Big Brother - CD-ROM

    In this section we will talk about
"Big brother" of our beloved Speccy -
PC IBM. Despite the fact that this journal
devoted exclusively to Sinclair-compatible
machines, we believe that the proposed in this
heading information will be nebezyntersna for our
readers, moreover, it will be you very
useful. Indeed, in almost all educational institutions
IBM'y are, how many of your friends, they are
home. Discussions IBM'ovskih problems occur
often. And so when speaking of such
kind do not stand aside, saying: "This is not
for me, "You should have at-least some
minimum knowledge. We too are silent about how much
useful ideas were borrowed from IBM: mouse,
hard drive, modem, etc. etc.

    And how many more will be borrowed?

    This is the minimum we will try to give
under the heading "elder brother". And now we offer
To your attention an article about one of the most
interesting device, which is commonly
used on IBM-compatible computers ...



    Recently, the machines above 286, all
More and more often as the primary custodian
information began to use the so-called
CD-ROM.

    The fact that the same is it and how it works You
and learn from this article.

    CD-ROM (Compact Disk ROM) - continued
storage device on a compact disk that
currently the most progressive,
convenient and cost-effective carrier of information.
Why CD-ROM instead of hard drive? Because the average
capacity of a CD is 580
megabytes of data, and the cost of one disk
approximately $ 7, while the average cost
hard drive for so much information
is around 500-600 dollars.
Speed CD-ROM is much higher hard drive
so he actually called the ROM (in Russian
ROM).

    CD-ROM technology was originally
borrowed from a music CD
players, but were further developed
more advanced technologies, so our
there are three main groups of CD-ROMs.


    Consider each of the groups:



               Actual CD-ROM.


    Record on these discs is carried out
directly from the factory, and read with such
disc is a special player,
which is built into the PC. Reading from disk
possibly unlimited number of times, but
write to him nothing is impossible.

    Reading information from this disk
is done by laser, because laser has
clearly a focused beam of minimum diameter
the density of information on it is much
increases. On the drive there is only one
path spirals (as in
plate). Information, as well as on a normal
(Floppy) drive is stored in a binary system. On
Works with laser more powerful than
reads, track burnt holes, ie
as a result of record turns out that prozhzhennye
temnye place - it is zero, and the bright areas - is
unit. Bright areas called "islands" and
dark areas are called "depression."

    When reading, reading beam falls on
track, and then reflected from it falls on
analyzer. If the track "island", the beam
well reflected from it and get on
analyzer that detects the presence of the beam and give
unit. If the ray hits the "depression", she
absorb it (in physics - black color is most
absorbs light), the analyzer detects
the absence of the beam and give zero.



           Drives technology W.O.R.M.


    These disks are more progressive in
Compared with the CD-ROM'ami because on it at home
conditions can be a one time record
information. W.O.R.M. (Write Only, Read
Many) - write once, read many times.
The principle of operation is similar to CD-ROM'am, but in PC
built-in reader with an adjustable
laser power. Therefore, insert a blank mozhmo
drive to increase laser power and burn it
these same "islands", and then reduce the power
Laser and quietly read the information from it.



            Magneto-optical disks.


    These drives are the most progressive in this
time, because they can and record and
read an unlimited number of times.
The surface of the disk is covered with magnetic layer.
When recording laser beam magnetize, not
burns required track sections. Here
magnetized regions - are 'islands' and
unmagnetized - is "hollow." As is known,
magnetized regions can and demagnetized
therefore, if the information on the disk is no longer
required, then erase the disk, demagnetization at
using the same laser magnetized before
plots.



              High-speed CD-ROMs.


    Finally we want to tell about the so-called
high-speed CD-ROM'ah. The speed of the
original CD-ROMs was low, so
it is constantly increasing. CD-ROMs, imeeyuschie
multiple speeds - is nothing more than just
finalized CD-ROMs, running a few times
faster. If the CD-ROM has 8 speeds, it
does not mean that he has a
switch, changing the position of which can be
make spinning disk is faster or slower, and
means that the CD-ROM is 8 times
faster than usual.

_________________________________________________



                             A. Gardeners, 1996



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