Question

Why is the wait-for-memory-function-complete step needed?

Answer 1

Most memory is what we call RAM. This means that you can read and write it. RAM allegedly stands for "random access memory", but this is a complete misnomer because all memory chips support random access. Nevertheless the term RAM has stuck and it really means read/write main memory.

One of the characteristics of RAM is that it loses its value on power-off. But we have many applications where we need memory which doesn't lose its value on power-off. For example, when you turn on your computer, it loads MOST of the operating system in from disk, but some amount of program has to be resident in the computer right from the beginning to control the loading in from disk! Also, computer technology is often used in situations without disks, such as cash registers, vending machines, etc, which in many cases deserve to be called computers, but cannot load software from disk so it has to reside in the computer already at power-on.

Answer 2

The wait-for-memory-function-complete step is needed for the following reasons when reading from or writing to main memory:
1.)To read.
2.)Assert the Read control line.
3.)Wait for the MFC line to be set to 1 by the main memory unit.
4.)Get the date out of the MDR.