1. Logical Computer System
Unit 14, Computer Systems
Logical Computer System Presentation Unit 14

2. Logical vs. Physical
A computer system can be represented in either a logical or physical form
Both are useful in understanding Computer Systems theory.

3. Physical Computer System
The insides of a computer
The actual hardware as seen in real life
Contains micro-electronics and physical mechanisms

4. Logical Computer System
A basic model of a computer system
The model is built from a number of different blocks
Each block performs a different task
All blocks work together to process data into information
Less complex, easier to understand.

5. CPU
Control Unit
ALU
Input
Device
Main
Memory
Output
Device
Backing
Storage

6. Input Device
A device which lets the user “feed” data into the computer
Converts data into a stream of electronic digital signals
Digital signals will be converted into binary inside the computer
Some sample real-world input devices; keyboard, mouse, light pen, scanner, microphone,

7. Main Memory Stores data before being processed by CPU
Stores program being executed by computer
Is volatile - when power is removed, data is lost
Often called “RAM” - Random Access Memory
Stores processed data before it is output
Contents are filled by Input Devices, Backing Storage or the CPU
Data that needs to be saved (for future use) is written to the backing storage.

8. Backing Storage Usually mechanical (e.g. Hard Drive, CD or DVD Writer)
Data is usually “read” (loaded) or “written” (saved).
Usually non-volatile
Loads previously stored data into the main memory
Loads previously written programs into memory for processing by CPU

9. Output Devices
Converts processed data, stored in main memory, into a form that can be understood by a human as information
Some sample real-world output devices; monitor, speakers, printer, plotter, robot, etc.

10. CPU
CPU is an abbreviation of Central Processing Unit often called the Processor
The CPU is the computer’s brain
The speed of the CPU generally determines the efficiency and power of the computer system
Processors such as Pentium or AMD

11. ALU Arithmetic Logic Unit
 An ALU is an integrated circuit within a CPU  that performs arithmetic and logic operations. Arithmetic instructions include addition, subtraction, and shifting operations, while logic instructions include Boolean comparisons, such as AND, OR, and NOT operations.