In this video we explore the common CPU components and their function. Here we see an abstraction of a computer system. The boundaries of the computer system are represented by the blue shaded box.
We can see the computer accepts inputs from say a keyboard and a mouse and provides output from say a monitor and speakers. The two main internal components of the computer that we're interested in here are the Central Processing Unit and Main Memory. Let's take a look inside the CPU and see what it's made up of.
One important component is the Arithmetic Logic Unit. This is responsible for carrying out calculations and making logical decisions. Another important component is the Control Unit. You can think of this as the command and control center of the CPU. It sends signals to control how data moves around the CPU and coordinates the CPU's operations.
Next is the cache. This is a small amount of very fast memory which is typically located either very close to or actually inside the CPU itself. Its purpose is to provide fast access to frequently used instructions and data.
Information fetched or written to cache is done much quicker than information fetched or written to main memory. The next component is known as the clock. This is an electronic unit that synchronizes related components by generating a pulse at a constant rate. Next, we have the registers.
These are tiny, super fast pieces of onboard memory inside the CPU. Every single one has its own. very specific purpose. At GCSE level you're not required to know the different types of registers or their names, just know that there are many different types. Finally we have the buses.
These are collections of wires through which data and instructions are transmitted from one component to another. Now there are three main types of bus and we look at these in more detail in a later video. There's the address bus which is known as unidirectional, it goes in one direction.
and this carries the addresses which data needs to be written to or read from and these leave the CPU. We then have the data bus, now this is bi-directional and this carries the actual bits, the ones and zeros that represent the data or instructions and these can come from the CPU and head off to memory or they can come from memory and come into the CPU. And finally we have the control bus, another bi-directional bus.
You can think of this as the bus which carries the command and control signals, telling all the various components when they should be receiving read signals or write signals, so it helps to coordinate the CPU. So let's recap what you have learnt. The CPU consists of the following components.
The Arithmetic Logic Unit which performs calculations and logical decisions. The Control Unit that sends signals to control how data moves around the CPU. Cache, which provides a fast access to frequently used data and instructions.
The clock, the electronic unit that synchronises all these related components by generating pulses at a constant rate. Buses, collection of wires through which data and instructions are transmitted from one component to another. And registers, tiny super-fast pieces of onboard memory inside the CPU, each with a very specific purpose.
What comes next is slightly beyond the GCSE specification, so you can stop taking notes. But it's well worth a watch, as it will help bring some concepts together that we look at in other videos, and is excellent bridging information if you intend to go on and study the A-level. So we mentioned in a previous slide that the CPU contains a number of registers, and that these are super-fast pieces of onboard memory, each with a very specific purpose. Now while you're not required to know any of the different registers or their names at GCSE level, there are a few which are handy to know about. Four registers in particular will help to give you a slightly better understanding of how the CPU actually works.
The first is the program counter. This register holds the address of the next instruction to be executed. So no matter what the CPU is currently doing, it can always look inside the program counter to discover where in memory the next instruction is located.
One is called the memory address register. This register holds the address in memory which data or an instruction needs to be read from or written to. In a similar way, there's a register called the memory data register, and this holds either the data or an instruction which has been fetched from memory or the CPU is about to write back to memory.
And finally the accumulator. This is actually a set of general purpose registers which the CPU can utilize for different functions. Temporary values may be stored here before being written to and from memory. Depending on the CPU architecture there may be a different number of registers in the accumulator.