Review Today, Intel's officially released Pentium CPUs that offer both high clock speeds and dual-core loveliness, although you won't get both in one package. The Pentium 4 660, which is a 3.6GHz 'Prescott' chip with 2MB of L2 cache, will now be play second fiddle to the Pentium 4 670. All the same internals; just 200MHz faster and, obviously, more expensive. On the other hand, the near-£700 3.2GHz HyperThreading-capable Pentium Extreme Edition 840 gets a little brother. The Pentium D 820 runs in at 2.8GHz, is dual-core, but does not support HyperThreading. The end result is a dualie that comes in at a more palatable £200 or so. Which is better: high clock speed and HT (the 670) or relatively low MHz and two cores (the 830)? Are either of them worth it?

The 500-series P4s carried 1MB of L2 cache, an area of on-chip memory that stores data for the thread currently being executed. Running at full core speed, accesses to L2 cache are orders of magnitude faster than getting data from the system memory. Generally-speaking, the larger the cache, the better, though after a point adding more makes increasingly little difference. Gaming, in particular, sees a boost with larger on-chip caches. The Pentium 4 670 has 2MB of L2. Adding an extra 1MB of cache pushes up the 600-series' transistor count to around 169m, around 35m more than a 500-series part. The cost is inevitably passed on to the consumer. A Pentium 4 560J weighs in at around £270. The equivalently clocked 660 hits the wallet for £380.

The P4 670

All 600-series P4s support what Intel terms C1E Halt State. Put simply, with an appropriate OS and motherboard BIOS to activate it, C1E drops the CPU's multiplier and voltage to lower levels when a HLT (halt) command is issued. It makes implicit sense; why run at full speed and voltage when the system is just ticking over? Once an application demands CPU power, the voltage and multiplier are raised back to performance levels. There's also Enhanced SpeedStep (EIST), which is similar to C1E, and Thermal Monitoring 2, which intelligently reduces clock speed and voltage if the CPU begins to overheat.

The 600-series also benefit from Intel's AMD-like 64-bit extensions that allow the CPUs to run 64-bit operatings systems and applications. Windows XP 64-bit has already shipped and drivers are slowly but surely getter better. NX Bit, when implemented, stops code from being run in certain areas. It looks great on paper, but the majority of naughty viruses use more creative ways of execution.

The 670 is still stuck on a 200MHz frontside bus. It's strange that Intel chipsets have supported a 266MHz FSB for some time now and DDR 2 SDRAM is hitting the 400MHz mark with ease, yet all P4 processors barring Extreme Editions run at 200MHz. A 3.73GHz (14 x 266MHz FSB) model would have been appreciated.

The 670 has a TDP of around 115W. Cooled by an Intel reference copper-bottomed design, the processor hit 66°C running. It's one toasty CPU.

The PD 820

Better suited to most users' pockets than the pricey Pentium Extreme Edition will be a trio of dual-core CPUs without HyperThreading that all go by the Pentium D moniker. The bottom of the pile, so to speak, is the Pentium D 820, which runs at 2.8GHz. Next up is 830, pushing along at 3.0GHz, and then there's 840, running at an XE-matching 3.2GHz but, and it bears repeating, without HyperThreading.

Intel's 'Smithfield' line-up has two cores on a single die, each core with access to its own 1MB of L2 cache. But both cores share the same system bus, so memory bandwidth implications come more into play here than on a single-core setup. There are also the extra goodies that make it on to the Pentium 4 670, namely EIST, C1E and TM2 for power-saving, EM64T for 640bit processing, and Execute Disable Bit.

Intel's dumbed down the Pentium D line by withholding HyperThreading support. It's supposedly why the Extreme is extreme and the far cheaper Pentium D a not-so-extreme CPU. However, with two cores on a single CPU that can tackle a thread at the same time, HyperThreading won't be as missed as it would have been if absent on a single-core model, especially if you don't run more than a couple of CPU-intensive programs at any one time.

Intel hopes the clinching factor for the Pentium D is its attractive price. Ally that to a cheap-ish motherboard - say, any derivative of the 945-series - and it's dual-core action on the (relatively) cheap. AMD, on the other hand, is comfortable with the performance of its single-core Socket 939 CPUs, so the X2 range starts and finishes at the top-end of the market.

It's abundantly easy to see where the Pentium D 820 will succeed and fail, if judged by single-core models. Applications that are multi-threaded in nature will fly along, with two individual cores each executing concurrently. Think of professional apps and various media-encoding activities. Single-threaded applications will only be able to make use of part of each processor's ability so, for example, games won't be Pentium D 820's strongpoint. It'll run like a 2.8GHz 600-series CPU, if one existed. More importantly than ever, you need to evaluate your primary uses and then select the appropriate CPU. The Pentium D 820 has a TDP of around 95W. It hit around 58°c when under OS load and cooled by Intel's reference heatsink/fan combination.

A couple of things to note before we get on to the benchmark graphs. Firstly, the Pentium D 820's aggressive pricing puts it in line with AMD's single-core Athlon 64 3500+. Be sure to check out their relative performance. The Pentium 4 670, on the other hand, is slated to hit upon the current Athlon 64 FX-55's pricing territory. So it's pricey single-core against cheap dual-core.

Let's hit upon ScienceMark 2.0's memory bandwidth and latency first. It's usually a decent indicator of overall performance, but the release of dual-core models puts its predictive ability at risk.

Nothing much to choose between single- and dual-core Intel models here. They both share a single system bus, though. AMD's Athlon 64s always come out on top here.

Access latency has always been an Athlon 64 forte. Note that the use of Corsair's low-latency DDR2 SDRAM has reduced most LGA775 CPUs' memory access latency to under 80ns.

Our cryptography benchmark is also single-threaded. That's precisely why the Pentium 4 670, with its 3.8GHz clock, does relatively well. Pentium D 820 is the slowest of the bunch, which includes a 3GHz 500-series Pentium 4.

KribiBench, however, is multi-threaded. That means the Pentium D 820's can load up a couple of threads at a time and execute concurrently. With that in mind, the £200 CPU is faster than any single-core Pentium 4 and Athlon 64 in the line-up. You can patently see where its strengths lie.

picCOLOR, an image analysis program, also shows better performance when two cores can be used in tandem. See how the PD 820 is almost as fast as a 3.8GHz P4 570, and only narrowly behind the £500 670. It's also faster than its direct AMD counterpart, the Athlon 64 3500+.

A multi-threaded (and HT-aware) version of LAME also shows just where the PD 820 is good.

The multi-CPU render from CINEBENCH 2003 benefits CPUs with Hyper-Threading and, to a larger degree, those with two cores. Again, all single-core models in the test are left wanting.

Gaming is one area where dual-core CPUs come unstuck. As games tend to be single-threaded, you end up having each CPU only being taxed at up to 50 per cent. That's precisely why the Pentium D 820 looks poor in 3DMark2001SE's default test. The 670, though, just inches up Pentium 4's performance to within a thousand marks of an Athlon 64 4000+. The FX-55, though, is comfortably fastest.

Doom 3 performance generally mirrors that of 3DMark2001SE.

Our UT2003 bot test is more of a system bench than a GPU crusher. It requires a huge sub-system. The single-core Pentium 4 670 is barely faster than an Athlon 64 3500+, and the Pentium 4 820 is again the slowest of the bunch.

Lastly, Far Cry, tested with the in-game settings turned up to very high detail. As a rule, equivalent Pentium 4s don't perform as well as Athlon 64s in gaming, and dual-core models' performance is rarely better than a single-core's, although the untapped CPU power comes in handy if you're really into CPU-intensive multi-tasking.

Verdict

What are the lessons to be taken away from the launch of two new Intel CPUs? Taking the Pentium 4 670 first, its 3.8GHz clock speed, single-core design and high power requirements when under load make it the last of a dying breed. Performance-wise, it's around five per cent faster than the 660, and is either generally slower than AMD's Athlon 64 4000+ and FX-55 CPUs in applications that don't take full advantage of Intel's HyperThreading technology. The likes of Dell will dress it up to be the must-have CPU for an ultra-powerful machine, but unless professional applications or video editing are where you spend most of your time, it would be prudent to look towards AMD's top-end Socket 939 CPUs.

The Pentium D 820 is in a different league, both in terms of architecture and pricing. When viewed with respect to single-threaded applications, and gaming is counted amongst them, it's labouriously slow and ineffective against both its Pentium 4 single-core counterparts and, more importantly, AMD's Athlon 64s. Gamers and enthusiasts who value framerates above all else will need to look elsewhere for their thrills and spills. 2.8GHz of Prescott power isn't really enough to drive the subsystem-hungry likes of Far Cry and Half-Life 2 along at decent rates.

To state the obvious, where the Pentium D 820 thrives in is in multi-threaded applications that take full advantage of both its cores concurrently. When that happens, its performance beats out the fastest and most expensive single-core models with comparative ease. Above all else, what the £200 Pentium D 820 does is bring real dual-core goodness to the masses. Not withstanding its gaming performance, and with due knowledge that dual-core CPUs and multi-threaded applications are the way of the future, the Pentium D 820 is, I reckon, a better proposition than a low-end, single-core model. Now all we need to do is strap it into a retail motherboard that offers FSB adjustment, ramp up the voltage, and see what comes of it. Stay tuned.

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