1. 6. Structure of Computers

2. Internal Hardware Structure
INPUT accepts instructions & data
OUTPUT communicates results to user
MEMORY stores intermediate processing results (RAM)
ALU does arithmetic (mathematical) processing and logical (relational & logical operations) processing
CONTROL UNIT (CU) controls overall operation of computer
CPU = ALU + CU
ALU
MEMORY
OUTPUT
INPUT
CONTROL

3. More about the Control Unit
The heart of a computer
Instructs input device to transfer data/instructions to main memory (RAM) then to ALU
Sends processed results from ALU to memory for storage and/or to output device
Controls flow of data as per program instructions
Coordinates ALU, memory, and peripheral units
Requires the following to operate
Instruction register: receives one by one instructions to be executed in the required sequence
Decoder: decodes the operation code & activates the appropriate circuits of the ALU to perform the operation
Address register: enables data in the location specified in the instruction to be transferred to a specified accumulator for the ALU
Instruction counter: keeps a tag on the instruction being performed

4. Input/Output Devices
See Practical 1

5. Types of Computers I Type Characteristics, Pros & Cons Analogue
Operates by measuring; graph output; calculations  equation  electronic signals; limited memory; slow; poor accuracy of output; not suited to business or industry
Digital
Use binary codes; operates by counting; functions by discrete numbers; discrete value output; high accuracy; large memory; versatile; high speed; suited for business & industry
Hybrid
Has both analogue and digital features; processes continuous and discrete data, uses converter to convert analogue data to digital data.
General Purpose
Designed to cater for varied needs.
Special Purpose
Designed to cater for specific task, e.g. Graphics and advertising make use of the Mac Pro with special graphics accelerators and monitors.
Micro
Uses micro-processors with entire CPU contained in a single chip or a few microchips; lower storage capacity vis-a-vis the mini and main frame; rate of acceptance and transfer of data is limited/ slow; uses interpreter when running high level languages; max. word length varies; small and portable; relatively inexpensive; work as soon as switched on; excellent graphic capabilities, don’t consume much power; examples desktop/PC, laptop, PDAs.

6. Types of Computers II Type Characteristics, Pros & Cons Workstation
Type of computer used for engineering, desktop publishing, software development or any application requiring moderate computing power and relatively high quality graphics capabilities; min. 64MB RAM; UNIX & Win NT; computer power between PC and minis; single user computers; normally part of a LAN;
Mini
Between the size of the micro and the mainframe; accept all high level languages; designed to serve multiple users, varied word lengths; high RAM and high memory; supports many terminals; relatively inexpensive for small/medium sized firms; high consumption of electricity; require large room space; high maintenance cost
Super
Multiprocessor systems; superior to others in capacity, function speed, accuracy and language; supercomputer channels all power to executing a few programs as fast as possible but mainframe uses its power to execute many programs concurrently (for large volumes of data processing, high performance online transaction processing systems; both use parallel processing; examples of supercomputers : Cray3. suited to weather forecasting , aircrafts design & animated graphics;
Laptop
Small mobile computer (1 to 6 kg); single main battery/ external AC/DC adapter; 3 volt cell to run the clock; can do the same work as PCs, have smaller components than other types; built-in keyboard, touchpad.

7. Conclusion: Ranking Computer Performance
Micro
Workstation
Mini
Mainframe
Super