Bits and Bytes

Electronic Data and Instructions Data and instructions are represented electronically Computers recognize digital signals Binary system Bit Byte Our voices recognize analog signals Continuous signals Computers only recognize digital signals Electrical On/off state The binary system consists of two digits – 0 and 1 Each 0 or 1 is called a bit – short for binary digit Bits are combined into groups of eight bits called bytes Smallest character = bit; eight bits = 1 byte or one character

Binary Coding Scheme Two state system Three types of schemes Off/on electrical states Characters represented by 0s and 1s Three types of schemes ASCII - American Standard Code for Information Exchange EBCDIC - Extended Binary Coded Decimal Interchange Code Unicode Knowing this information helps understand what takes place when data entered into computer – why it takes “so long” for the data to get transformed… Three basic schemes of coding: ASCII – primarily desktop; EBCDIC – primarily mainframe and super; Unicode – to handle languages with large numbers of characters

Data Storage in Computers an analogue quantity is one that can take any value in a range (eg the speed of my car) a digital quantity is one that can take only specific values in a range (eg my fine in Turkish Liras) a computer’s storage is a mass of tiny switches (operated electronically, not by hand) each switch can be on or off – nothing in between therefore a group of switches can represent only a finite number of values therefore data in computers is digital, not analogue

Decimal Numbers in a decimal number, each column tells how many times a particular power of 10 occurs in that number 3518 = 3 of 103 (1000) + 5 of 102 (100) + 1 of 101 (10) + 8 of 100 (1) we call the 10 possible column values digits

Binary Numbers in a decimal number, each column tells how many times a particular power of 10 occurs in that number 3518 = 3 of 103 (1000) + 5 of 102 (100) + 1 of 101 (10) + 8 of 100 (1) we call the 10 possible column values digits in a binary number, each column tells how many times a particular power of 2 occurs in that number 1011 = 1 of 23 (8) + 0 of 22 (4) + 1 of 21 (2) + 1 of 20 (1) we call the 2 possible column values bits (BInary digiTs)

Computers use binary numbers remember, computers store data in collections of switches that can be either off or on a bit, like a switch, has only 2 possible states (0 and 1) therefore a collection of switches can be seen as representing a binary number . . . off on off on on on off on (switches) = 0 1 0 1 1 1 0 1 (binary) = 93 (decimal) these are just 3 different representations of the same number

Bits and Bytes Measure storage and RAM in units of Bytes 8 bits per Byte one Byte per character eg chair = 5 bytes “K” Kilobyte (103) bytes “Meg” Megabyte (106) bytes “Gig” Gigabyte (109) bytes What is next multiple up?

Storing characters text in the computer is also stored using on/off switches using one byte (8 switches) we can encode 256 possible characters, which is generally considered to be sufficient for most applications any coding scheme is more or less arbitrary there are various coding schemes, with 2 dominant ones . . . ASCII – e.g. A, B, C is 65, 66, 67 EBCDIC – e.g. A, B, C is 193, 194, 195 Switch - either on or off state

ASCII Conversion Table Not complete but covers all the characters we are interested in…

ASCII Coding Exercise Code the following: Decipher the following: Hi fun Decipher the following: 01000001 01000101011110000110000101101101