Computer Systems & Organization – Quick Revision

CBSE Class XI Computer Science – Units & Weightage

  • Unit 1 Computer Systems & Organization – 10 marks, 12 periods (incl. practical)

  • Unit 2 Computational Thinking & Programming – 35 marks

  • Unit 3 Data Management – 15 marks

  • Unit 4 Society, Law & Ethics – 10 marks

Core Definitions

  • Computer = electronic device → input → process → output (IPO)

  • Data = raw facts; Information = processed, meaningful data

  • Information Processing Cycle converts data ➔ information

Functional Components (Von-Neumann Model)

  • Input Unit → CPU → Output Unit; Memory shared by all

  • CPU parts: Control Unit (CU), Arithmetic Logic Unit (ALU), Registers

Memory Hierarchy & Units

  • Primary (Main) Memory: RAM (volatile, read/write), ROM (non-volatile, read-only)

  • Cache Memory: small, very fast store placed between CPU & RAM

  • Common sizes: 1 KB=1024 bytes,  1 MB=1024 KB,  1 GB=1024 MB1\ \text{KB}=1024\ \text{bytes},\;1\ \text{MB}=1024\ \text{KB},\;1\ \text{GB}=1024\ \text{MB} up to 1 YB1\ \text{YB}

Secondary Storage (persistent)

  • Magnetic — Hard Disk, Magnetic Tape

  • Optical — CD (700 MB), DVD (4.7–8.5 GB), Blu-ray (>25 GB)

  • Solid-state — USB Pen Drive, Memory Card

Communication Buses

  • Address Bus (specifies memory/I⁄O address)

  • Data Bus (carries data; width = CPU word length)

  • Control Bus (carries control signals)

Key Input/Output Devices

  • Input: Keyboard, Mouse, Light-pen, OMR, Barcode & QR readers, Biometric sensor, Touchscreen, Mic, Webcam

  • Output: Monitor/VDU (CRT, LCD), Printer (Impact – Dot-Matrix; Non-impact – Inkjet, Laser), Speakers, Plotter

Mobile System Organization (SoC)

  • CPU ≈ Applications Processing Unit (APU)

  • GPU handles graphics; ISP handles camera processing

  • Communications Processing Unit manages radio & audio (ADC/DAC)

  • Memory: Mobile RAM & ROM; Battery mAh gauges capacity

Software Categories

  • System Software → Operating System, Language Translators

  • Application Software → General-purpose (Word, Spreadsheet) & Customized (Banking, Payroll)

  • Utility Software → Antivirus, Backup, Compression, Disk Defrag, Device Drivers

  • Libraries = pre-compiled routines imported as needed (e.g. Python “math”)

Operating System Essentials

  • Interface between user & hardware; loads first after BIOS

  • Key roles: User Interface, Program Execution, Resource Allocation, File & I/O Management, Error Handling

  • Acts as Resource Manager via time & space multiplexing

Program Execution Pipeline

  • Source Code → (Assembler ⁄ Compiler ⁄ Interpreter) → Object Code

  • Loader places executable in memory

  • Linker combines object code with libraries to form final executable

Language Translators

  • Assembler: Assembly → machine code

  • Compiler: translates & optimises whole program at once; errors reported after compile

  • Interpreter: translates & executes line-by-line; stops at first error

Cloud Computing

  1. Delivers IT resources over Internet: IaaS, PaaS, SaaS, DaaS

  • Deployment: Public Cloud (shared), Private Cloud (dedicated)

Parallel Computing (Why?)

  • Splits problem into parts executed concurrently across multiple cores → saves time, solves larger problems, utilises hardware fully

Quick-Recall Equations & Facts

  • 8 bits=1 byte8\ \text{bits}=1\ \text{byte}, 4 bits=1 nibble4\ \text{bits}=1\ \text{nibble}

  • Addressable locations with nn-bit address bus = 2n2^{n}

  • SoC = CPU + GPU + ISP + Radio Processor on single chip

  • IPO Cycle ⇨ Input → Processing → Output