The Computer
As digital hardware and software become more powerful and
less expensive, more users are able to take advantage of
technology. Understanding
technical
attributes
allows us to
more
fully utilize the computer as a tool for our purposes. Otherwise,
we run the risk of having our purposes defined by the computer.
What
we do with a computer is more important than what it does
for us.
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| Considered to be the first
modern computer, the Jacquard Loom was controlled by punch
cards. With
each throw of the loom, cards were placed in front of the
rods, allowing some to pass
through the holes, thus determining the pattern. |
From The Free On-line Dictionary
of Computing, Editor Denis Howe:
<computer> A machine that can be programmed to
manipulate symbols. Computers can perform complex and repetitive
procedures quickly, precisely and reliably and can quickly store
and retrieve large amounts of data.
Hardware
The physical components from which a computer is constructed
are known as hardware: CPU, memory and input/output.
 Central
Processing Unit
(CPU)
The CPU executes
programs ("software") which tell the computer what
to do. It is the part of the computer that controls all the other
parts. It is composed of the processor (control unit,) the arithmetic
and logic unit (ALU) and memory.
• The processor handles
data by what is referred to as the machine cycle: fetch,
decode, execute, store. (Clock speed, e.g. 2 GHz, is
one measure of processor performance.)
• The ALU performs operations
such as addition, subtraction and multiplication of integers
and Boolean
operations (AND, OR, NOT…).
• Memory includes cache,
RAM, ROM and other registers for the very fast storage and
retrieval of data. (Memory, both short- and long-term, is measured
in megabytes of gigabytes.)
While clock speed
is most commonly used to measure processing power, it is important
to consider cache size and data bus
speed (which affect throughput), as well as the chips
inherent ability to perform a number of calculations per cycle. Clock speeds are only valuable measurements when comparing
chips from the same family.
(More about the Power
Mac G5.)
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Memory
Cache
memory is
used by the processor for quick access to recently used or
frequently needed data. It
usually appears in sizes of 256k to 2 MB. Backside Level 2
cache is the fastest, while Inline and standard Level 2 are
slower,
respectively.
RAM, or Random Access Memory, is a temporary
data storage space that can be written to and read
from very
quickly
by the processor. Data stored here is volatile, however, and
once a computer crashes or is otherwise shut down, RAM contents
are
emptied.
• When a program is launched or a file opened, data
is moved from the hard drive (a relatively slow, semi-permanent
data
storage
space, discussed below) into RAM, where it can be
manipulated very quickly.
• A large amount of RAM enables the user
to
open more files and programs at the same time,
or to open larger files and perform more complex tasks. Too
little RAM can cause crashes sluggish behavior.
• As
operating
systems and applications become more advanced,
RAM requirements have increased, and luckily, prices have fallen.
Ten
years ago,
32 MB was considered a powerhouse, and cost $1500.
Today, most computers ship with a minimum 512 MB installed,
and an
additional
1 GB costs about $70.
Hard drive, the primary physical storage
unit of a computer, is a slower, more permanent form of memory.
It is usually a steel disk, coated with a magnetic recording
substrate, spinning between
read/write heads, similar to what you would see on an audio
tape deck.
• Hard drive capacity is usually measured in Gigabytes.
Current Apple desktop Mac computers
ship with 80 to 250 GB drives, while external drives
are available up to 1 TB (terabytes).
• Most drives connect
to the
CPU
by one of several common interfaces: FireWire or
USB for external, ATA for internal.
• Programs and other files installed on the computer
are stored on the hard drive, then loaded into RAM when launched.
• Documents
created by the user only exist temporarily in RAM until saved
to the hard drive.
• "Removable" drive technologies include CD-RW, DVD-RW, ZIP,
and USB "jump" drives.
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Input/Output (I/O)
I/O devices allow
the computer to communicate with the user and the outside world,
and vice versa.
Displays provide visual feedback to the user.
• New flat panel LCD screens are sharper and brighter
than the traditional CRT (tube) monitor.
• Video cards, containing their own processors and video
RAM (VRAM) control color depth and screen resolution (the amount
of data and different colors displayed,) and
the
accelerated rendering of 2D and 3D objects.
Mouse/Keyboard/Tablet Various methods of inputting text,
controlling cursors, and painting with pressure sensitive strokes.
Scanner/Camera Methods of inputting image data (pre-printed
or live).
Printer/Film Recorder/VCR Methods of outputting
data.
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