Are Computers same for 40 years — Von Newman Architecture

Have you ever wondered how exactly computer does all the tasks from browsing, playing games, videos, editing documents, etc… By Computers I mean every thing from mobile phones, laptops to Dedicated server class machines and even world fastest super computers. All most all of them work on same basic design done by Von Newmann popularly known as ‘Von Newmann Architecture’. Let us discuss about it on a high level in this post.

types of computers

Basic characteristics of any computer:

  • Program is stored in memory during execution
  • Program instructions are executed sequentially till a halt instruction is executed
Architecture of computers

Memory sub-system:

Typically memory sub-system is accessed via
- Fetch (address) and
-Store (address, value) calls
These calls are implemented with the help of interfaces of the system
-Memory Address Register (MAR)
-Memory Data Register (MDR)
-Fetch/Store signal

ALU sub-system:

  • mathematical operations (+, -, x, /, …)
  • logic operations (=, <, >, and, or, not, …)

Typically they have hard-wired circuits for arithmetic/logic operations, Registers (to store intermediate results) and bus that connects them.

Control Unit sub-system:

  • In Fetch cycle — next instruction to be executed is loaded from memory.
  • In Decode cycle — it decodes the fetched instruction (recognize what need to be done)
  • In Execute cycle — it Executes the instruction by issuing the appropriate signals to the ALU, memory, and I/O subsystems.

It repeats the same steps till it executes HALT instruction. The following 2 registers plays a major role in control unit sub-system:

  • Instruction Register(IR) contains current instruction in execution
  • Program Counter(PC) contains address of next instruction to be executed

Input/Output sub-system:

  • Communicate and interact with users like Display Screen, keyboard, Mouse…
  • Store information/data like Hard-disks, CD/DVD, tapes…

For more details