Hi there:
You have a really interesting question here.
WIth a long, but interesting answer.
Instead of dealing with "words" typed in to
a keyboard, I will start at the very beginning with
simple KEYS being pressed on the first IBM keyboard.
The typical "IBM" or "PC" keyboard, is, surprisingly,
an entire computer. The first keyboards offered in the
PC, the XT and the AT, had a complete microprocessor
CPU in them, with RAM, ROM, I/O, etc., which was
often MORE powerful than ENTIRE earlier, home computers !
The first PC keyboard used a CPU called the 8048, then the
8049, and clone keyboards would use any CPU they wanted,
typically, a programmable chip, ( like a 6805 series ) with a
CPU with ROM ( Read Only Memory ( to hold the instructions on how to work the keyboard ), and RAM, to store temporary keystrokes in a buffer, and I/O ( input / Output pins to send or receive the information TO or From the computer ).
The first PC used another chip on the COMPUTER end to
receive the data sent from the CPU on the keyboard, called
an 8255 PPI (Programmable Peripheral Interface ).
The first PC could ONLY SEND data from the keyboard, while
now, the Keyboard can not only send keyboard data to the
computer, but the computer can send back information, such
as TURN ON the Capitals LED light, the Number Lock,
and the Scroll Lock. As you know, there are now hundreds of
extra keys on many " multimedia " keyboards, but, the
operation is still the same -- as follows.
When you press ANY key on a keyboard, you are closing a
switch of some kind, typically a (conducting) rubber button presses on 2 traces, shorting the traces out, allowing electricity
to go across the button area, to a pin on the keyboard CPU
INPUT pins.
SInce there are 84 to 101 typical keys, and even more on the
new keyboards, this could mean that there would have to
be hundreds of buttons. To lower the traces or wires on the
keyboard, the buttons are on a grid of rows and columns.
Take an example of just a 6 row, by 10 columns grid.
There are 6 wires running from left to right, under each
key, and there are 10 rows of wires running from top to bottom.
If the rows are numbered R1 to R6,and the columns are numbered C1 to C10 from top to bottom, if a button over R1 and C1 is pressed, the CPU on the keyboard sees a short on R1/C1 ( just for example, I will call this button F1 ). The key under F1
would be the number 2, or R2/C1, and under that would be the
letter W, or R3/C1 - look at your keyboard to see what I am
referrring to. ( F1,2, W ).
The keyboard CPU has no idea what " W " or " 2 ", are, and
doesn't care. It just has a simple program that tells it,
-- IF R3/C1 switch is shorted, send a code on the wire to
the computer, HEXadecimal, 11 ( 0001 0001 in binary ). The keyboard notifies the computer that there is a character on the keyboard being sent, by interupting the Computer's CPU ( 8088 or Pentium, etc.), with IRQ 1 ( Interupt Request 1 ), and the
Computer stops what it is doing to look at the data being sent
to the motherboard's keyboard PPI 8255 chip. The data sent from
the keyboard CPU to the 8255 keyboard reciever chip is sent in
11 data bits. ( 01001001010, 11100100100, etc. ). This code
is sent, simply as zero = NO volts or ground, and " ONE " =
+5 volts -- much like morse code, or ON, OFF, ON, OFF etc,
until all the data is sent. There is one wire on the keyboard
cable that is the CLOCK PULSE, so that the " ONs" and "OFFs "
that are recieved, are at a specific time, and a code of
" Off Off Off Off, is timed into 4 specific characters, and the
8255 receiver knows there are 4 character pulses, not just one
" Off " ) The 8255, has no idea what " W " is, and does not care - it just gives the information to the motherboard CPU to take care
of. In the first PCs, the monitors were Green screen, TTL (
Transistor, Transistor Logic ) screens. All they could do was
SHOW single characters -- the first PC was designed from a WORD Processor used by Office Secretaries, so there was no need of color or graphics on typical " typewriter ".
SO, let's recap. You press a button. The keyboard CPU sees a
row and colums switch is shorted, and sends an 11 bit code for
Row3/ Column1, to the motherboard 8255 chip, and the
motherboard CPU is interuppted, and looks at the data on the
8255.
Now, the CPU has an operating system ( DOS 1, DOS 2, Windows 3.0, Windows 95, WIndows XP, etc. ), that has instructions for the CPU, when it gets keyboard code Hexadecimal 11, to " GOTO " a section of memory, in ram, and look up a set of values. In the 8088, this section of ram is a stack of 8 bit data bits.
The section of 8 bit data bits, that corresponds with code 11,
would look something like :
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 1 0 0 1 0 0 1
0 0 1 0 1 0 1 0
0 0 1 1 0 1 1 0
0 0 1 0 0 0 1 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
If you look at the arrangement of the " 1 "s in the memory
locations, you will see the letter " W ".
The motherboard CPU, takes this memory look up table, and
DUMPS the information on the Green TTL monitor, exactly as
is listed -- a " 0 " ( zero ) is a blank spot on the monitor,
and a " 1 " ( one ), is a dot.
On a blank screen, the CPU would write dots on the screen
like:
( _ is a blank, and @ is a dot )
_____________
_____________
_@___@___@
__@__@__@_
__@@_@@__
___@___@___
____________
____________
And you would see the letter " W " on the screen.
Note that neither the keyboard CPU, nor the Motherboard
keyboard receiver chip, nor the CPU, nor the monitor,
know, or care, what a " W " is. They all just work with
One's and Zero's and move the data around.
The biggest number a computer can work with, is " 1 ", ( one )
and the smallest number it knows is " 0 ", ( zero ).
The operating system tells the computer how to put dots on
the monitor screen, and how to send DOTS to a printer - that
is all. Very simple.
For modern computers, with colour and graphic pictures, the
same thing applies.There are more dots. They can be in color. Instead of using just 8 bits to hold a row of single dots ( like in the W ), each DOT can have 28 or 32 or 64 BITS-- just to say what that one little dot is ! And instead of having only a few thousand
dots on the screen, there are now millions and billions of dots on
the monitors, so that you can create complex pictures and
printing. But the same principle applies. The computer, the
keyboard and the monitor have no idea what a complicated,
colored dot pattern is - they all just move the binary bits
from one to the other.
It is really simple. Computers are simple as well ( can you
count from zero to one ? - that's all they can do ! )
Hope this helps understand how typing in a letter on a keyboard
puts the letter on your monitor in front of you, and how,
if you click on PRINT, the printer types the letter on paper.
robin