Development of Computers

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Development of Computers The earliest known device to record computations was the abacus. It dates back to ancient times and was invented by the Chinese. Ten beads were strung onto wires attached to a frame. Addition and subtraction were read from the final positions of the beads. It was considered the first manual tool used in calculating answers to problems that provided information and in a primitive way storing the results. Abacus Mechanical Clock During the Middle Ages the first closed system in terms of calculating information was invented by use of a mechanical clock. The parts of the clock calculated the time of day. The time was displayed through the position of two hands on its face. The inventor pre-programmed the clock instructions through the manner in which the pull of the weights and the swing of the pendulum with the movement of the gears established the position of the hands on the clock face. Mathematics John Napier (Scotsman mid 1600s) discovered logarith

Secondary storage devices

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Secondary storage devices


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These are devices that store data permanently. They are classified into two categories namely: Magnet and Optical disks.

Magnetic Disks

These are disks that use magnetic technology to save data examples include:

The Hard Disk/HDD

 -A hard disk is part of a unit, often called a "disk drive," "hard drive," or "hard disk drive," that store and provides relatively quick access to large amounts of data on an electromagnetically charged surface or set of surfaces. A hard disk is really a set of stacked "disks," each of which, like phonograph/ gramophone records, has data recorded electromagnetically in concentric circles or "tracks" on the disk. A "head" (something like a phonograph arm but in a relatively fixed position) records (writes) or reads the information on the tracks. Two heads, one on each side of a disk, read or write the data as the disk spins. Each read or write operation requires that data be located, which is an operation called a "seek." (Data already in a disk cache, however, will be located more quickly.)

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Parts of the Hard Disk

 Disk platter 

  A hard-disk platter (or disk) is a component of a hard-disk drive: it is the circular disk on which the magnetic data is stored. The rigid nature of the platters in a hard drive is what gives them their name (as opposed to the flexible materials which are used to make floppy disk). Hard drives typically have several platters which are mounted on the same spindle. A platter can store information on both sides, requiring two heads per platter.

Other magnetic disks include: Zip disks, Jazz disks and magnetic tapes

Off-line/removable storage devices

Magnetic disks

Floppy disk- The term usually refers to the magnetic medium housed in a rigid plastic cartridge measuring 3.5 inches square and about 2millimeters thick. Also called a "3.5-inch diskette," it can store up to 1.44 megabytes (MB) of data. Although many personal computers today come with a 3.5-inch diskette drive pr-installed, some notebooks and centrally-administered desktop computers omit them. Floppy disk requires floppy drives (shown below) to read and write.
kcse computer notes
floppy drive(used to read floppy disks
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Parts of a floppy Disk
kcse computer notes
Floppy Disk













 Other magnetic discs include:

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Zip Disks with a capacity of 250MB
 
Jazz Disk
 
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Magnetic Tape (80MB-5TB)
 
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Magnetic Stripe (1607 bits approx: 1.4 bytes) used by credit card

 Next: Optical Disks


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