Unit 5: Digital Representation and File Management

Key words

• BitKey word · Unit 5BitOne 0 or 1. The SMALLEST piece of computer data.Exactly: A binary digit: a single 0 or 1. It records the state of one switch, off or on.Mix-up alert: A bit is not a byte. It takes 8 bits to make 1 byte.See this in Key wordsClose meaning
• ByteKey word · Unit 5ByteA group of 8 bits.Exactly: Eight bits handled together. One byte has 256 different patterns, enough for the numbers 0 to 255.Mix-up alert: A byte is 8 bits, not the other way round. A bit is the smaller one.See this in Key wordsClose meaning
• BinaryKey word · Unit 5BinaryA way of writing numbers with only TWO digits: 0 and 1.Exactly: A number system where each place value is a power of two: 1, 2, 4, 8 and so on. Computers store all data in binary.Mix-up alert: 1010 in binary is ten. It is not one thousand ten.See this in Key wordsClose meaning
• Place valueKey word · Unit 5Place valueWhat a digit is worth because of WHERE it sits.Exactly: In binary, the columns from right to left are worth 1, 2, 4, 8, 16, 32, 64 and 128. Each column is worth double the one to its right.Mix-up alert: A 1 in the 8s place is worth 8. A 1 in the 1s place is worth only 1.See this in Key wordsClose meaning
• ConvertKey word · Unit 5ConvertChange how a number is WRITTEN without changing how much it is.Exactly: Binary to decimal: add the place values that have a 1. Decimal to binary: take the biggest place value that fits, write 1, subtract, and keep going.Mix-up alert: Converting changes the writing, not the amount. 1011 in binary and 11 in decimal are the same amount.See this in Key wordsClose meaning
• EncodingKey word · Unit 5EncodingAn AGREED RULE that gives bit patterns a meaning.Exactly: A set of rules for turning information into bits and back again. The reader must use the same encoding as the writer.Mix-up alert: Bits do not carry their meaning inside them. The same pattern can mean different things under different encodings.See this in Key wordsClose meaning
• CodeKey word · Unit 5CodeThe bit pattern that STANDS FOR one thing under a rule.Exactly: In an encoding, each letter, number or instruction gets its own pattern. In ASCII, the code for A is 01000001.Mix-up alert: Here a code is not a secret message or a program. ASCII is public, so computers that use ASCII agree on these letter codes.See this in Key wordsClose meaning
• CharacterKey word · Unit 5CharacterOne letter, digit, space or symbol in text.Exactly: A single unit of text, such as A, 7, a space or a question mark. ASCII gives each character a number code. In these activities, assume one byte per capital letter: A is 65, written 01000001.Mix-up alert: A character is not always exactly one byte in real text. When a question says "assume one byte per character", that is a rule for that question.See this in Key wordsClose meaning