Computer System Hardware Notes

Computer System Hardware

Introduction

• Computer Hardware: Physical parts/components that contribute to a computer system, can be felt and touched.

Inside a Computer Cabinet

• Motherboard:
  • Main circuit board.
  • Connects all computer components.
  • Houses processor and RAM.
• Central Processing Unit (CPU):
  • Performs calculations for processing.
  • Controls all parts of the computer system.
• Memory Unit (RAM):
  • Stores data temporarily to run programs.
• Storage Unit:
  • Stores data and programs permanently until deletion.
  • Examples: HDD, SSD.
• Graphics Processing Unit (GPU):
  • Processes vast amounts of graphical data.
  • Improves visual performance.
• Network Interface Card (NIC):
  • Provides a dedicated, full-time connection to a network.
• Sound Cards:
  • Generates and records audio.
  • Enables connection of speakers and microphones.
• Fans and Heat Sinks:
  • Removes heat from components to improve performance.
  • Reduces hardware component temperature.
• Power Supply Unit (PSU):
  • Takes electricity from an external source and powers the motherboard and individual hardware components.

Computer Architecture

• Design, arrangement, construction, or organization of different parts of a computer system.
• Describes what and how the computer does it.
• Components of a Computer System:
  • Input Unit
  • Processing Unit
    • Arithmetic and Logic Unit (ALU)
    • Control Unit (CU)
    • Memory Unit (Registers)
  • Memory/Storage Unit
  • Output Unit

Central Processing Unit (CPU)

• The single unit is called a processor.
• Brain of the computer, controls overall operations.
• Multipurpose, programmable, clock-driven, register-based component.
• Performs Arithmetic and Logical Operations.
• Organizes and executes instructions.
• Arithmetic and Logic Unit (ALU):
  • Performs arithmetic and logical operations.
  • Arithmetic operations are fundamental mathematical operations.
  • Logical operations are comparisons.
  • After processing, data is stored or released to an output device.
  • CPUs have multiple ALUs and FPUs that work together.
• Control Unit (CU):
  • Controls the entire operation of the computer.
  • Acts as a central nervous system.
  • Determines what task is to be performed and assigns the task for components to perform.
• Memory Unit (Registers):
  • Groups of high-speed memory within the CPU used during processing.
  • Does not perform actual processing.
  • Stores data temporarily during program execution.
  • Fastest memory.
  • ALU uses registers to store data, intermediary calculations, and results.
  • CPU registers also hold status information, program counters, or memory addresses.
• Common Register Types (Register Array):
  • Memory Address Register (MAR): Holds the address of active memory location.
  • Memory Buffer Register (MBR): Holds the contents of accessed memory location.
  • Program Counter Register (PCR): Holds the address of the next instruction to be executed.
  • Accumulator Register (AR): Holds the data to be operated upon.
  • Instruction Register (IR): Holds the current instruction being executed.
  • Input/Output Register (IOR): Used to communicate with input and output devices.

How CPU Actually Works?

• The System Clock:
  • Located on the motherboard to synchronize computer operations.
  • Sends out a signal on a regular basis (cycle).
  • Cycles per second measured in hertz (Hz).
  • One megahertz (MHz) = one million ticks of the system clock.
• The Machine Cycle / Instruction Cycle:
  • When the CPU processes a single piece of instruction.
  • Consists of four general operations:
    • Fetch
    • Decode
    • Execute
    • Store
  • Each machine cycle processes a single microcode instruction.
  • Simple commands may require multiple machine cycles.
  • Computers may need thousands, millions, or billions of machine cycles to complete a user command or program instruction.
• The Machine Cycle Example:
  • Adding 1+2 requires at least four machine cycles:
    • Step 1: Fetch number 1 from RAM, decode it, and store it in register X.
    • Step 2: Fetch number 2 from RAM, decode it, and store it in register Y.
    • Step 3: Fetch and decode the addition instruction, add the two numbers (in registers X and Y), and store the sum in register Z.
    • Step 4: Fetch and decode the instruction to display the sum, and then output the sum (currently stored in register Z) to RAM.

BUS System in Computer

• Electrically conducting path along which data is transmitted.
• Consists of a set of parallel conductors, wires, copper tracks, aluminum trails, etc.
• Each wire carries one bit at a time.
• Compared to a highway (pathways on which data travels).
• Function of Bus System:
  • Carries information from one component to another.
  • One component can interact with others by bus.
  • Supplies power to various peripherals connected to it.
• Structure of Bus System:
  • Data Bus
  • Address Bus
  • Control Bus
• Data Bus:
  • Transfers data between CPU, memory, and I/O devices.
  • May be 16-bit or 32-bit.
  • The number of wires affects the speed at which data can travel.
  • An 16 wire bus can move 16-bit at a time.
  • These lines are bidirectional (data flows in both directions).
• Address Bus:
  • Carries memory address for read & write operations.
  • The processor uses the address bus to identify peripherals or memory locations.
  • The wider the bus path, the more information can be processed at a time.
  • A 32-bit address bus can address $2^{32}$ bytes of data.
• Control Bus:
  • Carries control signals generated from the control unit within the CPU.
  • Specifies whether data is to be read or written to the memory.
  • Used to carry read/write commands, the status of I/O devices, etc.

Factors Affecting CPU Performance

• Clock Speed
• Word Length
• Cache Memory
• More RAM
• Address Bus Width
• Data Bus Width

Memory / Storage Unit

• Part of the computer system used to store data or instructions temporarily and permanently.
• Once data is stored, it remains there until replaced.

Some Terminologies

• Volatility
• Random vs Sequential Access
• Logical vs Physical Representation
• Volatile / Non-Volatile Memory:
  • Volatile memory: Requires continuous power to maintain stored data (e.g., RAM).
  • Non-volatile memory: Retains data even when power is lost (e.g., ROM, Hard Disks).
• Random vs Sequential Access:
  • Random Access: (Direct access) Data can be retrieved directly from any location, in any order (e.g., Hard drives, USB flash drives).
  • Sequential Access: Data can only be retrieved in the order it is physically stored. Slower than random access (e.g., Magnetic tape drive).
• Logical vs Physical Representation:
  • Logical file representation: User's view of data storage (filename, folders).
  • Physical file representation: Actual physical way the data is stored on the storage media as viewed by the computer.
• Memory / Storage Unit Function:
  • Storing data and instructions for short or long periods.
  • Two types of memory:
    • Primary Memory or Main Memory
    • Secondary Memory or Auxiliary Memory

Types of Memory: On the Basis of Usage

• Primary Memory:
  • RAM
  • ROM
  • Cache
• Secondary Memory:
  • Hard Disk
  • Tape Drive
  • CD, DVD
  • Flash Drives

Type of Memory: On the Basis of Technology

• Semiconductor Memory: Built using semiconductor components (transistor, IC). Ex: RAM, ROM, Cache.
• Magnetic Memory: Uses magnetic property for storing data. Ex: hard disk, floppy disk.
• Optical Memory: Uses optical property to read/write operation of data. Ex: CD, DVD, Blu-Ray Disk.

Primary Memory

• Main memory or system memory.
• Used for storing data and instructions during processing.
• Expensive, faster, and used in small storage capacity.
• Example: RAM, ROM, Cache memory.

RAM (Random Access Memory)

• Read/write memory.
• Possesses random access property; CPU can access any memory location in random sequence.
• Volatile memory; stores data as long as power is on.
• When power is off, stored content is lost.
• RAM is used to store:
  • Instruction waiting to be executed by CPU.
  • Instruction currently being executed by CPU.
  • Data waiting for processing.
  • Data currently being processed.
  • Output data.
• Types of RAM:
  • Static RAM (SRAM)
  • Dynamic RAM (DRAM)

Static RAM (SRAM)

• Stores data as long as the computer is ON.
• Faster to read/write than DRAM.
• Stores data in the form of voltage.
• Rarely used due to expensive costs and limited storage capacity.

Dynamic RAM (DRAM)

• The stored data will be lost after a few milliseconds even if the computer is in ON state.
• Cheaper but slower to read/write than SRAM.
• Stores data in the form of charge.
• A refreshing circuit is required to prevent data loss.
• Popularly used at present.

Differences between SRAM and DRAM

(This section would ideally contain a table comparing SRAM and DRAM in terms of speed, cost, storage method, etc.)

ROM (Read Only Memory)

• Can only perform read operations.
• Does not have write capabilities.
• Non-volatile memory; information stored is permanent.
• Programs in ROM include firmware, BIOS program, etc.
• Helps in booting the computer system and loading the operating system.

Difference between RAM and ROM

(This section would ideally contain a table comparing RAM and ROM based on read/write capabilities, volatility, usage, etc.)

Types of ROM

• PROM (Programmable Read Only Memory)
• EPROM (Erasable Programmable Read Only Memory)
• EEPROM (Electrically Erasable Programmable Read Only Memory)

PROM

• Programmable ROM.
• User can write data in PROM only once.
• Special equipment called ROM programmer or ROM burner is available for storing data in PROM.

EPROM

• Erasable PROM.
• Data stored in EPROM can be erased by exposing it to ultraviolet light.
• Used to store programs that are permanent but need frequent updating.
• Far more economical than PROM as it can be reused.

EEPROM

• Electrically erasable PROM.
• Can be erased and reprogrammed electrically.
• Either a single byte or the entire chip can be erased in one operation.
• It has a limit on the number of times for which it can be reprogrammed.

Flash ROM (Special type of EEPROM)

• Used in small portable computers.
• Can be inserted into slots connected to the motherboard.
• Non-volatile.
• Can be overwritten.
• Now standard on most computers today.

Cache Memory

• A special, high-speed, and expensive semiconductor memory placed between RAM and CPU.
• Used so the CPU doesn't have to wait for data to be delivered.
• Most frequently used instructions are kept in cache memory.
• Allows CPU to run faster because it doesn’t have to take time to swap instructions in and out of RAM.
• Levels of Cache Memory:
  • L1 Level
  • L2 Level
  • L3 Level

L1 Level Cache

• Smallest and fastest.
• Embedded directly into the CPU; operates at the same speed as the CPU.
• Divided into two parts:
  • L1i: Stores instructions
  • L1d: Stores data
• Size ranges from 2KB to 64KB.

L2 Level Cache

• Larger in size and slightly slower in speed compared to L1 cache.
• Located closer to the CPU than the main memory.
• Feeds data and instructions to L1 cache.
• Size ranges from 256KB to 512KB.

L3 Level Cache

• Also known as Last Level Cache (LLC).
• Larger than both L1 and L2 caches but is slower.
• Located outside of the CPU.
• Plays an important role in data sharing and communications.
• Size ranges from 1MB to 8MB.

Roles of Levels of Cache Memory

• Each level plays a crucial role in improving the performance of a computer system.
• By storing frequently accessed data and instructions, these caches help to speed up data access times and reduce the workload on the CPU.

Secondary Memory

• Additional or auxiliary memory.
• Non-volatile; used to store huge amounts of data.
• Usually cheaper and slower.
• No direct access to CPU; requires primary memory for operation.
• Example: hard disk, SSD, pen drive, etc.

Differences between Primary and Secondary Memory

Magnetic Hard Disk Drives (HDD)

• Consists of a rotating magnetic surface (platter).
• The mechanical arm (head) that moves over the platter is used to read from and write to the disk.
• The platter keeps spinning at high speed while the head of the arm moves across its surface.
• Data is stored in platters divided into tracks and sectors.