Hardware Reference
In-Depth Information
As you can see, the ATA interface uses different-sized fields to store CHS values. Note
thattheATAlimitsarehigherthantheBIOSlimitsforcylindersandsectorsbutlowerthan
the BIOS limit for heads. The CHS limits for capacity according to the ATA-1 through
ATA-5 specification are as follows:
Max. Values
——————————————-
Cylinders 65,536
Heads 16
Sectors/Track 255
=============================
Total Sectors
267,386,880
——————————————-
Total Bytes 136,902,082,560
Megabytes (MB) 136,902
Mebibytes (MiB) 130,560
Gigabytes (GB) 136.9
Gibibytes (GiB) 127.5
When you combine the limitations of the BIOS and ATA CHS parameters, you end up
with the situation shown in
Table 7.19
.
Table 7.19 Combined BIOS and ATA CHS Parameter Limits
As you can see, the lowest common denominator of the combined CHS limits results in
maximum usable parameters of 1,024 cylinders, 16 heads, and 63 sectors, which results
in a maximum drive capacity of 528MB. This became known as the
528MB barrier
(also
called the
504MiB barrier
), and it affects virtually all PCs built in 1993 or earlier.
