The microprocessor is a multifunction integrated circuit that is, in essence, the Computer. The processor, which is also called the central processing unit (CPU), is made up of several parts. These parts work together to carry out the instructions and actions that translate to a word processing system or a game on your PC.
The primary parts of the CPU, are as follows:
Control Unit (CU) At the risk of being obvious, the control unit controls the functions of the CPU. It is kind of like the manager who coordinates the
activities between the different parts of a factory. It tells the other parts of the CPU how to operate, what data to use, and where to put the results.
Protection Test Unit (PTU) This part of the CPU works with the control unit to monitor whether or not functions are carried out correctly. It is like the quality control department of the CPU. If it detects something is not done properly, it generates an error signal.
Arithmetic and Logic Unit (ALU) The ALU performs all of the calculations and comparative logic functions for the CPU, including all add, subtract, divide, multiply, equal to, greater than, less than, and other arithmetic and logic operations.
Floating Point Unit (FPU) The FPU goes by several other names, including the math coprocessor, the numerical processing unit (NPU), and the numerical data processor (NDP). It handles all floating point operations for the ALU and CU. Floating point operations involve arithmetic on numbers with decimal places and high math operations like trigonometry and logarithms.
Memory Management Unit (MMU) The MMU handles the addressing and cataloging of where data is stored in system memory. Whenever the CPU needs something from memory, it requests it from the MMU. The MMU manages memory segmentation and paging allocations and translates all logical addressing into physical addressing (see Chapter 7 for more information on memory addressing).
Bus Interface Unit (BIU) The BIU supervises the transfer of data over the bus system between the other components of the computer and the CPU. It also serves as the interface point for the CPU and its external bus, as well as handling all data transfers out of the control unit.
The Prefetch Unit This unit preloads the instruction registers of the CPU with instructions from memory whenever the BIU is idle. This allows the CPU to look ahead at future instructions. The prefetch unit does not analyze instructions, so on occasion it may bring in an unnecessary instruction because it assumes that the instructions will be carried out one after the other without branching or jumps.
Decode Unit Many instructions are actually combinations of simpler instructions. The decode unit does just about what its name suggests. It decodes incoming instructions to their simplest form. While the prefetch unit retrieving more instructions, this unit decodes them to get them ready for the control unit.
Registers Built into the CPU are a number of holding areas and buffers that are used to temporarily hold the data, addresses, and instructions being passed around between the CPU's components. These are the registers.
