If memory serves...

Perusing the specifications of today's PCs, it's obvious that Double Data Rate (DDR) has become the dominant memory technology.

While DDR has long been the preferred memory for AMD systems, it's impressive to see how quickly it has been adopted by Pentium 4 platforms, especially when you consider that, until recently, the Pentium 4 had no choice but to use RD-Ram.

Times change quickly though, and today there's the choice of several DDR chipsets for the Pentium 4. So where does that leave RD-Ram? In the face of ever-increasing DDR memory speeds, will this highbrow technology disappear?

As far as Rambus is concerned, its RD-Ram technology still has a long and defined roadmap. Indeed, at this June's Computex show in Taiwan, the fastest performing system was sporting an entirely new RD-Ram development: 32bit PC4200.

Until this point, all RD-Ram PC solutions were 16bit technologies, which meant Rimm memory cards had to be installed in matching pairs. Today's 16bit RD-Ram is commonly available at speeds of 800MHz and 1,066MHz and is known as PC800 and PC1066; they deliver data rates of 1,600MBps and 2,132MBps respectively.

The only current chipset supporting RD-Ram is Intel's 850E, which - like the 850 and 840 before it - is a dual-channel solution. The data throughput of all the above is effectively doubled, with pairs of PC800 and PC1066 RD-Ram Rimms delivering 3.2GBps or 4.2GBps respectively.

These neatly match the system bus speeds of the Pentium 4 processor which, at 400MHz or 533MHz, also works with 3.2GBps and 4.2GBps of data respectively. It's no wonder - in terms of numbers anyway - that dual-channel RD-Ram is a perfect match for the Pentium 4, as PC2100 (266MHz) and PC2700 (333MHz) DDR memory deliver just 2.1GBps and 2.7GBps respectively.

So where does new PC4200 RD-Ram memory fit in? Like PC1066 RD-Ram, it runs at 1,066MHz and is designed for processors with a 533MHz system bus.

When coupled with the dual-channel capabilities of an Intel 850E chipset, it will also deliver the same 4.2GBps of data. The big difference between PC1066 and PC4200 is that the latter is a 32bit technology, which means Rimm memory cards can be installed singly.

Effectively, a 32bit Rimm is like two 16bit Rimms back-to-back on a single card. The interface is physically incompatible though, with 32bit Rimms sporting 232 pins. Note that 800MHz 32bit Rimms are also available, often called PC3200, but not to be mistaken for DDR 400, which is also known as PC3200.

Does RD-Ram still outperform DDR, and is it the best match for the Pentium 4, especially in its latest 533MHz system bus guise? We decided to find out by building and comparing a PC4200 RD-Ram system to one using PC2100 and PC2700 DDR.

Choosing a motherboard for PC4200 is certainly very simple, as at the time of writing there was only one: the Asus P4T533. We sourced one of the first models and fitted it with a single 512MB Samsung PC4200 RD-Ram Rimm.

For the DDR platform, we chose an Asus P4B266-E (Intel 845D chipset) with 512MB of Crucial PC2100 DDR memory. We also tested a DFI NB76-EA (Intel 845G chipset with onboard graphics disabled) with 512MB of Crucial PC2700 DDR memory.

We completed each system with a Creative Geforce3 graphics card running the Nvidia Detonator 28-32 drivers, and a 15GB Seagate UltraDMA100 hard disk, formatted with Fat-32 and installed with Windows XP Professional.

We tested all three motherboards with a 2.4GHz Pentium 4 in both its 400MHz and 533MHz system bus versions, identified by either an A or B respectively. Cooling was provided by an Alpha PAL8942T heatsink and a Papst 8412 NGML fan - more of which later.

Results
Our first tests were using the Pentium 4 2.4A processor, running on a 400MHz system bus. The Asus P4B266-E motherboard, fitted with PC2100 CAS 2.5 memory, scored 217 in Sysmark 2002. This broke down into 303 for Internet Content Creation and 156 for Office Productivity, and from this point on, such a score will be written as 217 (303/156).

Switching to the DFI NB76-EA motherboard, again with PC2100 CAS 2.5 memory, and the score increased to 230 (320/165); we assume the difference between this and the above is due to the different chipsets.

Over to the Asus P4T533 motherboard, which with a Pentium 4A processor was driving its PC4200 RD-Ram at 800MHz - this was now effectively acting as PC3200 RD-Ram. The Sysmark 2002 score here was 243 (333/178), which is around five per cent faster than the DFI and 12 per cent faster than the Asus DDR solutions.

Note that in all the RD-Ram tests, the memory was used at its Turbo setting in the Bios.

We then performed the tests again with the Pentium 4 2.4B processor, running on a 533MHz system bus, but didn't include the Asus P4B266-E as it was not officially certified to handle Pentium 4B CPUs.

The DFI NB76-EA actually scored the same with the Pentium 4 2.4B chip as it had with the Pentium 4 2.4A, namely 230 (320/165). Could the limiting factor have been the PC2100 CAS 2.5 memory? We switched to our PC2700 CAS 2.5 Dimm to see.

Fitted with the faster memory, the score increased, but only by three per cent to 237 (326/173). Note that we needed to update the Bios on the DFI board before it offered a DDR333 (PC2700) option.

CAS memory latency rating plays an important factor in performance. To see a greater benefit from PC2700 memory, you'll really need to buy the faster CAS2 variety and change the timings in your Bios. Sadly, this wasn't available at the time of writing, but we did try a CAS2 PC2100 Dimm, which scored 232 (321/168).

This brings the difference between CAS2 PC2100 and CAS2.5 PC2700 to just over two per cent (on the DFI board anyway).

So back to the Asus P4T533 motherboard which, when fitted with a Pentium 4B processor, could now drive the PC4200 RD-Ram memory at its full capabilities.

This time, Sysmark scored 255 (340/191), which is five per cent higher than the Pentium 4A PC3200 RD-Ram configuration.

Since Intel charges the same for Pentium 4A chips as it does for Pentium 4Bs, the latter are preferred so long as you're coupling them with memory that can keep up - and that means RD-Ram rated at 1,066MHz.

From our tests on the DFI board with an Intel 845G chipset, there was no difference between using the Pentium 4A and Pentium 4B with PC2100 memory, and only a fractional improvement when fitted with PC2700 memory.

Overclocking
It wouldn't be a typical edition of Hands On Hardware without some overclocking, and we hoped this would greater reveal the benefits of RD-Ram. In last month's issue, we took a Pentium 4 2.4A processor and overclocked it up to 3GHz, by increasing the system bus from 400MHz to 500MHz, and supplying an extra 0.25v of core voltage to the chip.

We had used the Asus P4B266-E motherboard with a stick of PC2100 memory, and by increasing the clock speed by 25 per cent, had seen the Sysmark score increase by 13 per cent. Not bad, but not great either, considering the whopping 3GHz clock speed.

With its system bus speed overclocked from 400MHz to 500MHz, our '3GHz' chip was now trying to shift 4Gbytes/sec, but the PC2100 memory was only capable of half this throughput. Clearly the memory bandwidth was the limiting factor.

We returned to the Asus P4T533 RD-Ram motherboard and refitted the Pentium 4 2.4A processor, which, when normally clocked, had scored 243 (333/178). Increasing the system bus from 400MHz to 460MHz resulted in a clock speed of 2.76GHz, and a Sysmark score of 275 (383/197).

Increasing the clock speed by 15 per cent had increased the Sysmark score by 11.5 per cent. On the previous DDR system, increasing the clock speed by the same 15 per cent had only resulted in a Sysmark increase of just six per cent. Clearly the RD-Ram had continued to match the processor's requirements, while DDR was struggling to keep up even when clocked normally.

Out of curiosity, we tried overclocking with the Pentium 4 2.4MB processor on the RD-Ram system, but quickly hit a wall. The problem was that with a 533MHz system bus as standard, it was already pushing the PC4200 RD-Ram as hard as it could officially go.

We managed to edge the clock to 2.52GHz with a system bus of 560MHz, and produced a result of 264 (358/195). Sadly, increasing the system bus further just pushed the RD-Ram too far beyond its capabilities. With a slower system bus of 400MHz though, the Pentium 4A processors can, in theory, be overclocked by up to 33 per cent before they hit the official limits of PC1066 or PC4200 RD-Ram.

The morals of these tests follow: if you're not into overclocking, the Pentium 4B processors run a bit faster than the Pentium 4As, but only when coupled with memory that can keep up - right now, that means PC1066 or PC4200 RD-Ram.

If you are into overclocking, then RD-Ram is required to keep up with a fast Pentium 4, but go for the Pentium 4A versions, as these can be pushed by up to 33 per cent before they reach the limits of PC1066 or PC4200 RD-Ram.

Which memory?
In short, while a Pentium 4 coupled with DDR memory can produce a great system, you won't see the best from this processor unless you're using RD-Ram.

At the time of writing, the price difference between the two memory technologies was closer than ever, with 256MB of PC2700 DDR and PC1066 RD-Ram costing £61 and £105 respectively - that's less than £100 extra for 512MB of RD-Ram compared to PC2700, which isn't much on a high-end system.

The long term future of RD-Ram on desktop PCs remains uncertain though: despite a new chipset from Sis, Intel hasn't committed to replacing its 850E, and we can't guarantee you'll find it easy to buy 'cheap' Rimms in a year's time either.

At the same time DDR isn't standing still, with DDR400 chipsets already here and dual-channel solutions from Intel expected in a year. If you want to build or buy the fastest Pentium 4 system today though, PC1066 or PC4200 RD-Ram memory comfortably beats PC2700 DDR and is worth the extra money.

Silent cooling
As more and more people work from home or in small offices, or try to integrate PCs into their living rooms, noise becomes a major concern.

PCW Labs writer Leo Waldock tested some of the trendiest silent cooling accessories on the market - including the Zalman Flower Cooler, which consists of an elaborately designed heatsink and a large fan which is mounted from above.

The idea is that a large slowly spinning fan can produce the same airflow as a small high-speed fan, but with much less noise. The 92mm fan Zalman supplies is clearly too large to fit on top of the heatsink, hence the bracket mount, but this also allows for an unusual heatsink design and eliminates vibration between the two.

It additionally delivers cooling to nearby components such as the chipset, memory and graphics card.

While the Zalman Flower Cooler definitely works, we've recently discovered some alternative solutions that are, shall we say, a little more conventional looking. The theory remains the same: employ a large, slow-spinning fan on an already highly efficient heatsink.

The Alpha PAL8942T heatsink is a beast of a cooler that takes an 80mm fan which you must supply yourself. We had been employing a Delta FG-001-DE fan in order to perform some serious overclocking, but to generate a huge 68.51 cubic feet per minute meant tolerating a 48.5 decibel (dB) racket. This combination really is as noisy as it is cool.

Out of curiosity, we wondered how the Alpha heatsink would perform in normally clocked conditions with a more modest fan. We chose a Papst fan, as these are renowned for their quiet operation. The 8412 NGML FG-000-PA model is rated at just 19dB, but would its 26.5 cubic feet/min airflow be sufficient to cool a modern Pentium 4?

We fitted the Papst fan instead of the Delta on our test system that used a Pentium 4 2.4A processor. Previously, the Delta fan had cooled this chip to a remarkable 33 degrees. Much to our surprise and relief, the Papst fan maintained temperatures of 34 degrees. Even when the CPU core voltage was increased from 1.5v to 1.75v for overclocking, the temperature didn't increase beyond 42 degrees.

Admittedly, the Delta fan had maintained an impressive 36 degrees at this core voltage, and allowed the CPU to be overclocked that bit further, but the point was that the Papst fan was sufficiently cool for normal or modest overclocking, and more importantly was virtually silent.

In fact, perusing the Zalman specification reveals that its 92mm fan produces 36dB in normal 2,800rpm mode, and 20dB in silent 1,600rpm mode.

In comparison, our unexotic Papst fan was rated at 19dB. The general consensus is that 20dB or lower is as good as silent in a typical home, especially if the device is located a few feet away or more. It would be hard to measure much difference in noise between the Zalman and Papst solutions, but we were certainly pleased to virtually eliminate CPU cooling noise from such a conventional-looking device.

We sourced the Alpha PAL8942T heatsink and Papst fan from Overclockers UK for £34.65 and £10.65 respectively. Overclockers is also reporting good results from combining the more recent Thermalright AX7 heatsink (£29), with an even quieter Papst fan, which produces 19.4CFM with a claimed 12dB noise rating.

We've even heard of some enthusiasts who have experimented with underclocking their CPUs to allow lower core voltages, and subsequently even more modest cooling solutions - some have even reported success with fanless passive cooling, although we view this with extreme caution.

Of course, a silent CPU cooler is absolutely pointless if the rest of the system is making a racket. We're currently conducting tests to produce a silent PC designed as a home entertainment centre, but in the meantime we recommend checking out Quiet PC, which sells silent coolers for CPUs, graphics cards and chipsets, along with quiet power supplies.

We're still not entirely happy about enclosing a hard disk to reduce noise though, and instead advocate choosing a quiet drive from the outset, such as one of Seagate's Barracuda ATAIV models.

It's certainly an interesting tide of change that noise-sensitive users are deliberately selecting lower-speed processors in order to employ quieter cooling solutions. After all, most of us could honestly put up with Office or Quake performing a few per cent slower in exchange for peace and quiet, not to mention a cheaper processor.

Until we can report further on alternative solutions, we can highly recommend the combination of a large heatsink (such as the Alpha), coupled with an 80mm Papst fan - virtually silent but still very effective.