Questions tagged [chs]

Cylinder-head-sector disk addressing: addressable range, direct use and conversion between physical, logical and LBA coordinates.

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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 ...
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7 votes
4 answers
424 views

Booting from SD card on a Compaq LTE 4/75 – DOS 6 works, Windows 95 doesn't

I'm in the process of restoring an old Compaq LTE Elite 4/75 laptop, which was missing its hard drive, so I thought I'd try booting using an SD-to-IDE adapter. On my main workstation I created an ...
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8 votes
1 answer
410 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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7 votes
3 answers
664 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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11 votes
3 answers
1k views

Default (as opposed to physical) read/write heads - what are they?

The Seagate U Series hard disk Product manual states that the drive has 16 "Default read/write heads" while it has 4/3/2/1 "Physical read/write heads" (depending on actual model). ...
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  • 515
10 votes
2 answers
436 views

How can the number of cylinders be different from the number of tracks?

In the IBM PC 5150 documentation, it is stated that the floppy drive has 40 tracks, 8 sectors/track and 512 bytes/sectors, for a total of 163 840 bytes of data. It makes sense, 40×8×512 = 163 840 ...
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  • 203
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
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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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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17 votes
1 answer
722 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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7 votes
2 answers
775 views

Compaq Contura Aero 4/33C - moving data to CF/IDE disk - No operating system detected

I've got a Compaq Contura aero 4/33 laptop with original DOS system installed. As the HDD is old and dying, I've decided to copy the drive to a CF card on a CF/IDE adapter. After connecting the drive,...
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