Introduction to Computer Systems

Evolution of Computing Devices

• Abacus → Pascal’s Calculator $1642$ → Leibniz Calculator $1671$ → Analytical Engine (Babbage, $1834$) → Turing Machine $1936$ → Mark I $1944$ → ENIAC $1946$ → UNIVAC-I $1951$ → Transistor $1947$ → Integrated Circuits $1970$ → VLSI $1971–80$.

Data, Processing & Information

• Data = raw facts (numbers, text, audio, video).

• Processing = operations that convert data to useful form.

• Information = processed, organised data delivered as output.

• IPO cycle: Input → Processing → Output → (optional) Storage.

Key Characteristics of a Computer

Speed (MHz/GHz), Accuracy, Diligence, Versatility, Memory, Reliability, No IQ/Feelings.

Basic Components of a Computer System

• Input Unit → devices send data to CPU.

• CPU ("brain"):
  • ALU – arithmetic/logic operations.
  • CU – fetch–decode–execute control & data flow.
  • Registers – ultra-fast temporary storage.

• Memory Unit – primary & secondary storage.

• Output Unit – presents results to user.

Input Devices (core list)

Keyboard, Mouse, Scanner, Microphone, Webcam, Barcode/QR reader, Graphics tablet.

Output Devices (core list)

Monitor/VDU, Printer (impact & non-impact, $3 ext{D}$), Speakers, Projector, Plotter.

Computer Memory

Measurement Units

$1\,\text{Byte}=8\,\text{bits}$
$1024\,\text{Bytes}=1\,\text{KB}$ → $1\,\text{MB}$ → $1\,\text{GB}$ → $1\,\text{TB}$ → $1\,\text{PB}$ → $1\,\text{EB}$ → $1\,\text{ZB}$ → $1\,\text{YB}$.

Primary (Main) Memory

• RAM (volatile):
  • SRAM – faster, costly, no refresh.
  • DRAM – denser, needs refresh.

• ROM (non-volatile): PROM (write once), EPROM (UV erasable), EEPROM/EAPROM (electrically erasable; Flash memory).

• Cache – very fast buffer between CPU & RAM.

Secondary (Auxiliary) Memory

• Magnetic: HDD (internal/external).

• Solid-state: SSD, Pen Drive, Memory Card.

• Optical: CD $700\,\text{MB}$, DVD $4.7!-!17\,\text{GB}$, Blu-ray $25/50\,\text{GB}$.

Software Categories

System Software

Operating Systems (Windows, macOS, Linux, Android), Device Drivers, Utility Programs (antivirus, backup, compression, disk repair), Language Translators.

Language Translators

Assembler: assembly → machine code.
Compiler: high-level → machine code (all at once).
Interpreter: high-level → machine code (line-by-line).

Application Software

• General Purpose – e.g., MS Office (Word, Excel, PowerPoint).

• Special Purpose – tailor-made (library, railway, hotel management, etc.).

Data Lifecycle Beyond IPO

Data Capturing → Storage → Retrieval → Deletion → Recovery.

• Storage options scale from local drives to servers/cloud.

• Common loss causes: human error, formatting, physical damage, malware, hardware failure, software corruption, theft.

• Protection: backups, passwords, encryption, secure erasure.

• Recovery tools: Norton Ghost, Symantec Backup Exec, Acronis True Image, TotalRecovery Pro.

Hardware vs Software

Hardware = physical components (internal & external).
Software = programs/instructions; requires hardware to run, hardware needs software to be useful.

Quick Facts

• Smallest data unit = bit.

• CPU speed: $1\,\text{MHz}=10^6$ instructions/s, $1\,\text{GHz}=10^9$ instructions/s.

• Cache reduces average memory access time.

• Data minimisation = store only necessary data; secure erasure removes it permanently.