Bits and bytes
Computers do all calculations using a code made of just two numbers - 0 and 1.This system is called binary code. The electronic circuits in a digital computer detect the difference between two states: ON (the current passes through) or OFF (the current doesn't pass through) and represent these states as 1 or 0. Each 1 or 0 is called a binary digit, or bit.
Bits are grouped into eight-digit codes that typically represent characters (letters, numbers and symbols). Eight bits together are called a byte. Thus, each character on a keyboard has its own arrangement of eight bits. For example, 01000001 for the letter A, 01000010 for B, and 01000011 forC.
Computers use a standard code for the binary representation of characters. This is the American Standard Code for Information Interchange, or ASCII - pronounced /'aeski/. In order to avoid complex calculations of bytes, we use bigger units such as kilobytes, megabytes and gigabytes.
We use these units to describe the RAM memory, the storage capacity of disks and the size of a program or document.
Note: bit is pronounced /bit/; byte is pronounced /bait/
10,11 ,100.
One bit
Unit of memory Abbreviation Exact memory amount
|
| 10 6 |
| Example of a byte |
Complete these descriptions with the correct unit of memory.
1 A____________ is about one trillion bytes - about as much text as the books and
magazines in a huge library.
2 A .... ...._........ ...... is about one million bytes - about as much text as a 300-page novel.
3 A_................ ... is about one thousand bytes - eguivalent to one sheet of A4.
4 A...................... is about one billion bytes - about as much text as 1,000 books.
5 A ..................... can store a single character, such as the letter h or number 7.
| Inside the system |
A PC system
| 0). |
Complete this diagram of a PC system. Look at Units 1,2 and 3 to help you.
PC system
(2).
| Programs, e.g. graphics package, web browser |
| Mechanical and electronic equipment |
|
| (3) |
|
| (3) |
|
| (6). |
| ROM |
| Keyboard |
| (8). |
H
| Main memory j | |
| The'brain' of the computer |
(5)
Physical units attached to the computer
|
In pairs, compare your answers.
E5 Listen to a teacher explaining the diagram to her class and check your answers.
6 Your ideal computer system
Make notes about the features of the computer that you would most like to have. Think about the features in the box.
CPU Speed Optical disc drives Wireless connectivity Minimum/maximum RAM Monitor Ports and card memory slots Hard disk Software
В PIn pairs, describe your ideal computer system. Give reasons for your choices.