BIU(Bus Interface Unit) is responsible for fetching the instructions into the Queue.
The Bus Interface Unit (BIU) generates the 20-bit physical memory address and provides the interface with external memory (ROM/RAM).8086 has a single memory interface. To speed up the execution, 6-bytes of instruction are fetched in advance and kept in a 6-byte Instruction Queue while other instructions are being executed in the Execution Unit (EU). Hence after the execution of an instruction, the next instruction is directly fetched from the instruction queue without having to wait for the external memory to send the instruction. This is called pipe-lining and is helpful for speeding up the overall execution process.
Refer the link for more details:
https://nptel.ac.in/courses/Webcourse-contents/IIT-KANPUR/microcontrollers/micro/ui/Course_home4_29.htm
