In PIO, the CPU handles all data transfers between memory and a device.

Example:
- Device → Memory: CPU reads data from the device into a register, then copies it to memory.
- Memory → Device: CPU reads data from memory into a register, then writes it to the device.

Why it was used?

In early PCs, PIO was common because:

• Devices were simpler and cheaper (no need for complex transaction logic).
• The CPU was fast enough to manage transfers itself.
• The CPU often had no other tasks (single-tasking systems).

Drawbacks of PIO

Two bus cycles per transfer → inefficient.

• One to read into the CPU register.
• One to write from the CPU register.

CPU is tied up with transfer work, instead of running applications.