Chapter 7
IDE Quick Reference Chart

About IDE Drive Types

Most newer IDE systems can automatically configure for a BIOS Drive Type. However, there are still many drives and BIOSes in use that do not support the IDE Identify Drive command (see "The IDE Interface" in Chapter Two for more information). If this is the case and you do not have a drive that fits the parameters of one of the defined drive types for your particular BIOS, then you will have to enter a user-definable drive type. This chapter contains a table that allows you to simply look up the capacity of your particular drive and enter the corresponding parameters into the BIOS User Definable Drive Type.

The User Definable Drive Type does not have to use the physical parameters of a particular drive or even match the drive's capacity exactly. This is because most IDE drives do a translation so that they may be used in systems that do not support the drive type needed.

There are two types of specifications that you will encounter with this kind of hard drive. The first type of specifications are the physical (actual) specifications. These are the hard drive's real values. If you opened up the hard drive, looked inside and saw four heads, you would be looking at the physical (actual) number of heads. These physical specifications are supplied in Chapter 6 and indicated by PHDS, PCYL, and PSPT in the tables there. In some cases, the physical specifications are not available to us; we then supply you with the logical values.

The second type of specifications are the logical (translation) specifications. These are the heads, cylinders, and sectors that both the AT BIOS table and DOS can agree on. Most AT BIOSes have a limit of 16 heads and 1,024 cylinders. And DOS can never use more than 1,024 cylinders (unless special software is used). Most IDE hard drives exceed these limits. The IDE hard drive will do a mathematical conversion from the logical (translation) specifications to the physical (actual) specifications. These specifications are normally supplied by the hard drive manufacturer. The manufacturer may supply you with one set of logical (translation) specifications but by no means are you limited to those. Just remember to choose a drive type that is equal to or less than, but never more than the size of the drive in megabytes. The IDE drive will handle the translation from there.

If you have the physical (actual) specifications and a user-definable drive type in your BIOS, you may enter these in (but don't go over the DOS 1,024 cylinder limit). IDE Quick Reference Chart

On the table that follows, look up your drive capacity in column one and enter the specifications into the host system's user-definable drive type section.

This table is only valid when used with IDE-type hard drives.

The parameters provided are calculated not to exceed the formatted capacity specified. For example:

The parameter's list for 130MBs, 15HDs × 995CYL × 17SPT × 512BPS = 129,907,200 bytes.

If you know the exact capacity of the drive, you may increase the cylinder count to achieve maximum capacity. For example:

If the drive's capacity is 130.76MB, you could increase the cylinder count to 1001 for a capacity of 130,690,560 bytes, thus only forfeiting about 7KB.

You'll notice that the largest drive available with 17 sectors is 142MB. You can still use a drive with a higher capacity by increasing the sectors, such as the 143 to 528MB drives above.

In addition to this table, a list of manufacturers' recommended parameters is provided in Chapter 6 and indicated by LHDS, LCYL, and LSPT in the tables there.