1. How Computers Work
Part 1
6 February 2008

2. Sometimes They Don’t
Having a Bad Day
Mouse Won’t Work

3. Simplified Model of a Computer
processor
retrieves the
instruction
directs data movement
Performs the operations
Control Unit
Arithmetic Logic Unit
instructions
data
the information that it works on
defines an algorithm
MEMORY

4. Computer Cycle
Fetch
Execute
Store

5. Logical organization of computer system
CPU
Inputs
Outputs
programs
data
Memory
information
Programs &
Data/info in use now
Storage
LOTS of programs and data files stored here

6. Simplified Model of a Computer
processor
retrieves the
instruction
directs data movement
Performs the operations
Control Unit
Arithmetic Logic Unit
instructions
data
the information that it works on
defines an algorithm
MEMORY

7. Binary System 1 = Everyone knows that computers store bits, right?
What does it mean?
All data is stored as a series of zeroes and ones
Why? 1 =

8. Representing Numbers Additive system Positional system ||||| |||||
Every item represents 1
Examples of additive systems?
Positional system
Value = face * place
37 = 3*10 + 7*1
||||

9. Positional System Base = number of different values in a position
Base 10 = 10 values: 0-9
Base 2 = 2 values: 0-1
Value of each position = power of base
b4 b3 b2 b1 b0
Binary:

10. Binary Positional System= 1 2 3 4 1 =

11. Examples
Examples
1111 = 15
1000 = 8 =
100

12. Exercises
Find the decimal value of
1111
10111

13.
(place value) =0 =1 =2 =3 =4 =5 =6 =7 =8 =9
=10
=11
Etc.

14. Making sense? 26 25 24 23 22 21 20 64 32 16 8 4 2 1 (place value)
(place value)
Represent 37 in binary code?
What about 63?

15. Exercises
Find the decimal value of
1111
10111

16. Decimal Numbers represented logically in binary form
represented physically with bits

17. Data Types
Computer doesn’t know what the bits represents or what format is being used
Computer assumes that the instructions know the format of the data
What are the types of data?
Numbers, text, pictures, sound, instructions

18. Data Types
Numbers: integers and floating point numbers (scientific notation)
Why do we need floating point numbers?
Text: Unicode, double byte
Languages and symbols (Word insert symbol)
Pictures: pixels
A very fine needlepoint
How to represent color?
Sound: different formats
Instructions