CPU

Understanding how computers actually work begins with an understanding how the Central Processing Unit (CPU) affects the performance of a computer. The CPU (also “microprocessor or “processor”) is a vital component that is:

• Central — it is the center of computer’s data processing.
• Processor — it processes (moves and calculates) data.
• Unit — it is a chip that contains millions of transistors.

The CPU is the silicon chip (also “silicon wafer”), or processor that makes everything work together. Without the CPU, there would be no Personal Computer (PC). The CPU is the “chip” that performs data manipulation in your computer. A CPU is the brain of the computer. It has millions of switches that control the flow of data; the data is coded into bits by the switches — one bit corresponds to a switch inside the computer that can be “on” or “off”. Computer programs called “software” control the switches.

CPUs continually undergo development and for years have doubled their performance about every 18 months. There is no indication that this trend will stop.

CPUs came into being around 1971, when a then unknown company, Intel, combined multiple transistors to form a central processing unit. It was not until years later that the first personal computers came into being. Personal computers are now built using different makes and models of CPUs and although Intel dominates the market, it is certainly not the only company making them. The first CPUs could only work with whole numbers, but once the CPUs reached the Pentium level a mathematical co-processor, called the Floating-Point Unit (FPU), was added to the CPUs architecture for better math processing.

The CPU is situated on the computer’s motherboard and its work is primarily calculations and data transport. Before it can be processed, the data you enter into the computer is transmitted along a path to the CPU called the system bus. The system bus feeds streams of data (consisting of the data itself and instructions on how to handle the data) to the CPU. You’ve probably heard of “program code.” That’s what the instructions are — program code! Data is what you input via a mouse or a keyboard, i.e., a letter to the telephone company. When you print that letter you actually use “program code” by sending a print instruction to the CPU.

Your computer’s CPU is, in all probability, “8086 compatible” which means that your computer’s various programs communicate with the CPU in a specific family of instructions, which were written for the Intel 8086 processor. This is also known as “the IBM compatible PC.” All IBM compatible processors, no matter how advanced handle the “8086 instruction format.”

Many of the older CPUs had a Complex Instruction Set Computer (CISC), which means the computer could understand many complex instructions. However, Reduced Instruction Set Computer (RISC) is used in most newer CPUs. RISC is exactly what it says - the instructions are brief and the same length (for example 32 bit long) processing much faster than the CISC instructions.

You now understand that a CPU is a data processing gadget that is mounted on a printed circuit board called the motherboard. You know that most of the data processing takes place inside the CPU and that the data is transported via the system bus. However, we have not addressed what determines the speed of the CPU. For example, in the Pentium III, “500 MHz” is the clock frequency. What this means is that a small crystal located on the motherboard constantly ticks to the CPU at a steady number of clock ticks per second and at a “tick” something happens in the CPU. Thus, the more ticks per second (frequency) – the more data that is processed per second.

One problem with high clock frequencies is that when the frequency gets too high it becomes an expensive proposition to design the rest of the computer’s equipment so it can keep pace. Our manufacturing geniuses came up the solution — split the clock frequency in two, this is called clock doubling. Clock doubling uses a high internal clock frequency for the CPU and a lower external clock frequency for the system bus which is where the CPU exchanges data with the RAM and the Input/Output (I/O) units.