Introduction to Computers

• A computer is an electronic machine
• It takes input from a user, processes it, and generates useful information as output.
• The input can be data, programs, or a user's reply to a question,
• Data is raw details needing processing, while programs are sets of instructions for the computer.
• A computer includes the CPU, monitor, keyboard, and mouse
• Key characteristics of a computer include speed, storage capacity, accuracy, reliability, versatility, and diligence.
• Limitations include "Garbage-In, Garbage-Out" and the fact that it's fundamentally a "dumb" machine.

Evolution of Computers

• Manual computing devices: Sand table, Abacus, etc.
• Automated computing devices: difference engine, analytical engine, Colossus, etc.
• Charles Babbage is considered the father of the modern computer.

Generations of Computers

• The generations: first, second, third, fourth and fifth

First Generation Computers

• Used from 1940-1956.
• Used vacuum tubes for calculation, storage, and control.
• Fastest computing devices of their time and were able to execute complex mathematical problems.
• Disadvantages: The functioning of these computers depended on the machine language, were generally designed as special-purpose computers, made them very large and bulky. Were prone to hardware faults, required cool spaces and could execute only one program at a time.

Second Generation Computers

• Used from 1956-1963
• Used transistors instead of vacuum tubes to build basic logic circuits.
• Easy to transfer, required less power, were more reliable and easier to program.
• Disadvantages: Input and output media weren't improved, needed air conditioning, costly, and were special-purpose.

Third Generation Computers

• Employed from 1964-1975
• Used Integrated Circuits
• Easily transportable, used high-level languages, easily installed, and more reliable, needed less maintenance, and were very productive.
• Disadvantages: Small storage capacity, performance degraded with large applications, high cost, and needed air conditioning.

Fourth Generation Computers

• Employed from 1975-1989.
• Used Large Scale Integration (LSI) and Very Large Scale Integration (VLSI) technology.
• The term "Personal Computer" became known at this time.
• Very powerful, large storage, reliable, user-friendly, portable programs, versatile, and required very less power.
• Disadvantages: Soldering of LSI and VLSI chips on wiring boards was difficult, and operation depended on programmer instructions.

Fifth Generation Computers

• The era of modern digital computers
• Use Ultra Large Scale Integration (ULSI) technology, allowing about ten million electronic components on a chip.
• Fastest computers to date which can execute lots of applications, small size, versatile and easy for users to use
• Versatile for communications and resource sharing

Classification of Computers

• Three ways to classify computers: operating principles, applications, and size/capability

Operating Principles

• Analog computers: represent data as continuous electrical signals.
• Digital computers: store and process data in digital form.
• Hybrid computers: combine features of analog and digital computers.

Applications

• General-purpose computers: can work in all environments.
• Special-purpose computers: perform a specific task.

Size and Capability

• Microcomputers: designed for individual use.
• Mini Computers: handle more data and input/output than microcomputers.
• Mainframe Computers: very large computers.
• Super Computers: the fastest, for complex operations at high speed.

Computing Concepts

• Raw data accepted
• Data is processed
• Data is stored
• Output is delivered

Computer System

• Hardware
• Software
• Data
• People

Computer Architecture

• Computer architecture defines the basic attributes of hardware and their interconnections
• This enables specified functions and performance

Computer Organization

• Computer organization refers to the design and physical arrangement of hardware units to achieve architectural goals.

Central Processing Unit (CPU)

• Main CPU operations: fetching instructions, decoding instructions, executing instructions, and storing results back to memory.
• CPU components: registers, arithmetic unit, logic unit, and control unit.
• Arithmetic Unit: Performs arithmetic operations (addition, subtraction, multiplication, division).
• Logic Unit: Performs logical operations on data.
• Control Unit: Controls the flow of data/info and the sequence of operations.
• Main Memory: Internal/primary memory, also known as Random Access Memory (RAM)
• Cache Memory: Small, fast, expensive memory storing frequently accessed data copies.

Registers

• Special temporary storage units within the CPU to hold instructions, data, and intermediate results.

Internal Communications

• Processor to memory communication
  • Direct communication between a computer system's processor and memory using two registers
  • Memory Address Register
  • Memory Buffer Register.
  • Reading and writing are called memory read and memory write operations
• Processor to I/O devices communication
  • Communication between input/output and a processor using an interface unit as an intermediary.

Machine Cycle

• This describes the duration of time an instruction is implemented by a processor.

Instruction Cycle

• Fetching: CPU retrieves instructions from main memory.
• Decoding: Instruction is broken down for CPU understanding.

Execution Cycle

• Executing: Decoded instruction is executed by the CPU’s Arithmetic Logic Unit (ALU).
• Storing: Results are sent either to memory or an output device.

The Bus:

• A set of wires to connect the different internal components
• Data bus: transfers data between components. Modern systems use 32-bit data buses.
• Address bus: transfers memory addresses for read/write operations.

Memory and Storage Systems

• Primary Memory: memory being handled by the CPU.
• Secondary Memory: stores results/data for future use, known as "storage".
• Internal Process Memory: Located within or near the CPU.
• Memory Representation:
• Values are represented as bits (binary digits)
• Most computers combine eight bits - a “byte”, to represent a character
• Memory is a collection of bytes/cells called a data item
• Every memory location has a numerical address, allowing the CPU to identify each cell.
• A "byte" a memory's "smallest addressable unit"
• Computers are organized into groups of 2 or 4, called "words".
• Memory is rated based on the unit of bytes
• 1 KB (Kilobyte) = 1,024 bytes
• 1 MB (Megabyte) = 1,048,576 bytes
• 1 GB (Gigabyte) = 1,073,741,824 bytes
• 1 TB (Terabyte) = 1,099,511,627,776 bytes

Random Access Memory (RAM)

• Volatile memory that is lost when there's no power.
• Main memory that stores the computer's data and allows data to be accessed in any order.
• Types of RAM: Static RAM and Dynamic RAM.
• Static RAM: Data is stored until the computer turns off. SRAM uses transistors.
• Dynamic RAM: Data is stored in a capacitor and transistor, requiring continuous refreshing; RAM is still kept after power is switched off.

Read Only Memory (ROM)

• Memory that stores data permanently.
• Data is changed, but easily read.
• Used in devices such as calculators and laser printers.
• Doesn't allow random data access, and allows data to be accessed sequentially.
• Four ROM Types
  • Programmable ROM: Write operation of data can only be performed once, used in video games and electronic dictionaries.
  • Erasable PROM: Data can be erased or destroyed using Ultraviolet Light.
  • Electrically Erasable PROM: Data can be erased or destroyed via electric charge exposure.
  • Flash ROM: Stores info with floating gate transistors, typically used in mobile phones and digital cameras.

Storage Systems

• Devices used for data storage to store data permanently.

Storage can be classified as

- Magnetic
- Optical
- Solid State
- Magneto Optical

Magnetic Storage Systems

• Use a magnetized medium with magnetized particles
• Can store any data type like text, audio, video, or images
• Include magnetic tapes, magnetic disks, hard disks, and floppy disks.

Magnetic Tapes

• Plastic tapes with magnetic coating, similar to normal recording tapes
• Data accessed using sequential access method.

Magnetic Disks

• A flat disk with magnetic coating
• Encodes info using magnetized needles
• Data is accessed randomly and allows erasing/re-recording.

Optical Storage Systems

• Use laser light to record and retrieve data.
• Devices are readable or writable.

Solid-State Storage Devices

• Developed in 1978 by Storage Tek Company.
• Don't use magnetic or optical medium; use semiconductor devices instead.
• Have hard drive properties and solid-state memory with no moving parts.
• Flash memory cards and USB devices are examples.

Storage Evaluation Criteria

• Access Mode: random, sequential, or direct.
• Access Time: processor's time to complete read/write requests.
• Storage Capacity: the memory's available size for data, measured in bytes. Storage Type: temporary or permanent.
• Cost: for the storage device to hold the data.