CPU Organization

In previous sections, we discussed computer organization at the microarchitectural level, processor organization (in terms of datapath, control, and register file), as well as logic circuits including clocking methodologies and sequential circuits such as latches.

In Figure 4.1, the typical organization of a modern von Neumann processor is illustrated. Note that the CPU, memory subsystem, and I/O subsystem are connected by address, data, and control buses. The fact that these are parallel buses is denoted by the slash through each line that signifies a bus.

• Processor (CPU) is the active part of the computer, which does all the work of data manipulation and decision making.
• Datapath is the hardware that performs all the required operations, for example, ALU, registers, and internal buses.
• Control is the hardware that tells the datapath what to do, in terms of switching, operation selection, data movement between ALU components, etc.

The processor represented by the shaded block in Figure 4.1 is organized as shown in Figure 4.2. Observe that the ALU performs I/O on data stored in the register file, while the Control Unit sends (receives) control signals (resp. data) in conjunction with the register file.