Understanding Computer Architecture

The Basics – You Must Know

What is a computer?

A computer is an electronic machine or a programmable device that can store, retrieve and process data.

Computer Architecture

Computer Architecture – The von Neumann Architecture

The Components of Architecture

• Central Processing Unit (CPU):

The CPU is the brain of the computer, consisting of:

Arithmetic Logic Unit (ALU): Performs arithmetic and logical operations.

Control Unit (CU): Directs the flow of data and instructions.

Registers: Small, high-speed storage for temporary data.

Example: In an Intel i7 processor, the ALU handles integer and floating-point calculations, while the CU manages instruction sequencing.

• Memory Organization:

Memory stores data and instructions for processing. It is organized in a hierarchy:

Primary Memory: RAM (volatile) and cache (fast access).

Secondary Memory: Hard drives, SSDs (non-volatile).

Virtual Memory: Extends RAM using disk space.

Example: A system with 16GB RAM and 512GB SSD uses paging to manage virtual memory.

• Input/Output (I/O) Organization:

Handles communication between the CPU and external devices.

I/O Interfaces: Memory-mapped or isolated I/O.

Interrupts & DMA: Efficient data transfer without CPU intervention.

Example: A keyboard sends interrupts to the CPU, while a disk uses DMA for bulk data transfer.

• Bus Systems:

Buses are communication pathways for data, addresses, and control signals.

Data Bus: Transfers actual data.

Address Bus: Specifies memory locations.

Control Bus: Manages read/write operations.

Example: PCIe bus connects GPUs to the CPU for high-speed data exchange.

• Pipelining & Parallelism:

Improves performance by overlapping instruction execution stages.

Instruction Level Parallelism (ILP) and Branch Prediction reduce delays.

Example: Modern CPUs like ARM Cortex-A use 5-stage pipelines to execute multiple instructions simultaneously.

• Instruction Set Architecture (ISA):

Defines the CPU’s commands, addressing modes, and data formats.

Reduced Instruction Set Computer (RISC): Simple, fast instructions (e.g., ARM).

Complex Instruction Set Computer (CISC): Complex instructions (e.g., x86).

Example: ARM ISA powers most smartphones for energy efficiency.