Computers
as a Second LanguageComputers
as a Second LanguageComputer Fundamentals
HOW
DO DISKS WORK? You
may recall an elementary school experiment where you took an ordinary
nail and placed it near some iron filings. Nothing happened. Then you
placed a magnet onto the iron filings and thousands of them stuck to the
magnet. Next you peeled the iron filings off the magnet and placed them
onto the table well away from the magnet. Using the same nail as before,
you brought the nail up to the iron filings. Presto, the iron filings
jumped onto the nail because they were magnetized. They became instantly
magnetized just by touching a magnet! This happened because iron filings
are very fine and possess a tremendous surface area which facilitates
them becoming magnetized.A
disk works on exactly the same principal. The microscopic-sized iron
particles are magnetized by the electromagnetic head of the disk drive.
When a disk drive records computer information onto a disk, it is simply
duplicating the settings of the switches as they are set in RAM at the
time of recording. For example, if the first byte in RAM to be recorded
contains 8 bits with the switches sitting as
ON-ON-OFF-OFF-OFF-ON-OFF-ON, the disk drive head will record onto the
disk, MAGNETIZE - MAGNETIZE - DO_NOT_MAGNETIZE - DO_NOT_MAGNETIZE -
DO_NOT_MAGNETIZE - MAGNETIZE - DO_NOT_MAGNETIZE - MAGNETIZE. Each byte
is successively recorded like this.As
noted earlier, when you turn a computer on, all the RAM switches are
initially off. This means the computer has no instructions to follow and
is basically useless. The way to make a computer useful is to load the
RAM with some instructions, called software. Software
instructions (computer programs) are pre-recorded onto
a disk by the manufacturer of the software. When the disk is inserted
into the disk drive, the program is copied into the computer's RAM. The
disk drive reads every bit of magnetic information on the disk and sets
the RAM switches exactly as it reads them. If the first 8 bits of
magnetic information on the disk said, "I'M_MAGNETIZED -
I'M_MAGNETIZED - I'M_NOT_MAGNETIZED - I'M_NOT_MAGNETIZED -
I'M_NOT_MAGNETIZED - I'M_MAGNETIZED - I'M_NOT_MAGNETIZED -
I'M_MAGNETIZED", the first byte in RAM would be set as,
ON-ON-OFF-OFF-OFF-ON-OFF-ON. That is all there is to it!Hard
disk drives can store tremendous amounts of computer information. It is
important that this information can be quickly accessed and transferred
to the computer's RAM. The average amount of time it takes a hard disk
drive to access any data is measured in milliseconds (MS) or thousandths
of a second. The faster the access time, the better. A hard disk drive
with an average access time of 10 MS is superior to one with an access
time of 40 MS. These times may all seem incomprehensibly fast, however,
when you use a computer for graphics intensive applications which
involve vast amounts of data, these access times become very important. |
