Chips off the old block

In our mission to crack the baffling code used in computer adverts, we turn the spotlight onto one obscure yet critical element of your PC's configuration - the chipset, or the group of chips soldered onto a computer's motherboard.

In some adverts, there's no mention of the chipset at all, while in others you're presented with a bamboozling equation of mystical numbers and digits. And then there's cache, in its many puzzling flavours. Just what on earth are we to make of all this jargon? While you're not going to buy a PC based on the chipset it uses, you'll still want to be armed with enough knowledge to know what you're being sold.

Here we're covering the system chipset - the microchips that control the flow of data from one part of a computer to another. Specifically, the system chipset sits between the processor, the memory modules (RAM) and all the various bits and bobs that make up a system.

Chips off the old block
Chipsets have evolved quite dramatically over time. As processors grow ever faster, chipsets have had to find new ways to efficiently channel all this raw power into and through the system. While a chipset cannot by itself improve processor performance, an inefficient design could certainly slow it down. So perhaps it's no surprise that Intel, maker of popular processors from the 486 model and earlier through to today's Pentium III range, has also long led the way in chipset design and manufacturing.

Not all chipsets are made by Intel, but they do dominate so we'll cover them first. Now for the techie bit. Generally, an Intel chipset consists of two microchips, known as northbridge and southbridge. The former controls the data flow between the heavy-duty parts of a system such as the processor, graphics card and memory, while the latter handles the lighter duties of the hard disk, keyboard, mouse and peripheral devices. Jointly, these chips provide a network through which any part of a PC can communicate with any other part.

It's a bit like a complex traffic system designed to link different areas together at high speeds. Think of Spaghetti Junction - then imagine that it works. If it wasn't for a humble system chipset directing the frenzied flow of electrons, your PC's processor couldn't count so much as a bean and its memory would have chronic amnesia.

Intel's 440LX chipset was long the standard model for use in PCs using the Pentium II processor and with the related, but slower, Celeron processor. However, its system bus speed wasn't the quickest so the LX was eventually replaced by the faster 440BX chipset. This is the chipset quoted in our example and is currently the best bet for mid to top-range Pentium III computers. There is a slightly cheaper version of the 440BX known as the ZX but it can only work with a maximum of 256Mb of memory.

Newer than the 440BX are Intel's 810 and 810e chipsets. These models integrate sound and graphical functions within the chipset, thus doing away with the need for either separate expansion cards or audio and graphics chipsets on the motherboard. These are used in budget systems to keep the price low, but when it comes to games playing you may be disappointed with their performance.

It pays to make sure you're absolutely clear what is powering the graphics when buying a PC. Get the salesperson to spell it out for you - don't just assume that when it says it's the same as AGP, it is AGP. Something that's the same as AGP could in fact be a chipset that's doubling as a graphics chip, and that may not suit your needs.

Thanks for the memory
Beyond the 810 family we find the 820 and 840. Such chipsets are designed to complement a new, faster and more costly type of memory (known as RD RAM) and so are generally reserved for the ultimate in desktop machines and servers using multiple processors.

The appearance of the AMD Athlon processor towards the end of last year somewhat shifted the goalposts. The Athlon uses an entirely different species of chipset (called the AMD-750) to do its business and - naturally enough - only AMD makes it. From the shopper's point of view, this rather helps, as you simply don't have any chipset options to worry about when buying an Athlon-powered PC. This is just fine, as the AMD-750 is the perfect partner for the all-conquering Athlon.

Several manufacturers are in on the chipset act these days, notably VIA, ALi and SiS. It's not possible for us to list all of the possible processor/chipset permutations here. We would simply make the following observation: if major PC manufacturers such as Dell and Compaq are happy using VIA chipsets in partnership with state-of-the-art Intel processors, it's a pretty safe bet that they know what they're doing.

Our advice is straightforward: if you're buying a new Pentium III computer today, expect and demand an Intel 440BX chipset with 512Kb cache (or, if your system comes with RD RAM, one of the latest 820 models). For a Celeron machine, an LX chipset is perfectly adequate and, in our view, a better bet than the 810 family because it's easier to upgrade the sound and graphics functions later. That said, an 810 chipset is okay if tinkering isn't your thing and you've no interest in playing games or graphics-intensive projects.

If the chipset is either not specifically identified or made by a company other than Intel, we'd suggest asking your supplier for details - and, if you're not convinced that their choice is sound, consider looking elsewhere. But don't forget the meaty Athlon/AMD-750 combo. Intel Inside is all very well but these days it's not compulsory.

Time to cache up
When you use your computer - to write a letter in a word processor, for example, or edit a spreadsheet - the software application itself and much of the raw data that it needs are held in the memory (RAM). This is like a temporary working space. However, because today's processors are powerful and memory is relatively slow, a bottleneck develops whenever data is sent to and retrieved from the memory. For this reason, modern computers use a buffering system known as caching, whereby small blocks of very fast memory are used to feed the processor the bits of information it needs from one instant to another.

There are two forms of cache. Primary, or level one, cache is an area of memory that's physically attached to the processor chip which operates at the same speed as the processor. However, because it's expensive to manufacture, primary cache is typically only between 8Kb and 64Kb in size and thus constantly over-stretched. And so there's also secondary, or level two cache. Held in one of the distinct microchips that makes up a chipset, this sits between the memory and the processor and is generally found in chunks of 256Kb or 512Kb. The more cache you can get hold of, the better. The 512Kb of secondary cache quoted in our example specification is ample.

Bus speeds - for data to pass from one area of a computer to another - from the hard disk into memory, for example - it has to go through a gateway known as a bus. It sounds complicated but a bus is just a set of thin wires through which data flows. Some buses are relatively slow, such as outmoded ISA slots, while others, such as USB ports, can handle much more data much more quickly. The chipset controls all of the bus routes and makes sure that everything is running smoothly. But it also has a bus all of its own, known as the system bus, through which it communicates with both the computer at large and its own various components. System bus speed is measured in megahertz and is generally 66Mhz (such as Intel's 440LX chipset) or 100Mhz (like the 440BX in our example). Even higher bus speeds of 133Mhz are now also around.

Meanwhile, while no one was looking, AMD decided to throw away the system bus blueprint and introduced something called point-to-point channelling, as seen(through a microscope) in its Athlon processor. The upshot is that data positively rockets through the AMD-750 chipset at a theoretical top speed of 200Mhz, which is rather impressive.