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					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.

				
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