Programmed I/O: In program-controlled I/O, the processor program controls the complete data transfer. So only when an I/O transfer instruction is executed, the transfer could take place. It is required to check that device is ready/not for the data transfer in most cases.  Usually, the transfer is to & from a CPU register & peripheral. Here, CPU constantly monitors the peripheral. Here, until the I/O unit indicates that it is ready for transfer, the CPU wait & stays in a loop. It is time-consuming as it keeps the CPU busy needlessly.

✅ Memory Unit Communication with CPU:

The memory unit which directly communicates with the CPU is known as:

✅ Primary Memory:

Primary memory, also called Main Memory, includes components like RAM (Random Access Memory) and Cache Memory.

✅ Why Primary Memory?

Primary memory is directly accessible by the CPU, allowing it to fetch data and instructions quickly for processing.

✅ Final Answer:

The memory unit that directly communicates with the CPU is: Primary Memory or Main Memory

Time for Fetch & Execute

Definition:
The time required to fetch and execute one machine instruction is called a Machine Cycle / CPU Cycle.

Includes:

• Instruction fetch
• Instruction decode
• Operand fetch (if any)
• Execution
• Result store (if any)

✅ Final Answer: Machine Cycle / CPU Cycle.