Computer organisation

SUDHARSAN R

hardware

Input
Unit

Output
Unit

Storage
Unit

Memory

Arithmetic / Control
Unit

Communication Bus

Input Unit

OUTput Unit

STorage unit

Non-volatile storage - data is retained even when power is turned off

Memory

• Volatile Storage - data is lost when power is turned off
• All working data is brought from storage and placed in memory
• Number of pins on the chip determine data transfer capacity

Arithmetic / Control Unit

• Commonly referred to as processor
• Arithmetic Unit
  • Integer computations
  • Floating-point computations
• Control Unit
• Registers - high-speed (1 cycle) scratchpad memory, which can store temproary data values
• Cache memory - fast (2-10 cycles) storage inside the processor, access slower than register

computation theory

• A program is a sequence of instructions which perform a certain computation
• Each instruction consists of
  • operation to perform
  • operands (data values) on which operation should be performed
• eg program: c = 2 * a + b; Instructions:
  • x <- 2 * a
  • y <- x + b
  • c <- y
• Here, a, b and c are data values or data, which the program operates on

von neumann architecture

Communication

Channel

Processor

Memory

• Both program and data are stored in memory
• Instructions and corresponding data are fetched from memory before execution; output stored back
• Any computation can be expressed as a sequence of instructions - distinguishes computers from other machines

performance

• Processors
  • Extremely fast - Intel Core i9 works at 3GHz
  • Each processor chip usually contains multiple processors
  • Each processor contains multiple arithmetic units
• Memory
  • Relatively slower : ~800MHz
  • Limited by number of pins on memory chip
  • Overall performance is bottlenecked by memory - memory is not able to provide sufficient data values to keep the processor always busy

Solution: Hierarchy of memories!

types of memory

• Main Memory - RAM
• Non volatile Memory - Hard disk / SSD
• Register
  • ​scratchpad memory located closest to arithmetic unit
  • fastest memory access
• Cache
  • ​small memory located inside the processor
  • value fetched from main memory is stored here for access in the future
  • faster than main memory but slower than register

Memory hierarchy

1 cycle

Capacity

Speed

2-10 cycles

~200 cycles

1000s of cycles

8-16

16-32KB

~GBs

~TBs

Register

Cache Memory

Main Memory (RAM)

Hard-disk / SSD

Processor

software

• System Software
  • Operating system - Android, Windows
  • Language Translators - Compilers, interpreters
• Application Software
  • MS Office
  • Google Chrome
  • ...
• Utility Software
  • Antivirus
  • Disk Cleaner
  • File compressor / Decompressor
  • ...

OPERATING SySTEM

• Acts as interface between computer and user
• Functions
  • Processor Management - scheduling different applications on the hardware
  • Device Management - Managing I/O devices to interact with user
  • Memory Management - Partitioning and allocating memory in RAM to applications
  • File Management - Managing files in the system - creation, deletion, modification, etc.

COmputer SYSTEM

Application Software

Library Software

Operating System

Hardware