Sector Size on Virtual Machine

Background:

I noticed that on my virtual machines, the number of heads / cylinders on the disk are far larger than would technically be possible

A normal hard drive has 2 heads per platter, and up to 5 platters for a total of 10 heads.

This vm has 255!

root@ubuntu:~# fdisk -l

Disk /dev/sda: 21.5 GB, 21474836480 bytes

255 heads, 63 sectors/track, 2610 cylinders, total 41943040 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk identifier: 0x0002a643

Device Boot Start End Blocks Id System

/dev/sda1 * 2048 40105983 20051968 83 Linux

/dev/sda2 40108030 41940991 916481 5 Extended

/dev/sda5 40108032 41940991 916480 82 Linux swap / Solaris

Question:

41943040 sectors * 512 byte sectors = 21474836480 bytes (21GB)

41943040 sectors / 2610 cylinders = 16,070.130268199 sectors per cylinder (Strange that isn’t divisible evenly)

Apparently further research is needed.

  1. Why do virtual machines have 255 heads?
  2. Why do the number of sectors per cylinder no divide evenly?

If you have any ideas, leave them in the comments.

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About spuder
spuder is a "super computer" support engineer by day, and tinkerer / hobbyist by night.

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