Re: TI-H: 832MB
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Re: TI-H: 832MB
>Question what is LBA and CHS??
Hard drives are organized as sectors of 512 bytes each. Obviously
today's hard drives have thousands of sectors. The HD controller
needs a way to identify individual sectors, and there are two methods:
logical block addressing (LBA) and the old methid, CHS (cylinders,
heads, sectors). Only drives made after like 1988 (complete guess)
allow LBA, which is the preferred method, but even LBA has limitations
that the latest hard drives are breaking.
LBA is pretty simple, it's basically just a 24 bit number that you
feed to the hard drive and this tells you which sector you want to
access. This has limits though:
2^24 sectors * 512 bytes/sector = 8 gigabyte max addressing
capability.
Since many drives are now larger than 8 gigs, they can no longer use
the standard ATA-3 LBA method directly. In fact, i'm not quite sure
the exact method they use, newer BIOS's probably just go back to CHS
on larger drives.
Instead of a single 24 bit number like in LBA, CHS uses three numbers:
sector (8 bit #), head (4 bit #), and cylinder (16 bit #). This gives
a maximum capacity of:
2^8*2^4*2^16 sectors * 512 bytes/sector = 128 gigs.
As you can see, LBA is more efficient on the controller end, but
because of its max capacity you need to revert back to CHS on drives
larger than 8 gigs. Once drives start hitting 128 gigs, LBA will
probably be extended to 32 or more bits within the ATA standard, as 32
bit LBA will give a max capacity of 2048 gigs.
-Mel
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