KarbosGuide.com. Module 4b1.

Hard disks - an introduction

The contents:

  • A technique from the 1950's.

    On the following pages:

  • The construction of a hard disk
  • Harddisk developments
  • The controller principles
  • The harddisk interface
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  • Hard disks consist of one or more magnetic disks contained in a box. They are used as storage media in the PC, where you store programs and other digital data.

    Forty years old technique

    The magnetic storage hard disk is based on a more than 40 year old technology. It has been and still is being improved rapidly. Hard disks continue to shrink in size, gain increased storage capacity and increased transfer speeds. The development has been tremendous during the last 10 years. Indications are that this will continue for a long time.


    First, let us look at the hard disk history. IBM introduced the first hard disk in 1957, when data usually was stored on tapes. The first 305 RAMAC (Random Access Method of Accounting and Control) consisted of 50 platters, 24 inch diameter, with a total capacity of 5 MB, a huge storage medium for its time. It cost $35,000 annually in leasing fees (IBM would not sell it outright) and was twice the size of a refrigerator. You see it to the right here:

    The RAMAC was used for calculating the results at the Olympic games in 1960. In 1962 the disks were made removable introducing the diskpack. In 1964 the CRC algorithm was in use giving a higher degree of data security on the disks.

    The first model to use "float on air" technology for the read/write heads was named Winchester 3030 of 1973. So named because it was developed in Winchester, England and had two sides, each of which could store 30 MB. To some people, this designation was reminiscent of the famous Winchester 3030 repeating rifle.

    Later, the disk platters shrunk to 14" and 8" diameter. They were installed in towers containing dozens of these magnetic platters.

    In the early years of PC development, the low cost floppy drives were the preferred storage media. But with IBM's XT in 1983-84, the hard disk became the preferred medium. The first hard disks were rather large units (5.25" diameter) and of poor quality. I have replaced numerous 5, 10 and 20 MB hard disks during 1986-88, since these early PC hard disks had an incredibly short life span. Since then they have improved a lot.

    The modern hard disks are 3.5" diameter. A typical example is the Quantum Fireball, which you see above. The cover plate has been removed, so you can see the top arm with its read/write head.

    Important things to look for

    Hard disks can be found in much smaller sizes (all the way down to match box size). However, for ordinary, stationary PCs the 3.5" is the best. They are inexpensive to manufacture, stable and they are fast.

    When buying a PC, It is a good rule to include a large and fast hard disk. You can never buy too large a hard disk and the data transfer speed is decisive for the PC's performance.

    An evaluation of the hard disk, its configuration and performance, involves several different technologies. That is the subject of this page:

    The mechanical disk

    The physical disk construction, RPM (Rotations Per Minute), the construction of the read/write head, the data density, etc.

    The cache

    The hard disk always has some cache RAM onboard. It serves as a buffer, for best utilization of the data being read.

    The interface

    The connection between the hard disk and other PC components. That is called interface - the connection to a data bus, the controller principle.

    Formatting etc.

    Disk formatting, control system, cache, etc.

    I want to illustrate the inter-action between these features, thus giving a comprehensive picture of the hard disk and its technologies.

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    Learn more

    Also see Module 4c about optical media (CDROM and DVD).

    Also read about EIDE and UDMA

    And about the most advanced and elegant controller principle of all: SCSI.

    Read module 7a about monitors, and 7b on graphics card.

    Read module 7c about sound cards, and 7d on digital sound and music.

    HD Tach - a fine program to test harddisks.

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