Kilobytes, megabytes and gigabytes

Date: 2015-10-07; view: 664.

The ASCII code

Bytes and characters

1s and Os are grouped into eight-digit codes -that typically represent characters (letters, numbers and symbols). Eight bits together are called a byte. Thus, each character in a keyboard has its own arrangement of eight bits. For example, 01000001 for the letter A, 01000010 for B and 01000011 for C.

The majority of computers use a standard system for the binary representa-

tion of characters. This is the American Standard Code for Information Interchange, known popularly as 'ASC II' (pronounced 'ask-key'). There are 256 different ways of combining 0, and 1 bits in a byte. So they can give us 256 different signals. However, the ASC II code only uses 128 bytes to represent characters. The rest of the bytes are used for other purposes.

The first 32 codes are reserved for characters such as the Return key, Tab, Escape, etc. Each letter of the alphabet, and many symbols (such as punctuation marks), as well as the ten numbers, have ASCII representations. What makes this system powerful is that these codes are standard.

In order to avoid astronomical figures and sums in the calculation of bytes, we use units such as kilobytes, megabytes and gigabytes. One kilobyte is 1,024 bytes (2¹⁰) and it is represented as KB, or more informally as K. One megabyte is equivalent to 1,024 KB, and one gigabyte is 1,024 MB.

We use these units (KB, MB, GB) to describe the RAM memory, the storage capacity of disks and the size of any application or document.

Exercise 2. Lookat the illustrations and the captions below.

Then fill inthe blanks with the correct unit of memory.

Exercise 3.Word building.

AThe table gives some prefixes commonly used in computer science. Knowing the meaning of these prefixes will help you understand new words.

B Explain these expressions, taking into account the prefixes and root word.

Example: the binary system

The binary system is a notation which uses two digits, 0 and 1.

1 a minicomputer 6 a bidimensional chessboard

2 a microcomputer 7 a tricycle

3 the decimal system 8 a monochrome computer

4 the hexadecimal system 9 a CPU with 256 MB of RAM

5 a multi-user configuration 10 a document of 3 kilobytes

Exercise 4.Bits for pictures.

ARead the questions and text and study the diagrams.

Did you know that...

1 bits can also be used to code pictures?

2 the information displayed on the computer screen corresponds, dot by dot, with bits held in the main memory?

3 on colour systems, if you have 8 bits per primary colour, the palette of your computer can obtain 16.7 million colours?

Each tiny dot on the screen of a computer is called a picture element or pixel. Images and text are formed by combining a large number of pixels.

In a bit-mapped display, the dots displayed on the screen correspond, pixel by pixel, with bits in the main memory of the computer. The bits are held in an area of the memory called the 'refresh buffer' and are stored in groups, that represent the horizontal and vertical position of the pixels on the screen and whether the pixels are on or off.

Refresh buffer (memory} Display

On colour systems, each pixel is a certain combination of the three primary colours: red, green and blue. The total number of colours which can be shown on the screen is called the colour palette. The size of this palette depends on the graphics adaptor, a separate video card that converts the bits into visual signals. A graphics adaptor with 1 bit per primary colour can generate up to 8, or 2³, colours, as you can see from the table. A graphics adaptor with 8 bits per primary colour can generate 16.7 million or (2³)⁸ colours.

One bit per primary colour

BUsing the information in the passage and the illustrations, match the terms in the box with the appropriate explanation or definition.

a pixel b bit c bit-mapped display

d primary colours e palette

1 The menu of colours available on a graphics system; its size depends on the hardware.

2 Red, green and blue (RGB) in computers.

3 The smallest element of a display surface.

4 A display on the screen which corresponds, pixel by pixel, with bits stored in memory cells.

5 The acronym for 'binary digit'; one of the digits (0 and 1) used in binary notation.

CTranslate the last paragraph (starting from 'On colour systems, ...') into Ukrainian.

Do you understand the calculations made to obtain a palette of 16.7 million colours? (If you don't, ask a partner to explain them to you.)

Exercise 5. Buying a computer

Name eight different items you can buy in a computer shop.

Work with a partner. One of you wants to buy a computer, the other isthe sales assistant. Ask and answer questions, using the information and instructions below to help you.