DATA REPRESENTATION - TEXT

Thought for the day: Braille Braille is a system of raised dots that can be read with the fingers by people who are blind or who have low vision. Braille is not a language. Rather, it is a code by which many languages—such as English, Spanish, Arabic, Chinese, and dozens of others—may be written and read. Braille is used by thousands of people all over the world in their native languages, and provides a means of literacy for all. Louis Braille came up with the idea of Braille in 1824 when he was 15 and frustrated with the lack of books he could read, being blind What Does Braille Look Like? Braille symbols are formed within units of space known as braille cells. A full braille cell consists of six raised dots arranged in two parallel rows each having three dots. The dot positions are identified by numbers from one through six. Sixty-four combinations are possible using one or more of these six dots. A single cell can be used to represent an alphabet letter, number, punctuation mark, or even a whole word

Big Picture – Data Representation In this topic, you need to understand: Units: bit, nibble, byte, kilobyte, megabyte, gigabyte, terabyte, petabyte The need for binary: how data needs to be converted into a binary format to be processed by a computer. How computers represent the following types of data: Numbers: binary and hexadecimal - number conversions and binary addition Images: how an image is represented as a series of pixels represented in binary Characters: the use of binary codes to represent characters Sound: how sound can be sampled and stored in digital form Compression

Learning Objectives By the end of the lesson, you will be able to: explain the use of binary codes to represent characters explain the term character set describe with examples (for example ASCII and Unicode) the relationship between the number of bits per character in a character set and the number of characters which can be represented.

Starter Using these decimal codes, what would the word Computing look like?

Starter 2 Using the character codes in the table, write a message in binary for the person sat next to you. Swap messages and ask them to decode it! Stretch & Challenge Write your message in Hexadecimal for the other person to work out

What happens when the letter C is pressed on the keyboard? Code number 67 Binary 01000011 C C button is pressed As you know, computers only understand 1&0. Humans want to read and write with letters of the alphabet. So we need a way of converting letters, known as characters, into binary which the computer can then use.

ASCII To do this, we use a character set. This is a set of characters each of which has binary code to represent each one. To save numbers and letters, computers use Ascii (American Standard Code for Information Interchange). This was developed in the late 1960s. A Character Set is the group of symbols that a computer can represent and includes letters, digits, punctuation marks and control characters. Control characters are things like Esc and Enter (aka CR because it used to be called Carriage Return). So, put simpy, ASCII is a code is where a number represents a character such as 'a' or '@' or an action of some sort

ASCII ASCII is used to allow the computer to understand the characters that have been typed in by a human. The word ‘Computing’ uses the denary codes: 67 111 109 112 117 116 105 110 103 Obviously the computer would recognise these in Binary as: 01000011 01101111 01101101 01110000 01110101 01110100 01101001 01101110 01100111 Each character is given a unique binary code and that is how the computer can represent the correct character. You will notice that each character is stored in 8 bits but only uses 7 bits. The 8th bit can be used as an addition e.g. languages where they need more characters. This is known as ‘Extended ASCII’.

ASCII Table You can use a conversion table to find out the codes for ASCII: http://en.wikipedia.org/wiki/ASCII

ASCII Facts Upper case letters have a lower binary number than lower case letters. This means that it would be true to say: A<a or c<d Ascii code uses 7 bits of data to encode up to 128 (from 0 to 127) characters. Extended Ascii code uses 8 bits of data to encode up to 256 (from 0 to 255) characters so more characters can be stored. Numbers 0-31 are for special ‘system’ codes, some of which we don’t use any more, and numbers from 128 onwards can be used on your local computer system. This means that 32-127 are common for all computer systems ever created (well since 1968). There are loads of ‘convertors’ online in case you want to convert to/from Ascii, Binary, Hexadecimal

Why ASCII? Anyone could make up a code, so why do we need ASCII? ASCII makes it possible to transfer data from one computer to another. For computers to be able to ‘understand’ each other, there needs to be a common code they understand

Using ASCII Press ALT on your keyboard and try an ASCII number on the keypad – what happens? Try numbers: 131 â 130 é 132 ä Why is this useful?

Number of bits….it’s a bit limited ASCII uses 1 byte (8 bits) to store each of the characters needed for the English language. This gives 256 possible characters which is enough for English and some European Languages. What are the limitations of this? Think about the characters you saw in the ASCII table – which languages would they cover? However what would other languages use such as Arabic or Chinese languages?

Unicode ASCII is a 7-bit set of codes that allows for 128 different characters, enough for English. Extended ASCII uses 8-bitsm giving 256 characters, enough for European languages. Unicode uses between 8 and 32 bits per character, so it can represent characters from languages from all around the world. Within the Unicode system the original 128 ACII characters still occupy the same values, so ASCII could now be considered a subset of the Unicode System for coding characters. As it is larger than ASCII, it might take up more storage space when saving documents. It would allow a user from any country to select their language when setting up an operating system. The Unicode character set would account for every language It is commonly used across the internet. Global companies, like Facebook and Google, would not use the ASCII character set because their users communicate in many different languages.

A new character set?!

ASCII Explained.... https://www.youtube.com/watch?v=JwWoVQXQ24k

Typical ASCII Exam Questions Explain how ASCII is used to represent text in a computer system. [2] What is meant by the character set of a computer? [1] Explain the possible limitations of using the ASCII character set for global communication. [4] ASCII is a 7-bit character set so can include at most 27/128 different characters. These 128 characters represent mainly just the Latin alphabet (accept English) and so this means that the characters of many other alphabets (accept languages) cannot be represented.

What to do now Log into Moodle>ICT & Computing>GCSE Computing>A451>Topic 4> Characters/Text (blue folder) > ASCII worksheet

Plenary – tell your partner…. …….the answers to these questions: What is meant by the character set of a computer? Explain how ASCII represents the character set of a computer. Explain the difference between using an ACII character set and a Unicode character set.

Plenary Answer the multiple choice quiz that has been provided. This will test how much you have learned during the lesson.