Overview
of
the
Mac
19
Although
the more powerful Lisa
computer
system uses
the same microprocessor, the Mac processes
data
faster using a
7.83
MHZ*
clock as opposed
to
the Lisa's 5
MHZ
clock.
'MAC MEMORY
The
Mac
contains 128K
of
RAM memory
and
64K
of
ROM
memory.
ROM
stands for Read-Only Memory.
ROM
will hold the
data
stored in it permanently.
If
the power
to
the
Mac is
shut
off, the
information
stored in
ROM
will remain
there.
RAM
stands
for
Random
Access Memory. Any
data
stored in
RAM
will be lost when the Mac's power
is
shut
off.
THE
VIDEO DISPLAY
In
order
to
relay
information
back
to
the user, the Mac
features a nine inch, high resolution
cathode
ray tube
(CRT)
display. Its high resolution
is
due
to its 512 x 342 picture
elements (pixels) giving a total
of
175,104 individual
dots
on
the screen.
That
works out
to
about
80
pixels per inch.
The
data
for the display is stored in
about
22K
of
the available RAM.
Instead
of
recognizing letters
or
words
on
the screen, the
Mac displays
information
on
a pixel by pixel basis relying
on
the application software to provide the
proper
lettering infor-
mation. This helps reduce
both
the hardware
and
software
needed for the CRT.
The
display is black and white as opposed to the green
or
amber
and
black found
on
many
other
computers. Although
there
is
some
thought
that
the green
or
amber
displays are
easier
on
the eyes, the Mac's high resolution screen
is
very easy
to
work with and causes no discernible eyestrain.
* I
MHZ
clock generates I million clock pulses per second.
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