Formatting:  a disk is the process of laying out on the surface of the disk, the areas that data can be written into. This forms a precise pattern. 

Each of the areas or parts of the disk have special names : 


  • Data is stored in blocks.
  • Data is read in blocks.
  • The unit of transfer between the disk drive and the CPU is in blocks.

Measuring Drive Performance: 

  • Average Access Time: For a storage device the average access time (or seek time ) is the amount of time the device takes to position its read/write heads over any spot in the medium. This measurement is an average because access times can vary greatly depending on the distance between the heads original location and their destination.
    For storage devices access times are measured in milliseconds (ms). For memory devices access times are measured in nanoseconds (ns).
    In a disk drive the access time depends on a combination of 2 factors- Revolutions per minute (rpm) & Time taken to move the heads from one track to another.
  • File Compression: One solution to the storage problem is to compress data. File compression or data compression is the technology for shrinking the size of a file, thereby freeing up space for more data and programs to reside on the disk.
    File compression is performed by software that uses mathematical algorithms to squeeze the data into smaller chunks by removing information that is not vital to the file or data. When the file is returned to its original size this data is reinserted so that the original data is reproduced exactly as it was before compression.
  • Data transfer rate: The speed at which a device can transfer data - how long it takes for one device to transfer data to another device. Speeds are expressed as a rate, or as some amount of data per unit time.
  • Drive Interface Standards: An important factor in determining how quickly a drive can read or write data is the type of controller that the drive uses. A disk controller connects the disk drive to the computers bus enabling the drive to exchange data with other devices.
    1. Enhanced integrated drive electronics (EIDE) is an enhanced version of IDE. It is a catch all term for drive interfaces based on this standard. Supports transfer rates of 33 MBps. The standard variants go by many different names including Fast IDE, ATA, Fast ATA and more.
    2. Small computer system interface (SCSI) was originally developed as a way to connect third party peripheral devices to mainframe computers. One way to think of SCSI is as an extension to the computers bus. As such all interface circuitry needed by the device has to be on the device itself. One benefit is to improve efficiency, allows higher transfer rates than EIDE.

File Security:  File security is necessary to prevent accidental or deliberate loss of data.  What kind of methods or precautions can be taken to protect data?

  • Keeping copies.
  • Physical Safeguards.
    • Lock the computer room
    • Lock away the discs
    • Use the write protect notches
  • Software Safeguards.
    • Use passwords
    • Issue ID and passwords

Basic Units of Measurement:  All information in the computer is handled using electrical components like the integrated circuits, semiconductors, all of which can recognize only two states – presence or absence of an electrical signal. Two symbols used to represent these two states are 0 and 1, and are known as BITS (an abbreviation for BInary DigiTS). 0 represents the absence of a signal, 1 represents the presence of a signal. A BIT is, therefore, the smallest unit of data in a computer and can either store a 0 or 1.. Bits are, therefore, combined together into larger units in order to hold greater range of values.

BYTES are typically a sequence of eight bits put together to create a single computer alphabetical or numerical character. More often referred to in larger multiples, bytes may appear as Kilobytes (1,024 bytes) ,  Megabytes (1,048,576 bytes),  GigaBytes (1,073,741,824),  TeraBytes (approx. 1,099,511,000,000 bytes),  or PetaBytes (approx. 1,125,899,900,000,000 bytes).

Bytes are used to quantify the amount of data digitally stored (on disks, tapes) or transmitted (over the internet), and are also used to measure the memory and document size.

Let's Review

  • 1 Nibble = 4 BITS = Half Byte
  • 1 Byte = 8 BITS = 2 Nibble
  • 1 Kilobyte = 1024 Bytes
  • 1 Megabyte = 1024 Kilobytes
  • 1 Gigabyte = 1024 Megabytes
  • 1 Terabyte = 1024 Gigabytes
  • and so on....

Multisession CD-R or CD-RW disc:  Multisession recording allows additional data to be written to a previously partially recorded CD-R or CD-RW disc.  Each session on the multisession disc has its own Lead-In Area,  Program Area and Lead-Out Area and may be connected to other sessions to function as a single volume (linked) or operate independently (multi-volume).  In addition to being written by a recorder the first session of a multisession disc can be,  alternatively,  prerecorded (stamped) at the factory. 

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