Bus Interface Unit (BIU)

Microprocessors are now extensively used in many applications. A microprocessor consists of a central processing unit (CPU), memory, input devices and output devices. For the interconnection of these components, buses are used. A bus is a group of parallel lines which carries digital information between digital devices in a system. There exist three varieties here – address bus, data bus and control bus. Control bus is composed of various control lines. Data bus is used for sending information between microprocessor and memory or input/output devices (bidirectional). Address bus is used for sending information from microprocessor to memory or input/output devices (unidirectional).  Memory can be either RAM or ROM. Different input/output devices used here are keyboard, mouse, modem, ADC, DAC, monitor, printer etc. Bus interface unit (BIU) handles all bus operations. BIU generally contains first in first out registers of size 6 bytes in length called queue. BIU performs prefetching of instructions from memory and then stores these instructions in the queue. This process is termed as pipelining which increases the speed of microprocessors.