Now we discuss the design of memory subsystem using memory chips. Consider a memory chips of capacity 16K x 8. The requirement is to design a memory subsystem of capacity 64K x 16. Each memory chip has got eight lines for data bus, but the data bus size of memory subsytem is 16 bits.
The total requiremet is for 64K memory location, so four such units are required to get the 64K memory location. For 64K memory location, the size of address bus is 16. On the other hand, for 16K memory location, size of address bus is 14 bits.
Each chip has a control input line called Chip Select (CS). A chip can be enabled to accept data input or to place the data on the output bus by setting its Chip Select input to 1. The address bus for the 64K memory is 16 bits wide. The high order two bits of the address are decoded to obtain the four chip select control signals. The remaining 14 address bits are connected to the address lines of all the chips. They are used to access a specific location inside each chip of the selected row. The inputs of all chips are tied together to provide a common control.