Pentium 4 review - the chips are down

Intel's hype machine is busy telling the world how much faster the internet is with its new Pentium 4 processor, but what does the next-generation chip architecture really have to offer? To work out what's really going on we've got our hands on a P4 Windows 2000 test system built by Intel. While this machine is not for sale, it's useful for vnunet.com to use as a test platform on which we can put the Pentium 4 through its paces.

Our test system came with a 1.5GHz processor installed on an Intel 850 motherboard and 256MB of memory provided by two sticks of 400MHz RDRAM.

This leaves a further two slots, and one memory channel, free for future expansion, but unfortunately, the upgrade choices aren't quite as flexible as they may at first seem. RDRAM has the restriction that each channel must be filled. For this board, it means that memory must be installed in identical pairs. This restriction can make further upgrades costly, as existing memory may have to be discarded to accommodate upgrades.

A more immediate problem is the relatively expensive cost of the memory itself. Rival technologies, such as double data rate (DDR) memory, currently sell for around 20 per cent more than standard SDRAM, which makes them considerably cheaper than RDRAM. However, Intel has no plans to provide support for such memory technology until part way through next year.

However, its not all bad news as RDRAM does take advantage of the new 400Mhz I/O bus that the Pentium 4 uses. As memory is often the slowest part of systems, speeding up access to match the ever-growing processor speeds is becoming increasingly vital.

The new bus also gives access to more bandwidth when peripherals such as PCI cards are accessed.

Also present on the motherboard is an AGP 4x slot, which helps make this system a good platform for gamers.

As advanced as the motherboard is, it's the changes in the processor that really make the difference. Most of the improvements are designed to make the chip deal more intelligently when executing programs. Raw GHz speed is not a good indication of how fast a processor really is; it's a combination of this and processor micro architecture optimisation.

For the Pentium 4 Intel calls the updated micro architecture its NetBurst technology. The improvements mostly revolve round the chip's pipeline. A pipeline is a list of instructions that have to be executed. While the processor is executing one instruction it can be at work on the rest of the pipeline performing tasks such as memory fetches. The new processor, with 20 instructions, has double the pipeline capacity of the Pentium III.

Working with this new architecture is an intelligent engine for filling the pipeline. Programs often reach points where two pieces of code can be executed, based on the outcome of a test; this is called a branch.

A pipeline has to guess the outcome of a branch before the test is executed. If the wrong guess is made the pipeline has to be emptied, and the process started again. The Pentium 4 has a higher success rate at guessing the outcome of such instructions, so less time is wasted flushing out the pipeline.

With the increase in speed gained here, it's important that system caches operate faster as well. For this processor the L2-cache - this sits between the processor and the memory - has been upgraded to transfer data in blocks of 64 bytes. However, while this is good for large transfers, if only one byte is needed, then the whole transfer wastes time. In situations such as this the Pentium III can outperform this processor.

For a more in-depth look at the technology behind this processor look at our in-depth whitepaper.

While all the improvements sound good, it's only under labs testing that the real answer becomes clear. We loaded the machine with Sysmark 2000, which gave us an impressive score of 203. This places this system near the top of recent performance leagues.

Unfortunately, it's not quite so cut and dried. Further tests using Windows 98 showed that the Sysmark performance figure dropped by 20 points. However, part of the reason comes from this benchmark not being optimised for some of the new features of the processor.