THE CENTRAL PROCESSING UNIT (CPU)

The central processing unit (CPU) also known as the processor is the main component of the computer. Its function is to execute instructions sent to it and perform calculations requested by programs. In order to do this, the processor handles data and the activities of the various physical components of the computer, to transfer instructions between the computer hardware and software. Thus the various inputs enter the computer and travels to the central processing unit (CPU). The central processing unit (CPU executes the instructions and delivers the results to the associated outputs.

The main components of the central processing unit (CPU are as follows; the control unit (CU), the arithmetic and logic unit (ALU), the registers, the cache memory and the bus interface unit (BIU).

The control unit monitors and manages the action of the computer and most importantly controls the fetch-execute cycle, by sending control signals to the other components of the central processing unit (CPU. It also sends signals to other components of the computer system, such as the input and output devices. The two main elements of the control unit are the clock and decoder. Pulses are sent out to the other components of the central processing unit (CPU to coordinate their activities and ensure the instructions are carried out and completed. This timing is carried out by a vibrating quartz clock, such that one instruction can be carried out with each pulse of the clock and therefore the higher the clock speed, the faster the central processing unit (CPU will be able to carry the program instructions.

The decoder as the name implies, decodes the program instructions that have been brought from the memory and decides what actions should be taken. It then sends control signals to the other components to carry them out.

The registers are storage locations within the central processing unit (CPU itself. They can be accessed more quickly than the random access memory. The function of the register is to store instructions and data that are currently being used in the fetch- execute cycle.

The cache memory entertains fast memory request by the central processing unit (CPU, by storing frequently accessed data.

While the bus interface unit (BIU) manages data transfer between the central processing unit (CPU and memory.

The central processing unit (CPU processing steps is known as the fetch-execute cycle and the steps are as follows; the first step in the cycle involves fetching instructions from the memory. In other to know how to handle the input and the corresponding instructions for a particular input data it received. It specifically will look for the address of the corresponding instructions and forward the request to the random access memory (RAM). The central processing unit (CPU, and the random access memory (RAM), constantly work together in the processing cycle.

The second step in the cycle is decoding or translating instructions into a form the central processing unit (CPU can understand, which is the machine language or binary.

The third step in the cycle is simply carrying out and executing the given instructions.

While the forth step in the cycle involves storing the results of the execution back to memory for later retrieval if and when requested.

Finally the fifth step of the cycle involves sending an output of some kind, such as to a printer or monitor for printing or display. The fetch –execute cycle happens millions of times per second.

The central processing unit (CPU are classified according to several criteria’s. These criteria’s are based on their architecture, design, functionality and their applications.

The classification according to architecture includes the following; von Neumann architecture, Harvard architecture, reduced instruction set computer (RISC) architecture and complex instruction set computer CISC) architecture.

The von Neumann architecture is the most common processor architecture and it is characterized by separating memory from processing (e.g. Intel core i5, AMD Ryzen 7). The Harvard architecture processors are used widely in embedded systems, this processor is characterized by separating programs and data memory (e.g. microchip pic microcontroller, arm cortex-m). Reduced instruction set computers (RISC) processors are typified by simplified instruction set for execution (e.g. ARM cortex-a53, IBM power 9) While the complex instruction set computers (CISC) processors are typified  by a complex instruction set for improved performance(e.g. Intel core i9, AMD Ryzen thread ripper).

The classification according to design includes the following; monolithic or single chip design (e.g. Intel core i3, AMD Ryzen 3), multi-chip design (e.g. Intel  Xeon w-3175x, AMD EPYC 7742), multi-core design (e.g. Intel core i7, AMD Ryzen 9) and  multi-processor design (e.g. IBM power systems, HP Proliant servers).

These classifications simply means that for monolithic processors are single chip processors, multi-chip processors infers that it is made up of multiple chips on a single substrate, while a multi-core processor consists of multiple processing cores on a single chip, multiple processors is made up of multiple central processing unit (CPU) on a single computer system and finally threaded processors and multi-threaded processor designs are incorporated specifically to enhance and optimize the processors capabilities.

The classification according to functionality includes the following: general purpose central processing unit (CPU) (e.g. Intel core i5, AMD Ryzen 7) which is used for everyday processing and computing. Embedded central processing unit (CPU (e.g. microchip pic 32, Texas instrument msp430), for specialized devices like traffic lights and microwave ovens). Server central processing unit (CPU) (e.g. Intel Xeon, AMD EPYC ), for optimized data centers and servers. Gaming central processing unit (CPU) (e.g. AMD Ryzen 95900x, Intel i9-11900k), for enhance game performance. Mobile central processing unit (CPU (e.g. Apple A15 bionic, QUALCOMM snapdragon 8 gen 2), for everyday mobility needs.

The classification according to applications include the following; desktop c central processing unit (CPU) (e.g. Intel core i5, AMD Ryzen 7) for personal computers. Laptop central processing unit (CPU) (Intel core i3, AMD Ryzen 3), which is optimized for mobile devices. Servers central processing unit (CPU) ( e.g. Intel Xeon, AMD EPYC) for data center and cloud computing. Internet of things central processing unit (CPU)  (e.g. ARM cortex-m,  microchip pic 32), for connected devices.  Artificial intelligence (AI) and machine learning (ML) central processing unit (CPU)(e.g. NVidia Telsa v100, Google tensor processing unit (TPU)).

The trends and projections for now and the future includes; increased core mounts, that is more cores, threads and simultaneous multi-threading. Higher clock speeds of 5 GHz or more. Improved power efficiency, with lower power consumption and better thermal management will be the norm. The trend to more artificial intelligence (AIi integration in processor design will continue.

The future of robots specific processor combining the features of artificial intelligence and machine learning in processor design will become the norm, but whatever it will be; a quantum, Nano scale, DNA or Neurimorphic based processor is left to anyone’s imaginations.

SOURCES.

• Computer organization and design by david A. Patterson.
• Operating system concepts by Abraham Silberschatz.
• CPU manufacturer documentation (intel/AMD).
• Elements of computing systems: building a modern computer from first principles by Noam Nisan and Shimon Schocken.
• The micropressor : a biography by Andrew H. Hedges.