Computer Systems:

Computer Systems: A Comprehensive Guide

Detailed chapters on fundamental concepts of computer systems. Designed for landscape viewing and print-friendly autofit.

Chapter 1: Introduction to Computers

A computer is an electronic device that processes data according to a set of instructions called a program. It performs four basic functions: input, processing, output, and storage. Computers have revolutionized every aspect of human life, from communication to entertainment, education, and business.

History of Computers

The journey of computers began with mechanical devices like the abacus (around 2400 BC) and Charles Babbage's Analytical Engine in the 19th century, often considered the first conceptual computer. The modern era started with the ENIAC in 1945, the first electronic general-purpose computer. Today, we have smartphones, supercomputers, and embedded systems.

Generations of Computers

• First Generation (1940-1956): Vacuum tubes, large size, high power consumption (e.g., UNIVAC).
• Second Generation (1956-1963): Transistors, smaller and faster (e.g., IBM 1401).
• Third Generation (1964-1971): Integrated circuits, reliable and affordable (e.g., IBM System/360).
• Fourth Generation (1971-Present): Microprocessors, personal computers (e.g., Apple II, IBM PC).
• Fifth Generation (Present-Future): AI, quantum computing, natural language processing.

Types of Computers

Type	Description	Examples
Supercomputer	High-speed for complex calculations	Fugaku, Summit
Mainframe	Large-scale data processing	IBM zSeries
Minicomputer	Mid-sized for multiple users	PDP-11
Microcomputer	Personal use	PCs, Laptops

Chapter 2: CPU and its Functions

The Central Processing Unit (CPU), often called the brain of the computer, executes instructions from programs. It consists of the Arithmetic Logic Unit (ALU), Control Unit (CU), and Registers.

Key Components

• ALU: Performs arithmetic (add, subtract) and logical operations (AND, OR).
• CU: Directs the operation of the processor, fetching and decoding instructions.
• Registers: High-speed storage locations within the CPU for temporary data.

Functions of CPU

1. Fetch: Retrieves instruction from memory.
2. Decode: Interprets the instruction.
3. Execute: Performs the operation.
4. Store: Writes results back to memory/registers.

CPU speed is measured in GHz (gigahertz), e.g., a 3.5 GHz CPU can perform 3.5 billion cycles per second. Modern CPUs like Intel Core i9 or AMD Ryzen include multiple cores for parallel processing.

Cache Memory

Small, fast memory inside the CPU (L1, L2, L3 levels) to reduce access time to main memory.

Chapter 3: Memory Types (RAM, ROM)

Memory is essential for storing data and instructions. It is classified as primary (volatile/fast) and secondary (non-volatile/slower).

RAM (Random Access Memory)

Volatile memory that loses data when power is off. Used for temporary storage during program execution.

• DRAM: Dynamic RAM, needs refreshing (cheaper, denser).
• SRAM: Static RAM, faster but expensive (used in cache).

Measured in GB (e.g., 8GB RAM allows multitasking).

ROM (Read-Only Memory)

Non-volatile, stores firmware like BIOS. Cannot be easily modified.

• PROM: Programmable once.
• EPROM: Erasable with UV light.
• EEPROM: Electrically erasable (used in flash drives).

Aspect	RAM	ROM
Volatility	Volatile	Non-volatile
Access Speed	Faster	Slower
Cost	Higher	Lower

Chapter 4: Input Devices (Keyboard, Mouse)

Input devices allow users to enter data into the computer.

Keyboard

A standard input device with keys for letters, numbers, and functions. Types include mechanical (tactile feedback), membrane (quiet), and virtual (on-screen).

• QWERTY layout is most common.
• Special keys: Function (F1-F12), Ctrl, Alt, Enter.

Mouse

Pointing device for cursor control. Optical mice use LED/light sensors; mechanical use ball.

• Buttons: Left (select), Right (context menu), Scroll wheel.
• Wireless via Bluetooth or USB dongle.

Other Input Devices

• Touchscreen: Capacitive or resistive.
• Microphone: For voice input.
• Scanner: Digitizes images/documents.

Chapter 5: Output Devices (Monitor, Printer)

Output devices display or produce results from the computer.

Monitor

Visual display unit. Measured in inches (e.g., 24-inch screen).

• LCD/LED: Liquid Crystal Display, energy-efficient.
• OLED: Organic LED, better contrast.

Resolution: HD (720p), Full HD (1080p), 4K. Refresh rate: 60Hz standard.

Printer

Produces hard copies. Types:

• Inkjet: Uses liquid ink, good for colors.
• Laser: Uses toner powder, faster for text.
• 3D Printer: Builds objects layer by layer.

DPI (dots per inch) measures print quality.

Other Output Devices

• Speakers/Headphones: Audio output.
• Projector: For large displays.

Chapter 6: Storage Devices (HDD, SSD)

Storage devices retain data permanently.

HDD (Hard Disk Drive)

Uses spinning magnetic disks. Capacities up to 20TB.

• Pros: Cheaper per GB, larger capacity.
• Cons: Slower, mechanical parts prone to failure.

SSD (Solid State Drive)

Uses flash memory, no moving parts.

• Pros: Faster read/write speeds, shock-resistant.
• Cons: More expensive, limited write cycles.

Feature	HDD	SSD
Speed	100-200 MB/s	500+ MB/s
Durability	Low	High
Cost/GB	Low	High

Other Storage

• USB Flash Drive: Portable, up to 2TB.
• Optical Discs: CD/DVD/Blu-ray.
• Cloud Storage: Online (Google Drive, OneDrive).

Chapter 7: Peripheral Devices

Peripherals are external devices connected to the computer for input, output, or storage.

Categories

• Input Peripherals: Keyboard, mouse, webcam.
• Output Peripherals: Monitor, printer, speakers.
• Storage Peripherals: External HDD, USB drives.

Connection Interfaces

• USB: Universal Serial Bus, versatile.
• HDMI: For audio/video output.
• Bluetooth: Wireless connectivity.

Peripherals expand functionality, e.g., graphics tablets for artists or MIDI keyboards for musicians.

Chapter 8: Computer Architecture

Computer architecture refers to the design and organization of a computer's hardware and software components.

Von Neumann Architecture

Classic model: Single memory for data and instructions, shared bus. Bottleneck in modern designs.

Harvard Architecture

Separate memories for data and instructions, faster but more complex (used in microcontrollers).

Key Elements

• Bus System: Address bus (location), Data bus (info), Control bus (signals).
• Motherboard: Central circuit board connecting all components.
• Expansion Slots: PCIe for GPUs, sound cards.

RISC (Reduced Instruction Set) vs CISC (Complex): ARM (RISC) for mobiles, x86 (CISC) for PCs.

Chapter 9: System vs Application Software

Software is a set of instructions that tells hardware what to do.

System Software

Manages hardware and provides platform for apps.

• OS: Windows, Linux, macOS.
• Device Drivers: For peripherals.
• Utilities: Antivirus, disk defragmenter.

Application Software

Performs specific tasks for users.

• Productivity: MS Word, Excel.
• Multimedia: Photoshop, VLC.
• Web Browsers: Chrome, Firefox.

Aspect	System Software	Application Software
Purpose	Hardware management	User tasks
Examples	OS, Drivers	Games, Editors
Developer	Usually vendor	Third-party

Chapter 10: Operating System Basics

An Operating System (OS) is system software that acts as an intermediary between users and hardware.

Functions of OS

1. Process Management: Scheduling, multitasking.
2. Memory Management: Allocation, virtual memory.
3. File Management: Organization, access control.
4. Device Management: I/O operations via drivers.
5. Security: User authentication, encryption.

Types of OS

• Batch OS: Jobs processed in batches (old mainframes).
• Time-Sharing OS: Multi-user, time-sliced (Unix).
• Real-Time OS: Immediate response (RTOS for embedded).
• Distributed OS: Manages networked computers.

Popular OS

OS	Developer	Features
Windows	Microsoft	User-friendly GUI, wide compatibility
macOS	Apple	Integrated with hardware, creative tools
Linux	Open-source	Customizable, secure, free
Android/iOS	Google/Apple	Mobile, app ecosystems

Kernel is the core of OS, handling low-level tasks.