About data:

Our PC's are data processors. PC's function is simple: to process data, and the processing is done electronically inside
the CPU and between the other components. That sounds simple, but what are data, and how are they processed
electronically in a PC? That is the subject of these pages.

Analog data

The signals, which we send each other to communicate, are data. Our daily data have many forms: sound, letters,
numbers, and other characters (handwritten or printed), photos, graphics, film. All these data are in their nature analog,
which means that they are varied in their type. In this form, they are unusable in a PC. The PC can only process
concise, simple data formats. Such data can be processed very effectively.

Digital data

The PC is an electric unit. Therefore, it can only deal with data, which are associated with electricity. That is
accomplished using electric switches, which are either off or on. You can compare with regular household switches. If
the switch if off, the PC reads numeral 0. If it is on, it is read as numeral one. Such as a light switch. With our electric switches, we can write 0 or 1. We can now start our data processing!
The PC is filled with these switches (in the form of transistors). There are literally millions of those in the electronic
components. Each represents either a 0 or a 1, so we can process data with millions of 0's and 1's.

Bits

Each 0 or 1 is called a bit. Bit is an abbreviation of the expression BInary digiT. It is called binary, since it is derived from
the binary number system:
0 1 bit
1 1 bit
0110 4 bit
01101011 8 bit

The binary number system

The binary number system is made up of digits, just like our common decimal system (10 digit system). But, while the
decimal system uses digits 0 through 9, the binary system only uses digits 0 and 1.
If you are interested in understanding the binary number system, then here is a brief course. Try if you can follow the
system. See how numbers are constructed in the binary system, using only 0's and 1's:
Numbers, as known in the
decimal-system /
Same numbers in binary
system
0 / 0
1 / 1
2 10
3 11
4 100
5 101
6 110
7 111
8 1000

Digital data

We have seen that the PC appears capable of handling data, if it can receive them as 0's and 1's. This data format is
called digital. If we can translate our daily data from their analog format to digital format, they will appear as chains of 0's
and 1's, then the PC can handle them.
So, we must be able to digitize our data. Pour text, sounds, and pictures into a funnel, from where they emerge as 0's
and 1's, Let us see how this can be accomplished.

Bytes

The most basic data processing is word processing. Let us use that as an example. When we do word processing, we
work at a keyboard similar to a typewriter. There are 101 keys, where we find the entire alphabet A, B, C, etc. We also
find the digits from 0 to 9 and all the other characters we need:,.-;():_?!"#*%&etc..
All these characters must be digitized. They must be expressed in 0's and 1's. Bits are organized in groups of 8. A group
of 8 bits is called a byte.
8 bits = 1 byte, that is the system. Then, what can we do with bytes? First, let us see how many different bytes we can
construct. A byte is an 8 digit number. We link 0's and 1's in a pattern. How many different ones can we make? Here is
one: 01110101, and here is another: 10010101.
We can calculate that you can make 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 different patterns, since each of the 8 bits can have 2
values.
l 28 (two in the power of eight) is 256. Then there are 256 different bytes!
Now we assign a byte to each letter and other characters. And since we have 256 patterns to choose from, there is
plenty of room for all. Here you see some examples of the "translation:"

Character / Bit pattern / Byte number
A 01000001 65 ¼ 10111100 188
B 01000010 66 . 00101110 46
C 01000011 67 : 00111010 58
a 01100001 97 $ 00100100 36
b 01100010 98 \ 01011100 92
o 01101111 111 ~ 01111110 126
p 01110000 112 1 00110001 49
q 01110001 113 2 00110010 50
r 01110010 114 9 00111001 57
x 01111000 120 © 10101001 169
y 01111001 121 > 00111110 62
z 01111010 122 ‰ 10001001 137

When you write the word "summer", you write 6 letters. If the computer has to process that word, it will be digitized to 6
bytes. In other words, the word summer occupies 6 bytes in the PC RAM, when you type it, and 6 bytes on the hard
disk, if you save it.

ASCII

ASCII means American Standard Code for Information Interchange. It is an industry standard, which assigns letters,
numbers, and other characters within the 256 slots available in the 8 bit code.
The ASCII table is divided in 3 sections:
l Non printable system codes between 0 and 31.
"Lower ASCII" between 32 and 127. This part of the table originates from older, American ADP systems, which
work d on 7 bit character tables. Foreign letters, like Ø and Ü were not available then.
l
"Higher ASCII" between 128 and 255. This part is programmable, in that you can exchange characters, based on
which language you want to write in. Foreign letters are placed in this part.

An example

Let us imagine a stream of bits sent from the keyboard to the computer. When you type, streams of 8 bits are sent to the
computer. Let
us look at a series of bits:
001100010011001000110011
Bits are combined into bytes (each 8 bits). These 24 bits are interpreted as three bytes. Let us read them as bytes:
00110001,
00110010, and 00110011.
When we convert these byte binary numbers to decimal numbers, you will see that they read as 49, 50, and 51 in
decimal numbers. To
interpret these numbers, we have to look at the ASCII table. You will find that you have typed the numbers 1, 2, and 3.

About text and code

Now we have seen the PC's user data, which are always digitized. But there are many different kinds of data in the PC.
You can differentiate between 2 fundamental types of data:
l Program code, which are data, that allow the PC to function.
l User data, like text, graphics, sound.
The fact is, that the CPU must have instructions to function. You can read more about this in the review of the CPU in
module 3a. An instruction is a string of data, of 0's and 1's. The CPU is designed to recognize these instructions, which
arrive together with the user input data to be processed.
The program code is thus a collection of instructions, which are executed one by one, when the program runs. Each
time you click the mouse, or hit a key on the keyboard, instructions are sent from your software (program) to the CPU,
telling it what to do next.
User data are those data, which tells the software how to respond. The letters, illustrations, home pages, etc., which you
and I produce, are created with appropriate software.

Files

Both program code and user data are saved as files on the hard disk. Often, you can recognize the type of file by its
suffix. Here are some examples:
Content File name
Program code START.EXE, WIN.COM, HELP.DLL, VMM32.VXD
User data LETTER.DOC, HOUSE.BMP. INDEX.HTM
This is written as an introduction to naming files. The file name suffix determines how the PC will handle the file. You
can read about this subject in some of my books, e.g. "DOS - teach yourself".