Parts of CPU and their role 

A CPU is a complex IC chip containing millions of transistors. As mentioned earlier, a CPU consists of three main identifiable parts: the control unit (CU), the arithmetic logic unit (ALU), and a set of registers. The CPU chip is connected to the other components of the computer via the system bus (wires printed on the motherboard), which consists of three sets of wires constituting the control bus, the data bus, and the address bus. 

The CPU has a set of registers that are used to temporarily store specific data. A computer's memory hierarchy consists of registers located above the cache and main memory. Registers in a CPU serve two purposes:- 

1. User-visible registers:- Used to store temporary data items and other information that is accessible to the user and useful to the machine or assembly language programmer. 

2. Control and status registers:- Used by the control unit to control and coordinate the operation of the processor.

Parts of CPU and their role 

The control unit of a processor is the unit that controls and coordinates the execution of the processor's instructions. It is responsible for defining and controlling the teaching cycle. In short, it makes things happen in the application. It provides control signals outside the processor to exchange data with memory and I/O modules. It provides control signals internal to the processor to transfer data between registers, instruct the ALU to perform a specific function, and regulate other internal functions. It generates a timing signal and starts the instruction execution fetch cycle. When an instruction is received, it creates a sequence of micro-operations that must be executed to execute the instruction. The CU also generates timing signals to execute a set of micro-operations. There are three different ways in which the CU can perform these micro-operations: via hardware logic, by reading a programmable array table (PLA), or by reading a programmable read-only memory (PROM).

In hardwired control, the mapping between machine instructions and the resulting microtasks is permanently hardwired into the processor. This is a relatively fast method, although it cannot be changed. A sequence of microfunctions created to execute an instruction in a PLA control is stored as a PLA table. In microprogram control, the logic of the control unit is specified by the firmware. A firmware specifies microfunctions. A firmware controller has a control memory (PROM chip) that stores a sequence of microoperations. Typically, processors with small instruction sets (such as RISC processors) have hardwired control logic, while microprocessor control is used in processors with large instruction sets.

The Arithmetic and Logical Unit is that portion of the CPU that really performs number juggling and coherent operations on information. The CU, CPU registers and memory offer assistance in bringing the data into the ALU and at that point taking the comes about back. Figure underneath presents the ALU inputs and yields:-

ALU receives data in registers and the results are also stored in registers. Accumulator is a frequently used register during ALU operations. ALU contains several registers such as flag and status registers which represent information about the operation and its result. Logic is implemented in ALU to perform operations like addition, multiplication, division, shift, complement etc. The operations are performed on the displayed numbers, both integer and floating point.

There are two recognizable trends in modern processors today which are improving their performance to a very high level. These are the use of on-chip cache memory and multiple processor cores on a single IC chip. Cache memory is a fast semiconductor memory used to temporarily store instructions and data that are frequently referenced by the processor. By making frequently referenced instructions and data available to the processor, the wait cycles introduced due to memory references are reduced and thus the processor performance is greatly improved. Another modern technology is to have multiple processor cores on the same IC chip, which attempt to execute instructions in parallel, thereby greatly improving the processor performance.