Let’s start by reviewing facts you’ve probably learned by working with Windows. Most operating systems, including Windows 95/98, manage hard drives by dividing their storage space into units known as partitions. So that you can access a partition, Windows associates a drive letter (such as C: or D:) with it. Before you can store data on a partition, you must format it. Formatting a partition organizes the associated space into what is called a filesystem, which provides space for storing the names and attributes of files as well as the data they contain. Windows supports several types of filesystem, such as FAT and FAT32; a newer filesystem type that provides more efficient storage, launches programs faster, and supports very large hard drives.

Partitions comprise the logical structure of a disk drive, the way humans and most computer programs understand the structure. However, disk drives have an underlying physical structure that more closely resembles the actual structure of the hardware. Figure 2-7 shows the logical and physical structure of a disk drive.

Figure 2-7. The structure of a hard disk

Mechanically, a hard disk is constructed of platters that resemble the phonograph records found in an old-fashioned jukebox. Each platter is associated with a read/write head that works much like the read/write head on a VCR, encoding data as a series of electromagnetic pulses. As the platter spins, the heads record data in concentric rings known as tracks, which are numbered beginning with zero. A hard disk may have hundreds or thousands of tracks.

All the tracks with the same radius are known as a cylinder. Like tracks, cylinders are numbered beginning with zero. The number of platters and cylinders of a drive determines the drive’s geometry. Some PCs require you to specify the drive geometry in the BIOS setup. Most modern PCs autodetect the drive geometry but let you specify a custom value if you prefer.

Most operating systems prefer to read or write only part of a track, rather than an entire track. Consequently, tracks are divided into a series of sectors, each of which holds a fixed number of bytes, usually 512.

To correctly access a sector, a program needs to know the geometry of the drive. Because it’s sometimes inconvenient to specify the geometry of a drive, some PC BIOS programs let you specify logical block addressing (LBA). LBA sequentially numbers sectors, letting programs read or write to a specified sector without the burden of specifying a cylinder or head number.

The first step in preparing your hard disk is viewing its partition information. Once you know how your hard disk is organized, you’ll be able to determine how to reorganize it to accommodate Linux. To view the partitions that exist on your hard disk drives, you can use the fdisk utility:

Red Hat Linux, as of the 7.2 release, no longer supports a partitionless installation,^[2] which was an option in previous versions that allowed you to install Linux without dedicating a partition for it. This is a good thing, because Linux doesn’t run particularly fast or reliably in a partitionless mode.

This means that you will have to devote at least three partitions to Linux during the installation process. By viewing the partitions on your hard drive, you can determine which of the following two cases best describes your system:

If you’re unsure whether your free space satisfies these criteria, simply begin the installation; the installation program will notify you if it is unable to proceed. In that case, you can return to this chapter to learn how to gain or add additional disk space.