Memory or storage unit is an important unit in digital computer. In Module 3, I have explained the memory module. First, the basic memory module is introduced along with its working principle. Then I moved to advanced features like Cache memory, virtual memory, etc. Some issues of memory management is also included in this module.

In Module 4, I have explained the architectural issues, like different addressing mode, machine instruction and instruction format. The concepts of addressing modes and machine instruction formats are explained in general. For particular machine organization, one may look into Module 11 where the instruction format of 8085 and 8086 are explained in brief.

In Module 5, the design issues of Central processor unit is explained. Both Hardwired-controlled and microprogrammed-controlled control unit design are explained. I have explained the concept in general, without taking any specific architecture or organization.

In Module 6, concept of Input/Output mechanism is explained. The issues related to interrupt and interrupt handling mechanism has been taken care in this module. The concept of DMA is also explained in this module.

In Module 7, the connection of Input/Output devices are explained and the concept of I/O buses are also explained. The organization of Hard Disk, the external storage device is also briefly explained in this module.