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BASIC COMPUTER ORGANIZATION

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BASIC COMPUTER ORGANIZATION

Over the several years the size, processing speed, cost and reliability of computers has changed. But, the basic structure of computer is still the same as was given by Von Neumann in the year 1945 has not changed. According to Von Neumann architecture of computer every digital computer with these components:

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BASIC COMPUTER ORGANIZATION

  • 1. Input Unit
  • 2. Output Unit
  • 3. Memory Unit
  • 4. Arithmetic Logic Unit
  • 5. Control Unit

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Basic Computer Organization

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INPUT UNIT

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  • The input unit is responsible for receiving data and instructions from the outside world (like from a keyboard, mouse, scanner, or microphone). It converts these inputs into binary data (0s and 1s) that the computer’s CPU can understand.

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OUTPUT UNIT

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  • This unit takes the processed data from the computer and converts it into a form understandable to humans (text on a screen, printed paper, sound, etc.).

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3. CENTRAL PROCESSING UNIT (CPU)���

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  • Arithmetic Logic Unit (ALU):

Place where the actual instruction take place during the processing operations�Performs all mathematical calculations (addition, subtraction, multiplication, division) and logical operations (comparisons like greater than, equal to).

  • Control Unit (CU):
  • It acts as central nervous system for the other components of computer
  • It manages and coordinates the entire computer system�Directs the flow of data within the computer. It interprets the instructions from memory, signals the ALU to perform operations, and manages communication between the CPU and other units.
  • Executes program instructions by fetching them from memory, decoding, and then executing

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4. MEMORY UNIT���

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  • Primary Memory (Main Memory):
    • RAM (Random Access Memory): Temporarily stores data and instructions that the CPU is currently using. Data is lost when the computer is turned off.
    • ROM (Read-Only Memory): Stores permanent instructions like the BIOS that start the computer.
  • Secondary Memory:
    • Hard drives, solid-state drives, USB drives, CDs — used for long-term data storage.

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PRIMARY MEMORY (MAIN MEMORY):

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SECONDARY MEMORY�

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SYSTEM BUS�

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  • The system bus is the common communication path that carries signals to/from the CPU, main memory and input/output devices.
  • Types of Buses:
    • Data Bus: Transfers actual data. The data bus carries data from one component to another,
    • Address Bus: Transfers information about where data should go. The address bus carries the address location of the data or instruction
    • Control Bus: Transfers control signals to coordinate operations. control bus carries the control signals. 
  • Connects CPU, memory, and I/O devices, allowing them to communicate and transfer data.

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SYSTEM BUS

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I/O Device

Subsystem

Address Bus

Data Bus

Control Bus

CPU

Memory

Subsystem

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MEMORY UNIT

UNIT

VALUE

1 Bit

1 Bit=(0,1)

Nibble

4 bits

Byte

8 bits

Kilobyte(KB)

1024 Bytes or 2 10

Megabyte(MB)

1024 KB or 2 20

Gigabyte(GB)

1024 MB or 2 30

Terabyte(TB)

1024 GB or 2 40

Petabyte(PB)

1024 TB or 2 50

Exabyte(EB)

1024 PB or 2 60

Zetttabyte(ZB)

1024 EB or 2 70

Yottabyte(YB)

1024ZB or 2 80

Brontobyte(BB)

1024YB or 2 90

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WHAT IS CACHE MEMORY

  • Cache memory is a small, high-speed memory located close to the CPU that stores frequently accessed data and instructions.
  • It acts as a buffer between the CPU and main memory (RAM), helping the CPU access data much faster than it could from RAM alone.

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WHY IS IT IMPORTANT?

  • Accessing RAM is slower than accessing cache.
  • The CPU is very fast and needs data quickly — cache reduces the delay (called latency) by keeping recently or frequently used data nearby.

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CACHE MEMORY

  • Speed: Cache memory is significantly faster than RAM, allowing the CPU to access frequently used data much more quickly.
  • Location: It can be located directly on the CPU or situated between the CPU and main memory.
  • Size: Cache memory is smaller in capacity compared to RAM.
  • Purpose: It stores data and instructions that the CPU is likely to use again, reducing the need to access slower main memory.
  • Levels: Cache memory often comes in multiple levels (L1, L2, L3), with L1 being the smallest and fastest, and L3 being the largest and slowest among them.

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TYPES OF CACHE MEMORY:

  • L1 (Level 1) Cache:
  • L2 (Level 2) Cache
  • L3 (Level 3) Cache:�

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L1 (LEVEL 1) CACHE:�

  • Smallest and fastest

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  • Located inside the CPU core

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  • Typically 32KB to 128KB

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L2 (LEVEL 2) CACHE:�

Larger but a bit slower than L1

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Can be inside or just outside the CPU core

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Usually 256KB to a few MB

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L3 (LEVEL 3) CACHE:�

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  • Shared among multiple cores

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  • Larger and slower than L1 and L2

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  • Several MB in size (e.g., 8MB, 12MB)

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HOW CACHE WORKS:

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  • When the CPU needs data:

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  • It checks L1 cache first.

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  • If not found, it checks L2, then L3.

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  • If still not found (called a cache miss), it fetches from RAM, and possibly stores it in cache for future use.

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CACHE MEMORY

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REGISTERS

  • A central processing unit (CPU) is the brain of a computer system that carries out all the instructions and calculations necessary for the functioning of the system.
  • Within the CPU, there are various components that facilitate the execution of these instructions, and one such crucial component is the register.
  • Registers are small, high-speed storage units that play a vital role in the overall functioning of the CPU.

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INSTRUCTION REGISTER(IR)

  • The instruction register (IR) is a register in the CPU that stores the current instruction being executed.

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  • It holds the binary code of the instruction fetched from the memory and is responsible for decoding and executing that specific instruction.

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PROGRAM COUNTER(PC)

  • Program Counter (PC) is used to keep the track of the execution of the program.
  • The program counter (PC) is a specific type of register that stores the address of the next instruction to be fetched from memory.
  • It points to the memory location where the next instruction resides.
  • The PC is automatically incremented after each instruction is fetched to point to the next instruction in the sequence

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ACCUMULATOR REGISTER(AR)

  • Accumulator : This is the most frequently used register used to store data taken from memory. 
  • An accumulator is a register, or a memory location used to store the intermediate results of arithmetic and logical operations.
  • It plays a crucial role in performing calculations and processing data in various applications.

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MEMORY ADDRESS REGISTERS (MAR) :

  • Memory Address Registers (MAR) : It holds the address of the location to be accessed from memory. MAR and MDR (Memory Data Register) together facilitate
  • A Memory Address Register (MAR) is a CPU register that holds the memory address of the data or instruction that the CPU needs to access. 
  • It acts as an intermediary between the CPU and memory, enabling the CPU to read from or write to specific locations in memory

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MEMORY DATA REGISTERS (MDR) 

  • Memory Data Registers (MDR) : It contains data to be written into or to be read out from the addressed location.

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Registers | <- Smallest size, fastest access (nanoseconds)

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| Cache | <- Small, very fast (few KB to MB)

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| RAM | <- Larger, slower (GBs)

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| Disk | <- Much larger, slowest (GBs to TBs)