The data bus is used to transfer the data b/w CPU and the I/O device or memory. The data can be taken into the processor or supplied by the processor to the peripheral devices by the same bus. The data bus of the microprocessor system is made bidirectional to economize the number pins in the microprocessor IC.
As discussed earlier the data bus latch its contents in address bus's lower byte.
The width of the data bus is equal to the number of the bits the microprocessor can process at a time. The width of data bus of 8 bit microprocessor being equal to 8 bits(1byte). It can take 1 byte of data in a memory location or peripheral device.