How Hard Disks are organized Let's start by reviewing facts you've probably learned by working with Microsoft Windows. Most operating systems, including Microsoft Windows 95 and Windows 98, manage hard disk drives by dividing their storage space into units known as partitions. So that you can access a partition, Windows 95 and Windows 98 associate 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 file system, which provides space for storing the names and attributes of files as well as the data they contain. Microsoft Windows supports several types of file systems, such as FAT and FAT32, a newer filesystem type that provides more efficient storage, launches programs faster, and supports very large hard disk 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 2.3 shows the logical and physical structure of a disk drive. Figure 2.3: The structure of a hard disk Mechanically, a hard disk is constructed of platters that resemble the phonograph records found in a old-fashioned juke box. 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 determine the drive's geometry. Most PCs require you to specify the geometry of a drive in the BIOS setup. 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 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: 1. Click on the Start menu. The Start popup menu appears. 2. Select Programs. The Programs submenu appears. 3. From the Programs submenu, click on MS-DOS Prompt. An MS- DOS Prompt window appears. 4. Type fdisk and press Enter. The fdisk menu appears, as shown in Figure 2.4. The fdisk menu may not appear immediately. Instead, Windows may ask if you want to enable large disk support. If this occurs, type N and press Enter. You don't need to enable large disk support to view partition information. Figure 2.4: The fdisk Options screen 5. Type 5 and press Enter. This takes you to a screen, resembling the one shown in Figure 2.5, that lets you specify the current fixed disk drive. This screen displays partition information in a more readable format than the screen you obtain by using menu item 4, "Display Partition Information." The screen shows each hard disk drive and its size, numbering the drives beginning with 1. If a drive contains free space not allocated to a partition, the screen shows the amount of free space available. The screen also shows how much of the drive's space has been allocated to partitions, as a percentage of the total drive space. Under the information describing a drive, the screen shows the size of each partition that resides on the drive. The screen also shows the associated drive letter, if any.