The Business Master (4th Edition)/The Business Master - 4th Edition.iso/files/comphelp/whatvga/standard.txt

Text File | 1993-12-01 | 9KB | 258 lines

                  STANDARDS

    IBM-Compatibles are not always as
"compatible" as you might hope.  Within the
IBM-compatible field there are various
configurations of video display, memory and
peripherals (add-ons).

    By knowing about the standards and
variations, you can knowledgeably purchase
software and hardware which will work with
your system.

                     RAM

RAM stands for Random Access Memory.  This is
in the core of your computer and is used for
temporary storage of data and program
instructions as your computer is working.
    RAM is measured in bytes.  A byte is an
individual cell of 8 switches which can be
set to on or off.  This equals 256
possibilities, so any given byte can hold a
value of 0 to 255.  Characters are stored in
bytes.  For instance, the letter A is stored
in a byte as the number 65.
    A practical way to understand this is to
think in terms of a letter.  If you write a
letter that has 1500 characters in it,
including letters, punctuation and spaces, it
will require 1500 bytes of RAM to hold the
letter as you are working on it.
You need additional RAM to hold the word
processing program you are using to write the
letter.
    Large quantities of bytes are measured in
kilobytes, 1024 bytes (k), and megabytes,
1024 kilobytes (mb).

    The RAM is divided into three categories
within modern computers.  The base RAM can
contain 640k (655,360 bytes) and no more.
Computers of a few years ago had only 640k
total RAM.  Beyond the 640k base RAM, most
computers now have EMS (Expanded Memory) of
384 kilobytes, making a total of one
megabyte, and beyond that there may be a
megabyte or more of XMS (Extended Memory).

    Due to idiosyncracies in the original
design of IBM-compatible computers, and in
order to maintain compatibility with older
software, the way these three areas of RAM
are used is limited.

    Most actual processing must occur in the
base RAM (640k). Programs which use more than
the base RAM must shuffle their additional
information in and out of the base to the EMS
or XMS as needed.

    Occasionally this can mean that although
you might have 6 megabytes free, your RAM is
still all used up. Some programs will access
only the base RAM, and it is possible to pile
up several such programs, and fill up the
base memory.

    Frequent offenders are TSR and shell
programs.  TSR stands for Terminate, Stay
Resident. These programs are loaded into RAM
when first started, but remain invisible
until needed.  A typical TSR would be a
program to remind you that your mother's
birthday is tomorrow. Shells are used to
replace the user interface to DOS with
something more intuitive.  Shells list all
the programs that you can run with a nice
looking menu.  When you choose to run a
program from a menu, the shell is still in
RAM.

    Other programs manage in additional RAM
very nicely.  With these, you can do neat
tricks like storing several programs in RAM
at one time for quick switching between
programs, and you can transfer large blocks
of data between these programs.

    Some programs which are large, or work
with large amounts of data (graphics
programs, especially) are much faster if they
can work entirely within RAM.  Otherwise,
they would have to juggle data back and forth
from the hard disk as needed, and this is
much slower than shuffling it around in RAM.

    RAM is not permanently attached to the
motherboard, so you can purchase more RAM if
you wish. RAM comes in sets of chips of
varying sizes, but there are a limited number
of slots in the motherboard.  If you plug a
set of 256k RAM chips into the slots, the
motherboard may become full with a total of
2k installed. On the other hand, you can
purchase a set of 4mb chips to fill the slots
and the same motherboard will hold 32mb of
RAM.  You cannot mix chips of different
sizes, but you do not have to fill every
slot.

    Therefore, when you purchase RAM, it is
best to purchase the largest size chips you
can, since the next time you upgrade, you
might have to discard a series of smaller
chips entirely when adding more RAM if the
small ones fill all the available slots.

                VIDEO SYSTEM

Most modern IBM-compatibles come with a VGA
or better video system.  Here are the most
common types:

MDA - Monochrome text.  Monochrome means 2
colors, black and white, or often the actual
colors are black and green or amber.  This
can display text very clearly in one font
only, and has no graphics capability.

Hercules - Sometimes also called monochrome
graphics.  This combines the MDA capability
with monochrome graphics.  The resolution of
Hercules is 720 x 348. This means that up to
720 individual dots can be displayed from
left to right, and 348 vertically.  Dots are
referred to as "pixels." All graphics and
text are composed of specific arrangements of
pixels.

CGA - This is now regarded as primitive, but
it was state of the art in 1983.  CGA can
display text in 16 colors, and has two
graphics modes. 640 x 200 pixels in 2 colors
(monochrome graphics) or 320 x 200 in 4
colors.  Even the text mode uses the 640 x
200 pixel resolution which results in rather
coarse text.  With low quality monitors on
some CGA systems, it is difficult to see the
difference between an 8, a B and a 0.  Many
notebook computers use CGA, but because of
the square, well-defined pixels they display,
text is easy to read.

EGA - This is a vast improvement over CGA.
EGA has several video modes, plus it can
perfectly emulate all CGA modes and Hercules.
The best EGA mode is 640 x 350 in 16 colors.

VGA - This is even better than EGA.  It can
emulate CGA, EGA and usually Hercules.  It's
best video mode is 640 x 480 in 16 colors. It
also has a 320 x 200 256-color video mode
which is frequently used for games and
nearly photographic-quality graphics, but
because of this mode's coarse resolution, it
does not display small text well.
    Standard VGA equipment can also display
XGA modes. These are not commonly used
because programming for them is not well
documented, but some games and graphics
programs use them.  The best XGA mode is 320
x 480 in 256 colors.

Super-VGA - This can do everything that VGA
does, but goes even further.  The best common
Super-VGA mode is 1024 x 768 in 256 colors,
but this varies with brand and model of video
card and monitor.  Other modes are 640 x 400,
640 x 480, and 800 x 600 in 16 and 256
colors.  Some Super-VGA cards also support
more than 256 colors.
    Super-VGA systems come with varying
amounts of video RAM.  This is a separate set
of RAM from the main computer RAM.  The
video modes require varying amounts of RAM.
In 256-color modes, one byte is required for
every pixel shown on the screen.  In 800 x
600 mode, for instance, 480,000 bytes of
video RAM are required.
    Some software likes to have two "video
pages" available, requiring even more video
RAM.  With video pages, one page is shown on
the screen, but there can also be one or more
complete screenfuls of invisible information.
Movable graphics, animations and special
effects are created by making changes on an
invisible page, then switching it with the
visible page.
    The minimum amount of video RAM on a
Super-VGA card is 256k.  With this, not all
Super-VGA modes are possible.  The largest
common amount is 1mb. Upgrading the amount of
RAM on a video card is not usually as easy as
purchasing one with all the RAM you want in
the first place.

                 DISK DRIVES

    Hard disks can be any size, as long as
there is enough room for the software and
data you want to keep instantly available. If
your hard disk becomes full, then you can
store additional information on floppies.  A
few years ago, a 5mb hard disk was common,
and 20mb was a large model.  No matter how
big your hard disk is, you will probably fill
it within a year and wish you had something
bigger.

    Floppy disks come in two common sizes,
5.25" and 3.5".  The 3.5" disks are fully
encased in inflexible plastic, and are
becoming more and more popular. 5.25" disks
require greater care in handling and may
become obsolete in the near future.
   Both sizes come in two flavors,
"double-density" and "high-density." The high
density disks hold more information, and the
high density drives can still read data from
the older "double-density" standard.
5.25" double-density disks hold 360k of data
and 5.25" high-density disks hold 1.2mb.  In
the 3.5" disks, double-density hold 720k and
high-density hold 1.44mb.
   At the current time, almost all CD-ROM
disks and drives are interchangeable. A
CD-ROM disk holds around 650mb, but cannot be
erased or changed. This is called
"read-only."

                   MODEMS

   With a modem, you can communicate with
other computers via telephone.  Modems are
measured by the speed at which they can send
data.  This measurement is called baud, or
BPS, and roughly represents how many bits
(1/8 of a byte) can be sent per second.
Common modem speeds are 300,1200,2400,9600
and 14,400 bps.  The faster, the better.

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