What is a Computer?; Computer System Components; Booting Process

What is a Computer?

Definition

A Computer is a machine/hardware which does different tasks for the user efficiently and effectively.

From a hardware perspective, a computer efficiently performs:

• Input — accepting data

Processing — transforming data

• Storage — saving data
• Output — presenting results
• Communication — networking

Classic 5 (now 6) Components of a Computer

Since the 1940s, computers have had 5 classic components:

1. Input Devices — Keyboard, mouse, scanner, camera, microphone
2. Output Devices — Display (monitor), printer, speakers
3. Storage Devices:
   • Volatile memory: RAM, DRAM, SRAM
   • Permanent storage: Magnetic disks, Optical disks, Flash drives (SSD)

Data Path (ALU) — Arithmetic and Logic Unit; performs computations 5. Control (ROM) — Stores firmware/BIOS; controls hardware initialization

Together, Datapath and Control are called the PROCESSOR (CPU)

6th component (modern addition): 6. Network — Essential component for communication in any computer system; connects computers globally

Block Diagram of a Computer

                   +----------------------+
                   |       COMPUTER       |
  Input    ------> | +---------+          |  ------> Output
  Devices         | | CPU     |  Memory  |          Devices
  (Keyboard,  |   | | ALU     |  (RAM)   |
  Mouse)      |   | | Control |          |
              |   | +---------+          |
              |   +----------------------+
              |           |
              +------> Network

Von Neumann Architecture

The fundamental computer architecture (Von Neumann model):

+----------+       +----------+       +----------+
|  Input   | ----> |   CPU    | ----> |  Output  |
|  Unit    |       | (ALU +   |       |  Unit    |
+----------+       | Control) |       +----------+
                   +----+-----+
                        |
                   +----+-----+
                   |  Memory  |
                   | (RAM)    |
                   +----------+
                        |
                   +----+-----+
                   | Storage  |
                   | (HDD/SSD)|
                   +----------+

Von Neumann Bottleneck: CPU is faster than memory access → limits performance.

Computer System Components

2.1 Hardware

Hardware provides basic computing resources:

• CPU — processor for computations

Memory — RAM for active data

• I/O Devices — keyboard, monitor, printer

Communication — NIC for networking

2.2 Operating System

Operating System controls and coordinates the use of hardware among various application programs for various users.

2.3 System & Application Programs

Ways in which system resources are used to solve computing problems:

• System Programs: Compiler, assembler, linker, loader
• Application Programs: Word processors, browsers, games, database systems

2.4 Users

Users can be:

• People — human users interacting via keyboard, mouse, voice

Machines — automated systems, robots

• Other computers — servers, client-server interactions

Booting Process

What Happens When We Start a Computer?

Problem: Hardware doesn't know where the operating system resides and how to load it.

Solution: Bootstrap Program

Bootstrap Program

• The initial program to run a system
• Responsible for locating and loading the OS Kernel into main memory
• Stored in ROM (Read-Only Memory) — specifically in BIOS/UEFI chip
• BIOS = Basic Input/Output System

Bootstrap Program Tasks:

• Initialize the system from CPU registers, device controllers and memory controllers
• Loads the OS kernel from a bootable device/partition
• A bootable device contains a special program called the "bootstrap loader" in its first sector (boot sector)

Bootable devices:

• Hard disk drive (HDD)
• Solid state drive (SSD)
• Pen drive (USB)

CD/DVD

Booting Process Steps

Step 1: Power On → CPU starts executing from fixed ROM address (BIOS/UEFI)
Step 2: POST (Power-On Self-Test) → hardware check (RAM, CPU, keyboard)
Step 3: BIOS/UEFI finds bootable device (using boot priority order)
Step 4: Bootstrap Loader in boot sector is loaded into RAM
Step 5: Bootstrap Loader loads OS Kernel from disk to RAM
Step 6: Kernel initializes the system (processes, drivers, filesystem)
Step 7: System is ready → login prompt (or desktop)

BIOS vs UEFI

Types of Booting