Cylinder 1024

At boot time the BIOS of many IBM PC compatibles can only access the first 1024 cylinder (hard disk)s of a hard disk as the BIOS, in Interrupt 13, uses Cylinder-head-sector addressing. CHS addressing only defines 10 bits for the cylinder count (2^10=1024).

This is a problem for operating systems on the x86 platform as the BIOS must be able to load the bootloader and the entire kernel (computer science) image into memory. Both of these must, therefore, be located on the first 1024 cylinders of the disk.

Older versions of Microsoft Windows resolved this by necessitating that the Operating System was installed to the first partition. Because of this bug, users of the Linux Operating System have traditionally created a /boot directory to reside within the first 1024 cylinders of the disk, containing little more than the kernel and bootloader.

= External links =

*[http://homepages.tesco.net./~J.deBoynePollard/FGA/os2-disc-and-volume-size-limits.html Disc and volume size limits ] includes a discussion of the cylinder 1024 limitation. *[http://www.tldp.org/HOWTO/Large-Disk-HOWTO-4.html Large Disk HOWTO - History of BIOS and IDE limits ]