How main memory is useful in computer system ?Explain the memory address map of RAM and ROM.

Main memory is useful in computer system :

1.The main memory occupies a central position in a computer system.

2.It is able to communicate directly with the CPU and with auxiliary memory devices through an I/O processor.

3.It is relatively large and fast.
Memory address map of RAM and ROM :

1.Memory address map is a pictorial representation of assigned address space for each chip in the system.

2.To demonstrate with a particular example, assume that a computer system needs 512 bytes of RAM and 512 bytes of ROM.

3.The RAM and ROM chips to be used are specified in image The memory address map for this configuration is shown in Table 1.

4.The component column specifies whether a RAM or a ROM chip is used. The hexadecimal address column assigns a range of hexadecimal equivalent addresses for each chip. The address bus lines are listed in the third column.

5.The selection between RAM and ROM is achieved through bus line 10. The RAMs are selected when the bit in this line is 0, and the ROM when the bit is 1.

6.The × under the address bus lines designate those lines that must be connected to the address inputs in each chip.

7.The RAM chips have 128 bytes and need seven address lines.

8.The ROM chip has 512 bytes and need 9 address lines.

9.It is now necessary to distinguish between four RAM chips by assigning to each a different address.