Choosing Step 1
Processor
Introduction
The processor or CPU (Central Processing Unit) is the brain of your computer and is arguably the most critical component, as a slow processor will always result in a slow computer.
There are 2 manufacturers of mainstream processors, Intel and AMD. Intel dominates both the mid and high end of the market with its ‘core2‘ processor, while AMD‘s offerings currently only compete in the lower end of the market.
Although the speed of processor you need will vary depending on the way you use your computer (see table left), generally speaking spending 20-30% of your budget on the processor is a good starting point.
There are many factors that determine a processors speed, each of which are explained below, however the most reliable way to compare processor speeds is by looking at ‘benchmarks‘. Benchmarks measure different areas of a processors performance and it‘s unusual to find one processor fastest in all of them. Lots of sites benchmark processors as part of their reviews, searching Google for the processor name + ‘review‘ should yield lots of results.
Tom's Hardware has a very comprehensive set of charts listing most of the processors currently available and their respective benchmark scores.
Examples
Budget PC
For our Budget PC it‘s all about cost, so we will use very low cost AMD processors for our first two examples. Although costing very little these processors still provide decent performance. For the lowest example we must sacrifice dual core, but the slightly more expensive examples will use dual core and so still provide good multitasking potential.
Home PC
Our home PC is expected to run multiple user accounts sumultaniously so we will need a dual core processor to ensure it remains responsive. If we are really splashing out then a low range quad core would be very nice, as with our highest example.
Gaming PC
Although a very fast quad core is the ideal processor for a gaming PC, when it comes to real world performance we actually find that a faster dual core will give better performance than a slower quad in todays games. So our lowest example uses a very popular dual core. Our second example uses the overclockers processor of choice. Although the Q6600 is clocked relatively low at 2.4GHz, it can easily be overclocked to a much higher speed, giving the best of both worlds at a very reasonable price. Finally we have our highest example which can be clocked even higher than the Q6600, giving us the ultimate in gaming performance.
Media Centre PC
Although media centres don‘t tend to be particularly power hungry, we do want out PC to remain responsive even when busy, so a dual core is essential. For our more expensive example we will use a quad core to give us enough power to do almost any tasks simultaniously.
Workstation PC
For our 2D workstation, a fast dual core is more beneficial than a slower quad core, but for 3D the more cores you have for rendering the better, so we‘ll use a very fast quad core that also has potential for overclocking
Explanations
Architecture and Model Number
The architecture of a processor is the way in which its internal circuitry is designed and plays a fundamental role in its performance. Each line of processors (e.g. Intel core2) have the same architecture, which is revised and improved throughout its life. These revisions are usually identifiable in the model name or number.
For example the core2 processor line has model numbers like E8400. The letter refers to whether it is a dual core (E), quad core (Q) or mobile (t) processor. The first number refers to the revision of its architecture and the last 3 numbers are its speed relative to the other processors in this revision. Each revision also has a ‘code name‘; the E8xxx processor line for example is called ‘Wolfdale‘ .
This E8400 is a dual core, core2 architecture, revision 8, with a speed rating of 400 compared to other ‘Wolfdale‘ processors, for example the slower E8200 and the faster E8600.
AMD Phenom processors use a similar naming system, so a Phenom X4 9850 would be the Phenom architecture with 4 cores (X4), revision 9 with a relative speed rating of "850" as opposed to the slower "X4 9750" or faster "X4 9950".
Cores (single, dual, quad)
The inside of an Intel core 2 duo processor. The 'core' is the multi coloured area in the center.
The core is the main part of the processor that does all the work. This core processes information one instruction at a time in a long line. This line of instructions is called a ‘thread‘. These days processors come with multiple of cores, each core able to process one ‘thread‘ at a time.
The advantages of having more cores can be misleading; in most cases it will not make your computer faster at a single task because most programs run using only 1 thread.
Some high end creative programs (3D rendering for example) and newer games can use more than one thread and so benefit greatly from more cores, but for the everyday user the main benefit comes when you are using many programs (and therefore threads) at the same time.
Processors with 2 and 4 cores are referred to as ‘Dual core‘ and ‘Quad core‘ respectively.
Clock Speed (GHz)
The speed at which data is pumped through the processor is called the clock speed. The faster the clock speed the more instructions can be processed in a given time. This can also be misleading as newer processors do more work per clock cycle than older ones. An old Pentium 4 processor running at 3.4GHz is actually slower than a newer core 2 processor running at 2.4GHz.
Use clock speed to compare processors of the same type (e.g. ‘Intel core2‘) rather than comparing different types (eg. Core2 with Phenom).
Cache (MB)
The processor stores instructions that it uses often in its ‘cache‘. This saves it from having to fetch them from memory each time they are needed. Larger Caches therefore mean the processor can work more efficiently when using larger sets of instructions.
Today‘s core2 and Phenom processors show significant performance boosts from larger caches compared to their older counterparts like the Pentium 4.
Front Side Bus(MHz)
The main data route to and from the processor is called the Front Side Bus (FSB). Instructions and information from memory flow along this ‘highway‘ at a speed dictated by the processor.
If the processor is running a task which requires lots of small instructions, like Gaming, a fast FSB can be very beneficial. However, for every day home and office use, faster FSB speeds will not make a noticeable difference to the speed of your computer.
Socket (eg. 775, AM2)
An AMD socket AM2 on a motherboard.
The socket is the part on the motherboard in which the processor sits and therefore both processor and motherboard sockets must match. You may see the same model of processor that is available for 2 different socket types. In this case it is usually best to get the newest socket type, as this will provide you with more opportunities to upgrade in the future.
‘OEM‘ or ‘Retail‘
When shopping for processors online, you will see either ‘OEM‘ or ‘Retail‘ on the end of the processor name. OEM stands for ‘Original Equipment Manufacturer‘ and were originally created for companies building many computers. They do not come with in a box with a heat sink, instead all you get is a processor in a plastic wrapper.
‘Retail‘ processors are aimed at people building a single system and include the manufacturers heat sink all packaged in a colourful box with installation instructions. Unless you intend to buy a special heat sink separately (e.g. for overclocking), we would recommend buying a retail processor.
Related Links
Tom‘s Hardware Desktop Processor Performance ChartComplete set of processor benchmarks. Charts for various benchmarks with the ability to add processors both past and present.
Trusted Reviews: CPUsGood source for non-technical reviews and news of processors, including a few benchmarks.
AnandTech: CPUsGood source for technical reviews and news of Processors, including extensive benchmarks.
Legit Reviews: ProcessorsHigh quality reviews of Processors and other components, as well as news and articles.
CPU history and technical explanation of operation, design and implementation.
