Computer Architecture – Overview of Computer Systems 2

Definition & Core Workflow of a Computer

• A computer is a programmable electronic device that:
  • Receives input (raw data)
  • Processes data under a stored set of instructions (program)
  • Produces output (information)
  • Stores and communicates data
• Simplest workflow:
  1. Input → 2. Processing ↔ (temporary) Storage ↔ Feedback → 3. Output → (optional) permanent Storage
• Four basic functions
  • Input – user enters data
  • Process – arithmetic & logical operations are executed
  • Output – results are returned as information
  • Storage – data/ information kept either temporarily (RAM) or permanently (e.g. SSD)

Characteristics of a Computer

• Processing speed: executes millions of instructions per second; measured in $\text{Hertz (Hz)}$
• Storage power: huge capacity in small space; memory measured in bytes ( $1\;\text{byte}=8\;\text{bits}$ )
• Accuracy: extremely high; most errors are human-originated
• Diligence: no fatigue; consistent results
• Versatility: suitable for diverse tasks (e.g. gaming, simulation, accounts)
• Reliability: can repeat tasks for long periods without failure

History of Computers (Generations)

Zeroth Generation – Mechanical / Pre-electronic

• Jacquard Loom (1801): first stored program (metal punched cards)
• Difference Engine (1822): steam-powered calculator (unfinished)
• Analytical Engine (1833): could store numbers, accurate to 6 decimals; steam & punched cards

1st Generation – Vacuum Tube (1940s–1950s)

• 18 000 vacuum tubes, magnetic drum, punched cards, machine language
• Large, expensive, high heat, millisecond speeds
• Examples: ENIAC, UNIVAC

2nd Generation – Transistor (1950s–1960s)

• Magnetic tape, punched cards, assembly language
• Smaller, faster (µs), less heat, lower cost
• Examples: IBM 7000, Mark III, ATLAS, NCR 304

3rd Generation – Integrated Circuit (1960s–1970s)

• Hard disks, keyboards, mouse, operating systems, high-level languages
• Nanosecond speeds, further miniaturisation
• Examples: IBM 360 series, Honeywell 6000, TDC 316

4th Generation – LSI & VLSI (1970s–present)

• Microprocessors, GUIs, C/C++/Java, networking
• Examples: IBM 4341, Apple II

5th Generation – ULSI, Present & Beyond

• Advanced GUIs, AI, machine learning, parallel processing, visual programming
• Examples (form factors): laptops, desktops, tablets, mobiles

Possible Next Generations

• Quantum computing: superposition-based qubits
• Nano computing: <100\,\text{nm} transistors
• Biological computing: DNA & protein logic

Components of a Computer System

A complete system = Hardware + Software + Data & Information + Users/People + Procedures

1. Hardware

System Unit

• Motherboard – main circuit board connecting all components
• CPU – executes instructions, controls other parts
• RAM – temporary data/instruction store while working
• Storage – HDD, SSD, flash; permanent data store
• Drives/Bays – house optical drives, disks
• Power Supply – converts AC → DC used by system
• Cooling (Fan/Heatsink) – dissipates CPU heat
• Expansion Slots/Cards – add new capabilities (GPU, NIC, etc.)
• Ports & Connectors – USB, HDMI, Ethernet

Input Devices (4 classes)

• Text-input: keyboard, barcode scanner (text mode)
• Pointing: mouse, trackpad, joystick
• Scanning: flatbed scanner, QR reader
• Visual & Audio: webcam, microphone

Output Devices

• Soft-copy: monitors, VR headsets, speakers
• Hard-copy: printers, plotters, 3-D printers

Communication Devices

• Router, switch, hub, modem, repeater, firewall, gateway; allow data/resource sharing

2. Software

Application Software

• Performs specific user tasks
• Two categories:
  • Web-based (runs on server, accessed via browser): Google Docs, WhatsApp, Gmail, Netflix
  • Stand-alone (local install): MS Word, Adobe Photoshop, CorelDraw

System Software

• Controls & manages hardware so everything runs smoothly
• Operating Systems: Windows, Linux, macOS, Android, iOS
• Utility Software: antivirus, compression tools, disk management, device drivers, language translators (compiler/interpreter/assembler)

3. Data vs. Information

• Data = raw, unprocessed facts (e.g., Name, DOB, Phone #)
• Information = organised/presented data in meaningful way (e.g., “Customer Details” record)

4. People

• End-users: students, lecturers, accountants, customers
• IT specialists: system analyst, programmer, network admin, database admin

5. Procedures

• Documented rules/guidelines for using hardware, software & data; provided via manuals (print/electronic)

Computer Architecture & System Unit Internals

• Layered view:
  1. Hardware ↔ 2. Device Drivers ↔ 3. System Utilities (OS kernel, file system) ↔ 4. Operating System ↔ 5. Application Programs ↔ 6. User
• Block diagram:
  • Input Unit → CPU (Control Unit + ALU + Registers) ↔ Memory Unit ↔ Output Unit
• CPU sub-units
  • Control Unit (CU) – orchestrates fetch–decode–execute cycle
  • ALU – arithmetic ($+,-,*,/$) & logical ($<,>,=,\land,\lor$) ops
  • Registers – fast internal storage (accumulator, PC, IR)

How Computers Work (Illustrative Example)

Task: flip a photo in an editor

1. User moves mouse → input instruction “Flip”
2. Image represented as pixels/bits; program reverses bit order (left ↔ right)
3. Result placed in RAM & rendered on monitor (output)
4. If “Save”, data written to permanent storage (HDD/SSD)

Types of Computers & Comparative Attributes

Usage Examples

• Supercomputer: nuclear simulations, weather forecasting, MMORPG servers (e.g., WoW)
• Mainframe: banking ATMs, airline reservation, e-business records
• Minicomputer: manufacturing control, lab equipment, small business servers
• Microcomputer: desktops, laptops, tablets, smartphones, workstations

Recap & Exam Preparation Pointers

• Master timeline & traits of all five generations
• Know basic functions & characteristics of computers
• Be able to sketch/label system-unit diagram & block diagram architecture
• Distinguish hardware vs. software vs. data vs. people vs. procedures
• Compare computer types by speed, capacity, cost, and example uses
• Next class will cover data representation; revise binary, decimal, octal, hexadecimal & bring calculators