The most important shift of recent years has been the development of user-friendly 'point-and-click' graphical interfaces such as Microsoft's Windows, which is rapidly becoming the standard way to operate a PC-compatible computer, leaving the opaque Dos text-based system to run unseen underneath.
Now, two of the industry's arch-rivals, Apple and IBM, are collaborating to bring about what they hope will be the next paradigm shift. Along with the microprocessor manufacturer, Motorola, the two companies have developed a new range of microprocessors they call PowerPC. According to the alliance, PowerPC is different not just in the impressive speed claimed for it, but more importantly in that it can run different operating systems.
Programs such as word processors and spreadsheets have to be written for use with a specific operating system - the software that controls the basic functions of the computer - but most operating systems are designed to run on one specific type of computer processor.
Microsoft's Dos and Windows operating systems will only run on processor chips designed by the giant Intel, while Apple's System 7 was designed for Motorola's 68000 range of processors.
This has given Intel and Microsoft immense control over the computer industry. If you want to use a word processor such as Lotus's Ami Pro that was written for the Windows, then you have to buy an Intel-based PC. It will not run on an Apple Macintosh or a workstation like a Sun, running the Unix operating system. More than 80 per cent of the personal computers in use worldwide run on Intel processors and Microsoft operating systems.
PowerPC's ability to run a range of operating systems means users no longer have to buy a specific brand of computer to use their favourite programs. 'PowerPC will be a really independent platform,' according to Amelia Knight of Apple UK. Other companies that plan to make their operating systems available for the PowerPC include the Unix market leader, Sun Microsystems, and Microsoft with its Windows NT.
In a year you may be able to buy an IBM PowerPC computer that runs Mac software and vice versa - a situation unimaginable five years ago. Motorola will be free to sell the PowerPC processor to other manufacturers, allowing users to mix and match hardware and software from different manufacturers in a way that is currently impossible.
This 'open systems' approach is a philosophical change of heart for Apple and IBM, whose products have always been incompatible. 'We're like ex-smokers,' IBM's Steve Walker said.
Intel's response has been to concentrate on its one clear advantage - 100 million installed Intel-based PCs worldwide and the vast library of software that is compatible with Dos and Windows.
Intel also argues that PowerPC is not as open as claimed. The one operating system that the hardware cannot run is Dos, the most important operating system of all. Dos is so reliant on the design of Intel's processors that it is virtually impossible to rewrite it for any other type of processor. And as Windows relies on Dos to perform basic system functions, it rules out running directly all Dos and Windows software.
But Apple and IBM think they have a solution. Although the PowerPC chip cannot run Dos, the system can be fooled into acting as though it is.
This 'pretending' is a techique called 'emulation', in which one computer is programmed to take on the characteristics of another. Apple and IBM use slightly different emulation techniques, but the basic principle remains the same.
Apple uses a program called Softwindows which duplicates the internal functions of an Intel processor. It even allows you to run Mac and Windows applications side by side on the same computer and exchange information between them - something that cannot be done on any Intel computer.
Intel argues that emulation slows the processor down. The big gamble for Apple and IBM is that the PowerPC's sheer speed will compensate for this.
IBM has launched two workstation computers using PowerPC processors, but Apple's new machines are the first mass-market personal computers. These will start at about pounds 1,500 compared with almost pounds 3,500 for a comparable Intel system. This has prompted Intel to announce price cuts of about 20 per cent on its processors.
But it is the question mark over the PowerPC's performance that will make this the most important product launch in Apple's history. If PowerPC lives up to the claims made for it, then it could be, as Mr Walker put it: 'The key to the future of computing.' If not, Intel and Microsoft may even strengthen their hold on the market, having discredited PowerPC's claim to 'openness'.
Initial tests on Apple prototypes indicate that the first PowerPC chip, the model 601, at least equals the speed of Intel's new top-of-the-range Pentium processor. Two further chips, the 604 and 620, three and fives times faster than the 601, are planned. This kind of computing power is necessary to develop new technologies such as voice recognition and multimedia.
Intel's massive user base will not disappear overnight, but industry observers estimate PowerPCs could take 30 per cent of the market within four years. By that time Intel's range of processors will be nearing the end of its life and PowerPC could lead the computer industry into the next century.
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