Hardware Fundamentals
© Copyright Brian Brown, 1992-2000. All rights reserved.
This material may not be reproduced in printed or electronic format without the express permission of the author.

Disk Management
The objective of this section is to

• discuss methods for managing disks

At the end of this section, you should be able to

• handle disks properly
• format disks
• structure disk file organization using directories

Floppy Diskettes

Floppy disks are flexible removable storage media for computers. Floppy diskettes are made from plastic. A circular disk is enclosed inside a square protective case. The disk is coated with magnetic particles. The magnetic particles act as a storage medium for data. More information about floppy diskettes is found here

Diskettes are inserted into a floppy drive. The drive spins the diskettes at a speed of 360RPM, and use a read/write head that touches the surface of the diskette. They come in a range of sizes and storage capacities. The following table shows some common floppy disk sizes and storage capacities.

Floppy Diskette Management
Proper care and maintenance of diskettes used to store data will reduce the likelihood of destroyed or corrupted data. Whilst application software is easily reloaded, data is very difficult and expensive to reconstruct, thus is a very important commodity for any business organization.

Handling Precautions
The following is a summary of correct handling precautions for diskettes.

• Do not touch the exposed surface of the diskette
• Avoid placing the diskette near possible heat sources (on top of the monitor)
• Keep the diskette away from magnetic fields (power supplies, fans, magnets, monitor displays)
• Do not write on the diskette except for a soft felt pen
• Do not remove or insert the diskette into the drive if the drive light is on
• Don't bend the disk, or leave the diskette lying on the desktop area. Use a proper storage jacket (for 5¼" diskettes), or store the diskettes in a storage container.

Formatting Diskettes
MSDOS disks are formatted using the command format. This writes the appropriate directory structures and file allocation tables to the diskette, allowing the storage of files.

The actual process of formatting diskettes has been covered in previous modules (OS100, SF100). In Windows95 or WindowsNT, disks can be formatted in an MSDOS command prompt window by using the Format command, or by rightclicking the Floppy drive A icon in my computer and selecting the Format option from the popup menu.

Fig 3a: Format menu in Windows95

When this option is selected, the following dialog box appears, which allows the user to create a system diskette [which can be used to boot the computer system with Windows95], and a quick format, which only erases existing files and data which is stored on the diskette.

Fig 3b: Format dialog box in Windows95

Write Permit/Protect Notch
Diskettes are provided with a write protect notch. In 5¼" diskettes, the write protect notch is covered with a sticker. This prevents writing to the diskette.

In 3½" diskettes, the write protect tab is slid towards the front of the diskette. In the diagram below, the write protect tab is shown in the write enable position.

Fig 3c: Write Protect Notch on floppy diskette

Hard Disk Management
Hard disk drives are normally referred to as drive C:, drive D:. These drives are fixed (non-removable) and have a large storage capacity. Hard disks are generally supplied from the manufacturer as blank, though many new computers now have the operating system pre-installed on the hard disk drive.

The disks are low-level formatted first using a special program, which writes timing and other information to the disk, as well as performing a surface analysis. The disks are made of thin ceramic or metal, and coated with magnetic particles. The disks rotate at speeds of 3600RPM or higher. They are normally air sealed to prevent dust particles and other debris damaging the surface of the disk. More information about hard disk drives is found here.

Low Level Format
A low level format erases all information on the disk. One purpose of a low level format is to build a bad block table on the disk which holds any defective tracks and sectors. Another purpose of a low level format is to determine an interleave factor for writing sector information.

Partitioning Disks
Partitioning a disk is dividing the disk into areas, specifying which areas are to be used for MSDOS or some other operating system. After partitioning the disk, the partition is made active then formatted using the operating systems format utility. This may also include adding special boot files to the partition which allows the partition to boot the operating system from that partition on the hard disk.

The MSDOS fdisk utility allows the hard disk to be split up into a number of parts (called partitions). Each partition may be a different size, and can contain different operating systems (MSDOS on one partition, UNIX on another, OS/2 on another, etc). Only one partition may be the active partition. This is the partition which the machine will boot from. The active partition may be switched from one partition to another partition by running the fdisk program.

FDISK provides a menu interface for creating partitions, specifying their sizes, changing the active partition, and deleting partitions.

MSDOS Partition Types
MSDOS provides support for THREE different partition types.

• Primary MSDOS Partition
  The primary MSDOS partition is one that holds IO.SYS, MSDOS.SYS and COMMAND.COM. It is used to start MSDOS from the hard disk, and will appear as drive C:. The primary partition is always known as C:
  
  
• Extended MSDOS Partition
  The extended MSDOS partition is an area where non MSDOS system files are stored. It is optional. The extended partition supports up to 23 logical drives. When an extended partition is created, you divide it into one or more logical drives (E to Z). Logical drives are areas of the disk (in the extended partition) that MSDOS treats as separate disk drives. An extended partition must be assigned at least one logical drive. An MSDOS primary partition must exist before an extended partition can be created.
  
  
• Non MSDOS Partition
  These partition types are used to reserve disk space for other operating systems like OS/2, Novell Netware or UNIX. The MSDOS version of FDISK cannt create a non-MSDOS partition. You must use the partition utility provided with the particular operating system.
  
  

Partition Sizes
MSDOS v3.x supported partition sizes up to 32MB in size. MSDOS 5.0 supports partition sizes up to 2GB.

More than one Hard Disk in your system
The first hard disk which has the primary partition is used to load MSDOS. The second drive can only contain extended MSDOS partitions.

The MSDOS FDISK Utility
This utility is used to create, modify, display and delete partitions under MSDOS. When run, it displays the main option screen, which looks like,

Fig 3d: Fdisk program

If there is more than one hard drive fitted to the computer system, a fifth option will be displayed (change current drive).

Displaying partition information using FDISK
Selecting option 4 (Display partition information) displays the current partitions on the selected drive. If the drive has not been previously partitioned, there will be no defined partitions.

Fig 3e: Fdisk: Display partitions

The following screen shows a single drive system which has been previously partitioned with a single MSDOS primary partition (type=PRI DOS) of 2047MB. Note that the status of the partition has been made active (A).

Creating an MSDOS partition or logical MSDOS drive using FDISK
If there are no partitions defined, or there is free space on the disk, partitions can be created. Selecting option 1 (create partition) from the main menu of FDISK displays the following screen.

Fig 3f: Fdisk: Create partitions

To create a primary MSDOS partition choose option 1.

To create an extended MSDOS partition (only if a primary partition already exists), choose option 2.

To assign logical drive letters to parts of the extended partition (if it exists), choose option 3.

Each selection will ask how much disk space is to be allocated. This can be typed in as a number of megabytes (eg, 40 would allocate 40MB), or as a percentage (eg, 50% would use half the space).

Deleting and MSDOS partition or logical MSDOS drive using FDISK
If you delete a partition, all information present in the partition is lost. To delete a partition or logical drive, choose option 3 (delete partition) from the main FDISK menu. The following screen is displayed.

Fig 3g: Fdisk: Deleting partitions

Logical drives must be deleted in any extended partition before that extended partition can be deleted. Primary partitions can only be deleted if all extended partitions have been deleted first.

Deleting a Primary MSDOS partition using FDISK
The computer system will restart if any changes are made to the partition tables using FDISK. After using FDISK, you must format the partitions created to prepare them for use by MSDOS.

High Level Formatting
Before hard disks can be used by an operating system, they must be prepared for use. Once a partition has been created and made active, it is formatted using the FORMAT command.

	FORMAT C:/S/V

This makes the current active partition on the hard disk a BOOTABLE (/S) copy of DOS, and requests a volume name (/V). Once this is completed, the computer is re-booted WITHOUT a system diskette in drive A: and DOS is loaded from drive C:

High level formatting writes directory information and hidden tables onto the disk, which permits the later storage of files. These tables keep track of file locations, sizes, modification dates and other information. In MSDOS and Windows95, they are known as File Allocation Tables [FAT tables].

Summary
Data is expensive to recreate, so good handling and storage methods are essential.

Before diskettes can be used, they must be formatted for use. This is done using the Format command. It writes directory information onto the diskette which allows it to store files.

Hard disk drives must be partitioned before use. The active partition is that partition that the computers looks for the operating system files when it is started. In MSDOS and Windows, the primary partition is known as Drive C.

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© Copyright Brian Brown, 1992-2000. All rights reserved.