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

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

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

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.

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

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,

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.

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

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.

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

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.