Computer systems

Outcome 1 – data representation

All data in a digital computer is stored electronically by means of groups of tiny switches which can either be ON or OFF.
A switch that is
ON has a voltage level of 5 Volts and a switch that is OFF holds a voltage level of 0 volts.

It is convenient for us to use the Base 2 (Binary) number system to consider that ON represents Binary 1 and OFF represents Binary 0 (i.e. a two state system) (Binary is the simplest number system we know)

A Binary digit or Bit as it is known, is the smallest amount of data that any computer can store.

By grouping together 8 tiny switches (Bits) it is possible to have 256 different combinations of ON's and OFF's ranging from
0000 0000 to 1111 1111. Each different combination of 1's and 0's can be a code that represents a character or symbol.

For example the character "A" is represented by the binary code 0100 0001 and "B" is represented by 0100 0010 

Data and Information :-

The key difference between data and information is that data becomes information when it makes sense to us and we can understand what it means.

What is a Data Word? :-

The Data Word size/length can be different for different computers :- a 16 bit CPU has a data word length of 16 bits while a 32 bit CPU has a data word length of 32 bits. Some large mainframe computers can have a word length of 64 + bits or more.

The data word length (in bits) and the speed of the processor (in Megahertz) provide some indication of the processing power or performance of a computer system.

Regarded as a more accurate measure of the power or performance of a computer is MOPS (Millions of Operations Per Second) or MIPS (Millions of Instructions Per Second)

Benchmarks (standard set of tasks) are used by many magazine reviewers to compare the performance of different computer systems under the same conditions.

These tasks can be used to compare the performance of the hardware and the software on different computer systems.

Benchmark results can provide the user with some guidance on the best systems to purchase for specific purposes.

There are, however, a wide range of different benchmarks available which make particular claims and it is important to look carefully at the details of what the benchmark is actually testing before placing too much emphasis on its results.

How text is represented

With ASCII, every character in a character set uses 8 bits (1 byte) so this sentence would use 104 bytes. Check it out.

With an accepted common standard such as ASCII in place, hardware and software manufacturers know that their products can almost universally be used for the transmission of data.

Due to the International nature of the Internet and the need for conducting e-commerce abroad, it has been necessary to define the Unicode standard. This is more comprehensive than ASCII to represent foreign alphabets and character sets such as Japanese and Arabic.

The Unicode consortium has defined an extensible standard (currently Unicode version 2.1). This is a 16-bit code which, in its present form, can represent up to 40,000 characters (more will be added - up to a maximum of 65,536).

Unicode-aware applications, e.g. Office 2000 allows you to edit and share documents in up to 80 different languages. There is a penalty of course, in that documents saved in Unicode format take up twice as much space as ASCII documents.

American Standard Code for Information Interchange (ASCII)  

An explanation of Hex and why we use it  

Hex is short for Hexadecimal which is the base 16 number system.

Hexadecimal uses the 16 symbols => 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F
(
A to E are needed to represent the numbers 10 to 15 as single characters)

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Example :- the binary number 1010 0111 can be written as A7 in Hex.

Like all number systems, Hex digits have place values :-

Hex <--> Binary conversions :- 

It is very easy to convert between Hex and Binary and vice versa as each character in Hex code represents 4 bits 

Binary to Hex :-
i) we can
split any binary number into blocks of 4 bits :- e.g. 1010 0111 splits into 1010 and 0111 
ii) use the
binary place values to work out the size of the number in decimal;
iii) change the number to
Hex -

Hex to Binary :- for the Hex number 3CD4 :-

i) convert each Hex character one at a time into ...

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