Computer Hardware

An additional approach to get around the problem of complex internal geometry is to change the way the drive is addressed completely. Instead of using the logical geometry numbers directly, most modern drives can be contacted using logical block addressing (LBA). With this method a totally different form of logical “geometry” is used: the sectors are just given a numerical string starting with 0. Again, the drive just internally translates these sequential numbers into physical sector locations. So the drive above would have sectors numbered from 0 to 7,539,839. This is just yet another way of providing access to the same sectors. Today’s drives are over 8.4 GB capacity barriers. The largest logical parameters that can be used for accessing a standard IDE/ATA drive are 1,024 cylinders, 256 heads, and 63 sectors. Since the ATA standard only allows a maximum of 16 for the number of heads, BIOS translation is used to trim down the number of heads and increase the number of cylinders in the specification. The practical result of all of this is that the largest logical geometry numbers for IDE/ATA drives are 16,383 cylinders, 16 starts and 63 sectors. This yields a maximum capacity of 8.4 GB.