Understanding Processor Terminology

In this section, you learn some basic terms that describe characteristics of different processors - past and present.

Processor speed

Processor speed is the speed at which the processor executes its instructions or commands. This speed was originally measured in millions of hertz, or megahertz (MHz), per second. A hertz is also known as a clock cycle, and a processor can execute code at every clock cycle. Thus, a processor operating at a measly 1 MHz per second can execute one million tasks every second. Processors today now measure their speed in gigahertz (GHz) per second. A gigahertz is a billion clock cycles per second - so the CPU can execute tasks a billion times per second!

Original CPUs had a speed of 4.77 MHz, while systems at the time of this writing are running around 3.0 GHz. Although processor speed is not the only factor affecting performance, in general, the faster the processor, the faster the system.

Data bus

A city bus is responsible for transferring people from one location to another. In the world of computers, a bus is responsible for delivering data from one location on the PC to another. The data bus is the term used to define the pathway between the processor and memory. Because the processor accesses information from memory so often, an entire bus - the data bus - is dedicated to this action. The larger the data bus, the more data can be carried from the CPU to memory in one clock cycle.

Here's an illustration. What would happen if 50 people needed to go from one end of the city to the other, but a city bus had only 25 available seats? The answer is simple. The bus would make two trips. But wouldn't it be more efficient to get a larger bus? If you upgraded the bus to 50 seats, the bus would have to make only one trip to transfer the 50 people from one end of the city to the other, which increases the efficiency of the public transit system.

The data bus works the same way, only it transfers data in the form of bits (a single bit is either a one or a zero). All data processed by the computer is in the form of bits. The data bus has a "full capacity" point at which it cannot handle any more bits of data, just as the bus system in the city has a "full capacity" point (measured in "seats").

If a processor has a 16-bit data bus, it means that it can deliver at most 16 bits during a single clock cycle. If the same processor needs to deliver 32 bits of information, it will have to take two trips, send 16 bits during the first clock cycle and the remaining 16 bits during the next clock cycle. Taking that same 32 bits of information and processing it on a 32-bit processor means that the information will be delivered in one trip - one clock cycle - as opposed to two, which increases the overall efficiency of the system.