DMA & System Architectures (Amiga→PC→SoC)

DMA & System Architectures (Amiga→PC→SoC)

This page explains how Direct Memory Access (DMA) improves system performance and shows examples of different hardware architectures.

Direct Memory Access (DMA)

In a system without DMA, the CPU must handle every data transfer:

1. Read data from peripheral into a register.
2. Write the data from the register into memory.

This creates overhead and slows down performance.

With DMA, a peripheral can transfer data directly to or from memory:

• The peripheral temporarily takes control of the bus.
• Data moves in a single step without involving the CPU.
• Special control signals decide who has control of the bus.

DMA in practice

Example: a network card receives a packet.

• Without DMA: CPU copies the packet from the card into RAM.
• With DMA: the card writes the packet directly into RAM (or cache), saving CPU time.

Hardware architectures

Amiga 500 mainboard

A 1980s home computer with clearly separated components: CPU, RAM, ROM, graphics, audio, I/O ports, and DMA controller.

PC motherboard

Modern boards integrate CPUs, chipsets, memory slots, and a variety of controllers connected via buses such as PCI Express.

System on a Chip (SoC)

Today, even inexpensive chips integrate:

• Multiple CPU cores,
• Memory,
• Peripherals,
• Programmable I/O.

Microcontrollers may cost only a few cents while providing a complete computer on a single chip.