1.1 Introduction to the Computer System

A computer is a programmable electronic device designed to accept data, perform prescribed mathematical and logical operations at high speed, and display the results of these operations. A computer system is the combination of all the hardware and software components that work together to make a computer functional.

• Hardware: The physical parts of a computer system that you can touch and see. This includes everything from the smallest chip to the largest monitor.
• Software: The set of instructions (programs) that tells the hardware what to do. Software is intangible.

The relationship between hardware and software is interdependent. Hardware needs software to operate, and software cannot run without the underlying hardware.

1.2 Block Diagram of a Computer

Every computer system, regardless of its size or type, follows the same basic logical structure. This structure, known as the Von Neumann architecture, can be represented by a block diagram showing the flow of data: Input -> Process -> Output.

The main components are:

1. Input Unit
2. Central Processing Unit (CPU)
3. Output Unit
4. Memory Unit (Closely associated with the CPU)

Diagram:

1.3 Input and Output Devices

a) Input Devices: These devices are used to provide data and control signals to a computer system. They translate human-readable information into a format that the computer can understand (binary).

• Keyboard: A primary input device for entering text and commands.
• Mouse: A pointing device used to interact with elements on a Graphical User Interface (GUI).
• Scanner: Converts printed documents, photographs, and other physical media into digital files.
• Microphone: Captures audio and converts it into digital data.
• Webcam: Captures video images.
• Light Pen, Joystick, Barcode Reader: Other examples of input devices.

b) Output Devices: These devices take the processed data from the computer and convert it back into a human-readable format.

• Monitor (VDU - Visual Display Unit): The primary output device for displaying text, graphics, and video.
• Printer: Creates a physical copy (hard copy) of digital documents.
• Speakers: Produce audio output.
• Projector: Displays the computer's output onto a larger screen or surface.
• Plotter: A specialized printer used for producing high-quality drawings, such as blueprints or circuit diagrams.

1.4 Central Processing Unit (CPU)

The CPU is often called the "brain" of the computer, as it is responsible for executing instructions and performing all the major processing. The speed of a CPU is measured in Hertz (Hz), nowadays typically in Gigahertz (GHz). A 3 GHz CPU can perform 3 billion cycles per second. The CPU has two main components:

1. Arithmetic Logic Unit (ALU): The ALU performs all arithmetic and logical operations.

   • Arithmetic Operations: Addition, subtraction, multiplication, division.
   • Logical Operations: Comparisons like AND, OR, NOT, and relational operations like equal to (), less than (<), greater than (>)==.

2. Control Unit (CU): The CU acts as the central nervous system for the computer. It does not perform any data processing but manages and coordinates the actions of all other parts of the computer. It fetches instructions from memory, decodes them, and directs the flow of data between the CPU, memory, and I/O devices.

1.5 Memory

Memory is the part of the computer that stores data and programs. It is organized in a hierarchy based on speed, cost, and capacity.

a) Primary Memory (Main Memory) This is the working memory of the computer, which the CPU can access directly and quickly. It is typically volatile, meaning its contents are erased when the power is turned off.

• RAM (Random Access Memory):
  • Stores the operating system, application programs, and data that are currently in use.
  • It is a read/write memory.
  • "Random Access" means any memory location can be accessed in the same amount of time.
• ROM (Read-Only Memory):
  • It is non-volatile; its contents are permanent and are not lost when power is off.
  • It contains the BIOS (Basic Input/Output System) or firmware, which includes the instructions needed to start (boot) the computer.

b) Cache Memory Cache is a very small, extremely fast, and expensive memory located between the CPU and RAM. It stores copies of the data and instructions that are most frequently used by the CPU. By providing faster access to this data, it significantly improves the overall performance of the computer system by reducing the time the CPU has to wait for data from the slower RAM.

c) Secondary Memory (Auxiliary/Storage Memory) This memory is used for long-term, permanent storage of data and programs. It is non-volatile, has a much larger capacity than primary memory, and is cheaper, but also much slower.

• Hard Disk Drive (HDD): A traditional magnetic storage device with large capacity.
• Solid-State Drive (SSD): Uses flash memory chips, has no moving parts, and is much faster and more durable than an HDD.
• Pen Drive / Flash Drive: Portable storage device using flash memory.
• Optical Disks: CD, DVD, Blu-ray discs.

d) Units of Memory The fundamental unit of memory is the bit (binary digit), which can be a 0 or a 1.