1. Bits and Bytes

2. 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

3. 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

4. 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

5. 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

6. 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)

7. 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)
= (binary)
= 93 (decimal)
these are just 3 different representations of the same number

8. 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?

9. 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

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

11. ASCII Coding Exercise Code the following: Decipher the following: Hi
fun
Decipher the following: