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An Acronym for __L__ogical __B__lock __A__ddressing

[LBA] gives sectors a linear number starting with 0, as opposed to the classic cylinder-head-sector (CHS) addressing.

LBA addresses can be 28 bit or 48 bit wide. If your disk has 512 byte sectors (fairly common), a 28 bit LBA device can address 128 GB of disk. Here's the maths:

<verbatim>
512 byte sectors = 2^9 Bytes.
1 GB = 2 ^ 30 Bytes.

2 ^ 28  * 2 ^ 9 Bytes = 2 ^ 37 Bytes = 137438953472 Bytes
2 ^ 37 Bytes / 2 ^ 30 = 2 ^ 7 GB = 128 GB
</verbatim>

Disk manufacturers actually use GiB (10^9, as opposed to 1024^3):
<verbatim>
2 ^ 37 bytes = 137438953472 Bytes = 137.43 GiB
</verbatim>

This is the reason for older OS's or controllers failing to detect a large disk correctly.

48 bit LBA offers much larger disks:

<verbatim>
2 ^ 48 * 2 ^ 9 Bytes / 2 ^ 30 = 2 ^ 27 GB = 134217728 GB = 128 EB
</verbatim>

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Part of CategoryHardware

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Version 4, saved on Sunday, September 26, 2004 7:29:27 pm by DanielLawson

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