The fastest bus of all is the connection between the processor and its primary cache, and this is kept within the CPU chip. The next level down is the system bus, which links the processor with memory, both the small amount of Static RAM (SRAM) secondary cache and the far larger main banks of Dynamic RAM (DRAM). The system bus is 64 bits wide and, for Intel-based designs, was capped at 66MHz until early 1998, when a new Pentium II chipset raised this to 100MHz. The CPU doesn't communicate directly with the memory, but through the intermediary of the System Controller chip, which manages the host bus and bridges between it and, in modern PCs, the PCI bus.

Processors using a Dual Independent Bus (DIB) architecture - present on Intel designs from the Pentium II onwards - have replaced the single system bus with two independent buses, one for accessing main memory and the other for accessing the Level 2 cache. These are referred to as the frontside bus and the backside bus respectively.

The key concept was of an open architecture based on a simple expansion bus that facilitated the easy connection of additional components and devices. Nearly two decades after its introduction, it was still possible to fit original add-on cards into a modern PC - a tribute to the staying power of the design. Whilst there have been a number of dead ends along the way, the evolution of standard expansion bus designs has been remarkably robust over the years.

Although there have always been other chipset manufacturers - such as SIS, VIA and Opti - for many years Intel's "Triton" chipsets were by far the most popular. Indeed, the introduction of the Intel Triton chipset caused something of a revolution in the motherboard market, with just about every manufacturer using it in preference to anything else. Much of this was down to the ability of the Triton to get the best out of both the Pentium processor and the PCI bus, together with its built-in master EIDE support, enhanced ISA bridge and ability to handle new memory technologies like EDO and SDRAM. However, the new PCI chipsets" potential performance improvements will only be realised when used in conjunction with BIOSes capable of taking full advantage of the new technologies on offer.

During the late 1990s things became far more competitive, with Acer Laboratories (ALI), SIS and VIA Technologies all developing chipsets designed to operate with Intel, AMD and Cyrix processors. 1998 was a particularly important year in chipset development, with what had become an unacceptable bottleneck - the PC's 66MHz system bus - to finally being overcome. Interestingly, it was not Intel but rival chipmakers that made the first move, pushing Socket 7 chipsets to 100MHz. Intel responded with its 440BX, one of many chipsets to use the ubiquitous Northbridge/Southbridge architecture. It was not long before Intel's hold on the chipset market loosened further still, and again, the company had no-one but itself to blame. In 1999, its single-minded commitment to Direct Rambus DRAM (DRDRAM) left it in the embarrassing position of not having a chipset that supported the 133MHz system bus speed its latest range of processors were capable of. This was another situation its rivals were able to exploit, and in so doing gain market share.

Memory

The system memory is the place where the computer holds current programs and data that are in use, and, because of the demands made by increasingly powerful software, system memory requirements have been accelerating at an alarming pace over the last few years. The result is that modern computers have significantly more memory than the first PCs of the early 1980s, and this has had an effect on development of the PC's architecture. Storing and retrieving data from a large block of memory is more time-consuming than from a small block. With a large amount of memory, the difference in time between a register access and a memory access is very great, and this has resulted in extra layers of "cache" in the storage hierarchy.

When it comes to access speed, processors are currently outstripping memory chips by an ever-increasing margin. This means that processors are increasingly having to wait for data going in and out of main memory. One solution is to use "cache memory" between the main memory and the processor, and use clever electronics to ensure that the data the processor needs next is already in cache.

Hard Disks

When the power to a PC is switched off, the contents of memory are lost. It is the PC's hard disk that serves as a non-volatile, bulk storage medium and as the repository for a user's documents, files and applications. It's astonishing to recall that back in 1954, when IBM first invented the hard disk, capacity was a mere 5MB stored across fifty 24in platters. 25 years later Seagate Technology introduced the first hard disk drive for personal computers, boasting a capacity of up to 40MB and data transfer rate of 625 KBps using the MFM encoding method. A later version of the company's ST506 interface increased both capacity and speed and switched to the RLL encoding method. It's equally hard to believe that as recently as the late 1980s 100MB of hard disk space was considered generous. Today, this would be totally inadequate, hardly enough to install the operating system alone, let alone a huge application such as Microsoft Office.

The PC's upgradeability has led software companies to believe that it doesn't matter how large their applications are. As a result, the average size of the hard disk rose from 100MB to 1.2GB in just a few years and by the start of the new millennium a typical desktop hard drive stored 18GB across three 3.5in platters. Thankfully, as capacity has gone up prices have come down, improved areal density levels being the dominant reason for the reduction in price per megabyte.

It's not just the size of hard disks that has increased. The performance of fixed disk media has also evolved considerably. When the Intel Triton chipset arrived, EIDE PIO mode 4 was born and hard disk performance soared to new heights, allowing users to experience high-performance and high-capacity data storage without having to pay a premium for a SCSI-based system.

CDR-RW

Normal music CDs and CD-ROMs are made from pre-pressed discs and encased in plastic. The actual data is stored through pits, or tiny indentations, on the silver surface of the internal disc. To read the disc, the drive shines a laser onto the CD-ROM's surface, and by interpreting the way in which the laser light is reflected from the disc it can tell whether the area under the laser is indented or not.

Thanks to sophisticated laser focusing and error detection routines, this process is pretty much ideal. However, there's no way the laser can change the indentations of the silver disc, which in turn means there's no way of writing new data to the disc once its been created. Thus, the technological developments to enable CD-ROMs to be written or rewritten to have necessitated changes to the disc media as well as to the read/write mechanisms in the associated CD-R and CD-RW drives.

At the start of 1997 it appeared likely that CD-R and CD-RW drives would be superseded by DVD technology almost before they had got off the ground. In the event, during that year DVD Forum members turned on each other triggering a DVD standards war and delaying product shipment. Consequently, the writable and rewritable CD formats were given a new lease of life.

For professional users, developers, small businesses, presenters, multimedia designers and home recording artists the recordable CD formats offer a range of powerful storage applications. Their big advantage over alternative removable storage technologies such as MO, LIMDOW and PD is that of CD media compatibility; CD-R and CD-RW drives can read nearly all the existing flavours of CD-ROMs and discs made by CD-R and CD-RW devices can be read on both (MultiRead-capable) CD-ROM drives and current and all future generations of DVD-ROM drive. A further advantage, itself a consequence of their wide compatibility, is the low cost of media; CD-RW media is cheap and CD-R media even cheaper. Their principal disadvantage is that there are limitations to their rewriteability; CD-R, of course, isn't rewritable at all and until recently CD-RW discs had to be reformatted to recover the space taken by "deleted" files when a disc becomes full, unlike the competing technologies which all offer true drag-and-drop functionality with no such limitation. Even now, however, CD-RW rewriteability is less than perfect, resulting in a reduction of a CD-RW disc's storage capacity

Graphics Cards

Video or graphics circuitry, usually fitted to a card but sometimes found on the motherboard itself, is responsible for creating the picture displayed by a monitor. On early text-based PCs this was a fairly mundane task. However, the advent of graphical operating systems dramatically increased the amount of information needing to be displayed to levels where it was impractical for it to be handled by the main processor. The solution was to off-load the handling of all screen activity to a more intelligent generation of graphics card.

As the importance of multimedia and then 3D graphics has increased, the role of the graphics card has become ever more important and it has evolved into a highly efficient processing engine which can really be viewed as a highly specialised co-processor. By the late 1990s the rate of development in the graphics chip arena had reached levels unsurpassed in any other area of PC technology, with the major manufacturers such as 3dfx, ATI, Matrox, nVidia and S3 working to a barely believable six-month product life cycle! One of the consequences of this has been the consolidation of major chip vendors and graphics card manufacturers.

Chip maker 3dfx started the trend in 1998 with the its acquisition of board manufacturer STB systems. This gave 3dfx a more direct route to market with retail product and the ability to manufacture and distribute boards that bearing its own branding. Rival S3 followed suit in the summer of 1999 by buying Diamond Mulitmedia, thereby acquiring its graphics and sound card, modem and MP3 technologies. A matter of weeks later, 16-year veteran Number Nine announced its abandonment of the chip development side of its business in favour of board manufacturing.

The consequence of all this manoeuvring was to leave nVidia as the last of the major graphics chip vendors without its own manufacturing facility - and the inevitable speculation of a tie-up with close partner, Creative Labs. Whilst there'd been no developments on this front by mid-2000, nVidia's position had been significantly strengthened by S3's sale of its graphics business to VIA Technologies in April of that year. The move - which S3 portrayed as an important step in the transformation of the company from a graphics focused semiconductor supplier to a more broadly based Internet appliance company - left nVidia as sole remaining big player in the graphics chip business. In the event, it was not long before S3's move would be seen as a recognition of the inevitable.

In an earnings announcement at the end of 2000, 3dfx announced the transfer of all patents, patents pending, the Voodoo brandname and major assets to bitter rivals nVidia and recommended the dissolution of the company. In hindsight, it could be argued that 3dfx's acquisition of STB in 1998 had simply hastened the company's demise since it was at this point that many of its hitherto board manufacturer partners switched their allegiance to nVidia. At the same time nVidia sought to bring some stability to the graphics arena by making a commitment about future product cycles. They promised to release a new chip out every autumn, and a tweaked and optimised version of that chip each following spring. To date they've delivered on their promise - and deservedly retained their position of dominance!

Inkjet Printers

Although inkjets were available in the 1980s, it was only in the 1990s that prices dropped enough to bring the technology to the high street. Canon claims to have invented what it terms "bubble jet" technology in 1977, when a researcher accidentally touched an ink-filled syringe with a hot soldering iron. The heat forced a drop of ink out of the needle and so began the development of a new printing method.

Inkjet printers have made rapid technological advances in recent years. The three-colour printer has been around for several years now and has succeeded in making colour inkjet printing an affordable option; but as the superior four-colour model became cheaper to produce, the swappable cartridge model was gradually phased out.

Traditionally, inkjets have had one massive attraction over laser printers; their ability to produce colour, and that is what makes them so popular with home users. Since the late 1990s, when the price of colour laser printers began to reach levels which made them viable for home users, this advantage has been less definitive. However, in that time the development of inkjets capable of photographic-quality output has done much to help them retain their advantage in the realm of colour.

The down side is that although inkjets are generally cheaper to buy than lasers, they are more expensive to maintain. Cartridges need to be changed more frequently and the special coated paper required to produce high-quality output is very expensive. When it comes to comparing the cost per page, inkjets work out about ten times more expensive than laser printers.

Since the invention of the inkjet, colour printing has become immensely popular. Research in inkjet technology is making continual advances, with each new product on the market showing improvements in performance, usability, and output quality. As the process of refinement continues, so the price of an inkjet printers continue to fall.

Scanners

Digital imaging has come of age. Equipment that was once reserved for the wealthiest bureaux is now commonplace on the desktop. The powerful PCs required to manipulate digital images are now considered entry level, so it comes as no surprise to learn that scanners, the devices used to get images into a PC, are one of the fastest growing markets today.

At its most basic level, a scanner is just another input device, much like a keyboard or mouse, except that it takes its input in graphical form. These images could be photographs for retouching, correction or use in DTP. They could be hand-drawn logos required for document letterheads. They could even be pages of text which suitable software could read and save as an editable text file.

The list of scanner applications is almost endless, and has resulted in products evolving to meet specialist requirements:

* high-end drum scanners, capable of scanning both reflective art and transparencies, from 35mm slides to 16-foot x 20in material at high (10,000dpi+) resolutions
* compact document scanners, designed exclusively for OCR and document management
* dedicated photo scanners, which work by moving a photo over a stationary light source
* slide/transparency scanners, which work by passing light through an image rather than reflecting light off it
* handheld scanners, for the budget end of the market or for those with little desk space.

However, flatbed scanners are the most versatile and popular format. These are capable of capturing colour pictures, documents, pages from books and magazines, and, with the right attachments, even scan transparent photographic film.