Today's computers can perform more than 500 million operations per
second and store hundreds of millions of characters in memory. Early
computers were very large and very slow compared to modern personal
computers. They weighed as much as 30 tons and occupied over a
thousand square feet. Their size was due to the many vacuum tubes
which you may have seen in old radios or TVs. Today these tubes have
been replaced by tiny transistors and silicon chips.
A computer is much like the human nervous system. The sensory
nerves (touch, smell, taste, sight, hearing) serve as input units for
the brain. The brain takes the information from the sensory nerves,
such as the smell of a pepperoni pizza and transfers it to the brain
where it is processed so that the brain knows what the aroma is by
comparing to other known smells which it stores in memory! Finally,
the brain sends the information to the output unit which in this case
is the mouth which allows the person to say, "That sure must be good
pizza! Could I have some?"
The keyboard is used as an input device which means that you can
"talk" to the computer by typing information from the keyboard to the
central processing unit (cpu) which decides exactly what to do with
the information you have given it. The mouse (beside the keyboard) is
used to choose items on the screen or monitor. The central processor
can send the information to the monitor or the printer which serve as
output devices where you can see what the computer has done for you!
If you do not want to lose the information the computer has in memory
(RAM) , you can use the hard drive and zip disk for a storage
device.
BITS, BYTES, KILOBYTES (KB), MEGABYTES (MB) and GIGABYTES
(GB)
It is important to know a little bit about how sophisticated the inner workings
of a computer are, even though you may never need to work at this level. Behind
all the activities we do with computers, there are microprocessors and chips
made up of microscopic transistors. These transistors control whether electricity
can flow or not flow in a circuit. It is much like a ON/OFF switch in your home.
The computer is not smart enough to understand numbers or words, but it does
understand when electricity is flowing or not flowing. We represent this fact
by using the binary number system which is made up of two digits - 0 and 1 (0
for no current and 1 for current). These 0's and 1's are called bits. To represent
letters or other symbols, we use eight bits which together are called a byte.
So the letter A would be represented by the following binary number 00110000
! One thousand bytes or one thousand characters is called a kilobyte, KB, or
K. Most computer use megabytes (MB) and gigabytes (GB) to measure the storage
capacity of disks and the amount of memory available. A Megabyte is one million
bytes, and a Gigabyte is one billion bytes.
ROM and RAM |
There are two major types of chips found on the main circuit board
of the computer. There is Read Only Memory (ROM) which is the part of
the computer which you cannot change and which allows the computer to
display information on thescreen and direct your work to the proper location.
Your work on the computer is stored in Random Access Memory (RAM) which
is memory that can be changed and holds your programs and written work.
If the power goes off, the contents of RAM are erased and all the information
there is lost. This is why it is necessary to save your work on a hard
disk or zip disk for more permanent storage. But the ROM is permanent
and will be restored when the power is returned.
If you want to learn how much RAM is available and in use on your computer,
you can choose "About this Mac" under the menu that looks like an apple
on the top left corner of the screen. If you choose that menu item, you
will get a picture like the one on the left side of the screen.
This computer is running Macintosh operating system version 10.4.3. and
has 512MB of RAM. |
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PERMANENT STORAGE |
When you quit from an application program like Appleworks
or Internet Explorer, the contents of the RAM that was used to run that
program is reused. If you want to store something that will be there the
next time you start the computer, you must use permanent storage. The
hard disk drive (or hard drive) on your computer can store permanently
(almost!) the contents of your files and the application programs that
created your files.
The hard drive "Macintosh HD" shown in the picture below has 11 items
stored in it with 20.76 Gigabytes (billion bytes) remaining.
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Assignment
1. How is a computer similar to the human mind and body. Give
specific examples.
2. What are the input and output devices found on a computer. Be
specific.
3. What do the letters in ROM and RAM stand for? What is stored in
each?
4. Give your understanding of bits, bytes, kilobytes, megabytes
and gigabytes.
5. Look at a computer in the computer lab and write down a) the ID
number of that computer, (the piece of paper glued to the station
with a number printed on it) b) how many bytes are available on the
hard drive and c) the amount of built-in RAM and Virtual memory
available for that computer.