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Computer Systems

Computer Systems. Nat 4/5 Computing Science Data Representation Lesson 3: Storing Text. REVISION. What is the system used to store real numbers? Convert 1100 1100 into a decimal number Convert 23 into binary. Describe what is mean by a mantissa and exponent. ANSWERS.

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Computer Systems

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  1. Computer Systems Nat 4/5 Computing Science Data Representation Lesson 3: Storing Text

  2. REVISION • What is the system used to store real numbers? • Convert 1100 1100 into a decimal number • Convert 23 into binary. • Describe what is mean by a mantissa and exponent

  3. ANSWERS • Floating Point representation • 1100 1100 = 204 • 23 = 0001 0111 • In the number 3.0 x108 the mantissa would be 3.0 with the exponent being 8

  4. Lesson Aims • By the end of this lesson you will be able to: • Describe how text is stored by the computer. • Explain and give an example of an ASCIIcharacter. • Describe how many bytes are needed to represent a single character of text. • Describe what is meant by the term character set. • Give an example of why we need different character sets.

  5. Nat 4/5 A question… • Computers can only use and understand binary digits which are 0’s and 1’s. • We have already looked at how binary can be used to store numbers. • How can we store text? • By storing them as binary numbers….

  6. Nat 4/5 ASCII Codes • Each character on a keyboard has its own ASCII code. This is a binary value that represents each character that can be seen on the screen. • American Standard Code for Information Interchange • For example A = 0100 0001 (65) • Each ASCII value takes up 1 byte of storage.

  7. Nat 4/5 ASCII Table • An extract of the ASCII Table is shown below: • The ASCII table has 128 values • 52 just for text. 10 for numbers • Spacebar and tab key have codes too • What about the rest?

  8. Nat 4/5 Control Characters • The rest of the ASCII code are reserved for control characters. • These are non-printable characters that have an effect such as • The Enter key • The delete/backspace keys • The TAB key • ALT, CTRL, SHIFT ……………………

  9. Nat 4/5 Character Set • The character set is the name given to the complete set of characters that the computer can represent. • Different character sets are used to represent different languages • The character set can alter the layout of the keyboard • For example on American layout keyboards the @ sign is above the number 2 not the “ mark.

  10. Nat 4/5 Summary • Text is stored in the computer using ASCII values • 1 ASCII Value = 1 byte of memory • Control characters are the non-printable characters which have an effect on the screen • Such as the Enter Key • The character set is the name given to the entire set of characters that the keyboard can produce

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