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Maximum HD size for ATA133 controllers?

Posted on 2003-03-11
Medium Priority
Last Modified: 2010-04-03
What's the maximum hard drive ATA133 controllers can look at?

I presume it's something silly that current hard drives can't reach, but I wanted to know anyway.
Question by:Panimu
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Expert Comment

ID: 8110786
According to the official specs, Ultra-ATA/133 controllers can look at disks of 128 Petabytes. This is the maximum of disk space that can be adressed, thanks to 48 bit addressing.
LVL 18

Expert Comment

ID: 8110794
The cylinder address is a 16-bit value, broken down into two 8-bit segments. The least significant 8-bit segment is defined as the Cylinder Low register, and the most significant 8-bit segment is defined as the Cylinder High register. The head address is a 4-bit value, and is defined in the lower four bits of the Device/Head register. The sector address is an 8-bit value, and is defined in the Sector Number register. It is important to note that the first sector is defined as sector number 1 as no sector 0 (zero) exists.

Theoretically, we should be able to address up to 65,536 cylinders (216), address up to 16 heads (24) and address up to 255 sectors (28-1). Therefore, up to 267,386,880 sectors (65,536 x 16 x 255) can be addressed. At 512 bytes per sector, this yields a maximum theoretical capacity of about 136.9 GB.

With LBA addressing, the 28 available address bits (16 + 8 + 4) are viewed as a single LBA number. Since the value zero is included, up to 268,435,456 sectors (216 x 24 x 28) can be addressed for a maximum capacity of about 137.4 GB.

Your particular motherboard bios and controller may support something less, but most ATA133 would be capable of using the 120GB drives out there now.

The Operating System or hardware raid controllers can combine multiple drives into larger volumes, there are PCI raid controllers capable of striping 8 drives into one honkin' volume.

Expert Comment

ID: 8110909
Correct. Currently only 28 bit addressing is used, but the T13-committee (who are in charge of setting the standards of AT-equipment) are working on including the Ultra-ATA/133 specifications, which uses 48 bit addressing.

And 48 bit addressing leads to a theorethical maximum of approx. 128 PetaBytes

Author Comment

ID: 8112547
Maybe I was too vague in my question. I wanted to find out what -my- controller could look at. Its full specs are here

for the confusion points doubled.
LVL 18

Accepted Solution

chicagoan earned 160 total points
ID: 8112633
"Large LBA support" is 48 bit, so order yourself a 128 PetaByte drive from Wandalf, we're fresh out.

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