, but by Linear Block Address (LBA). This is mostly due to the number of sectors per track changing across the width ...
- 16.9k
9
votes
How can the number of cylinders supported by a floppy drive be different from the number of tracks?
Floppy disk drives could usually mechanically access more than 40 tracks, but only 40 were actually used, "formatted".
First track is on the outer edge of the disk, there is a detector than ...
- 3,745
9
votes
How can I make an 80 GB hard drive work with an Asus P2L97 motherboard?
You need a BIOS update. Version 1009 from November 1999 already fixes it according to release notes. It is the final official BIOS version and newer beta releases exist, but must be chosen carefully ...
- 37.2k
9
votes
Can Linux boot beyond 1023 cylinders on old BIOS?
LILO only requires the /boot partition to be within the area accessible by the BIOS. AFAIK there is no technical reason to not have /boot, on a FAT partition, so you could have a symbolic link from /...
- 8,311
8
votes
Origin of CHS geometry limits in BIOS calls
Short version : The reason
why cylinder and sector are combined the way they are into single word in register CX is that the Xebec hard drive controller chipset used on XT hard drive controller card ...
- 37.2k
7
votes
How to determine BIOS-provided (INT 13h) hard disk geometry, and how to fix the MBR partition table to agree with it?
There are various different methods of converting the drive physical geometry to logical BIOS geometry.
It sounds like the drive was originally been used with "ECHS" or "Large" ...
- 37.2k
6
votes
When was the CHS (cylinder - head - sector) system invented and what was before it?
So the question is how the blocks of data were really addressed in old HDDs? Did they make use of CHS or some other system?
They used cylinder number. Maybe also head number (i.e., disk platter ...
- 6,504
6
votes
Booting from SD card on a Compaq LTE 4/75 – DOS 6 works, Windows 95 doesn't
Whew, I've got it solved!
I took one of the disk images with Windows 95 installed on it, and examined it with a hex editor. I noticed that when the Windows installer program initially sets up the ...
- 765
6
votes
How can I tell if my old PC supports > 137 GB hard drives?
That BIOS screen clearly says that it detects the drive as roughly 8 GB. The parameters say 16383/16/63 as so this BIOS cannot detect or provide the extended disk services that would allow the drive ...
- 37.2k
6
votes
Accepted
Did any PC disk defragmentor optimize cylinder position?
That's a matter for file system geometry, not defragmenters. Consider a disk as having blocks logically numbered 1 to N. Arranging those blocks on the disk is done by (depending on system) either ...
- 38.2k
6
votes
Did any PC disk defragmentor optimize cylinder position?
There was a single PC/DOS defragmentation software that paid attention to disk geometry: FastTrax. Its claim to fame was that it didn't merely defragment files, but also arranged them to cylinder/...
- 301
5
votes
Can Linux boot beyond 1023 cylinders on old BIOS?
We can make this work.
Have a floppy disk that can boot the linux on your hard disk, either using lilo or syslinux to load kernel from floppy disk. Make sure you have access to the boot command ...
- 1,888
5
votes
Did any PC disk defragmentor optimize cylinder position?
"each side of each disk had its own read head, and all of them could be doing I/O simultaneously" - no, they could not.
There was a single disk controller able to select one head at a time ...
- 37.2k
4
votes
Compaq Contura Aero 4/33C - moving data to CF/IDE disk - No operating system detected
Because these drives have different geometries and multiple partitions, you can't dd the whole thing in one pass and expect everything to work. In particular, your DOS partitition which was located ...
- 11.5k
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