Computer Systems: Anatomy, Architecture, Memory & Hardware

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1. Anatomy of a Computer System

A computer system consists of hardware (physical components) and software (instructions/programs). The block diagram of a computer shows how these components interact:

Key Components:

• CPU (Central Processing Unit): The "brain" of the computer, consisting of:
  • ALU (Arithmetic Logic Unit): Performs calculations and logical operations.
  • CU (Control Unit): Manages instruction execution.
  • Registers: Temporary high-speed storage (e.g., PC, IR, ACC).
• Memory: Stores data and instructions (RAM = volatile, ROM = non-volatile).
• Input/Output Devices: Enable interaction with the user (e.g., keyboard, monitor).

A labelled diagram of a computer system showing CPU, memory, input/output devices, and their connections. (Image: Rleininger, CC BY-SA 4.0, via Wikimedia Commons)

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2. Computer Architecture

Computer architecture defines how hardware components are organized and communicate. It includes:

• Von Neumann Architecture: Uses a single memory for both data and instructions (most modern computers follow this).
• Harvard Architecture: Separates data and instruction memory (used in microcontrollers like Arduino).

Example: In a bank ATM system, the CPU processes transactions (e.g., withdrawing cash), the RAM stores temporary data (e.g., PIN verification), and the ROM holds the ATM’s operating system.

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3. Memory Hierarchy

Memory is organized in layers based on speed, cost, and capacity:

Worked Example: When you open WhatsApp on your phone:

1. The app’s instructions are loaded from SSD (L3) to RAM (L2).
2. Frequently used data (e.g., chat history) moves to CPU Cache (L1) for faster access.

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4. Types of Computers

Computers are classified based on size, speed, and purpose:

Real-World Tie-In:

• Nepal Electricity Authority (NEA) uses mainframe computers to manage grid operations and billing.
• Pathao drivers rely on microcomputers (smartphones) for real-time navigation and ride requests.

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5. System Software vs. Application Software

Worked Example: When you use eSewa to pay bills:

1. The operating system (Linux/Windows) manages the app’s resources.
2. The eSewa app (application software) processes your payment request and communicates with the bank’s server.

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6. Language Translators

Programming languages are translated into machine code using:

Example:

• WhatsApp’s backend is written in C++ (compiled) for performance.
• Python scripts (e.g., for data analysis) are interpreted for flexibility.

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7. Input/Output Devices

Softcopy vs. Hardcopy Devices

Specialized Input Devices

• OMR (Optical Mark Recognition): Used in NEB exams to read answer sheets. How it works:
  1. Students mark answers with a pencil.
  2. OMR scanner detects bubbles and converts them to digital data.
  3. Results are processed by a computer.

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8. Computer Memory (Detailed)

Primary vs. Secondary Memory

CMOS (Complementary Metal-Oxide-Semiconductor)

• Definition: A small amount of RAM powered by a battery to store BIOS settings (e.g., date/time, boot order).
• Why it matters: Ensures your computer remembers settings even when powered off.

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In the Real World

1. eSewa/Khalti (Digital Payments):

   • Uses computer architecture (CPU processes transactions) and memory hierarchy (RAM stores temporary payment data, SSD logs transactions).
   • Language translators: Backend servers use compiled languages (Java/C++) for security and speed.

2. NTC (Nepal Telecom) Network:

   • Relies on computer networks (covered in Unit 3) but starts with hardware (routers, switches) and memory (caching frequent requests in RAM).
   • Example: When you call a friend, the CPU in your phone and NTC’s servers handle the real-time data exchange.

3. Daraz Order Fulfillment:

   • Memory hierarchy: Product catalogs are stored in databases (SSD/HDD), but frequently accessed items (e.g., bestsellers) are cached in RAM for faster loading.
   • Input device: Barcode scanners (OMR-like) track inventory in warehouses.

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Exam Tip

1. Diagrams are worth marks!

   • Draw the block diagram of a computer or memory hierarchy in exams. Label every component.
   • For computer architecture, compare Von Neumann vs. Harvard in a table.

2. Define and differentiate:

   • Softcopy vs. hardcopy devices (NEB often asks for examples).
   • System software vs. application software (give 2 examples each).

3. Real-world applications score high:

   • Link memory hierarchy to WhatsApp loading chats or eSewa processing payments.
   • Explain OMR in the context of NEB exams.

4. Common pitfalls:

   • Don’t confuse RAM (volatile) with ROM (non-volatile).
   • CMOS is not the same as RAM—it’s a tiny battery-backed memory for BIOS.

5. Short-answer formulas:

   • Computer anatomy = CPU + Memory + I/O Devices.
   • Memory hierarchy = Speed ↑ → Cost ↑ → Capacity ↓.

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Visual Summary: