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The X2 :::...

AMD have no intentions of converting their entire portfolio to dual-core, not yet at least. At the moment they have a very specific market sector in mind for their X2 processors...

How it works:::...

I think we already know from experience that doubling up on hardware capability doesn't mean doubling up on performance. We've seen it with SMP, we've seen it with dual channel memory and we'll see it again with dual cores in some situations. The good news is that dual-core CPU's don't suffer the same crippling limitations we've seen in the past, so while it's easy to be cynical I think it's fair to say that for the most part, this is one technology that may actually deliver on its promises, at least in software designed rum multiple threads.

Even without support for multiple threads, we still get the ability to share the processing burden under perhaps the most important of scenarios from a mainstream user's point of view will be good, old-fashioned multitasking.

As a former dual-cpu user I understand the frustration felt by many current users that such a promising technology was given so little support. Gaming support in particular was flaky at best, and this is perhaps one of the areas where multiple processors could have really flexed a little muscle. I suppose the introduction of the X2 will at least nudge game developers a little closer to a multithreading mindset for future games if nothing else, perhaps with some heavy duty physics, realistic, deformable, interactive environments and who know what else all supplementing the GPU and moving us ever closer to a genuinely cinematic and encompassing gaming experience.

The diagram below doesn't really do justice to the level of complexity behind the X2, but for our purposes it says all we need it to. In it we see there are two CPUs, each with its own instruction and data cache quota and each with its own L2 cache. The Integrated memory controller serves both CPUs while HyperTransport plays its pivotal role with some 24 GB/second of bandwidth per core, all via an on-chip system crossbar. On paper this is far more efficient than the architecture employed by Intel's Pentium D and Extreme Edition dual-core part.

Despite the hype, the idea is nothing new. SMP (Symmetric Multiprocessing) veterans are no doubt smiling quietly to themselves at all this fuss over something they've been doing for years. What they may find less amusing is how much cheaper it is to buy an X2 than it is to buy a pair of vanilla A64s.

FSB No More:

This seems like the perfect opportunity to tackle the subject of AMD's Front Side Bus, or rather their lack of it. When it comes to overclocking the Athlon64, you may occasionally here us refer to the base frequency as the FSB. AMD are quite keen to point out however that the term isn't actually an accurate one when it comes to the way their architecture works.

Here's the rub. When FSB was genuinely FSB, data was sent specifically along this bus based on the frequency it was running at. AMD however have replaced this style of data bus with bi-directional full-duplex (send and receive at same time) 2GHz HyperTransport Link. Memory calls meanwhile are now handled directly on the CPU core, therefor even here we can't correctly use the term Front Side Bus. It should instead be the "CPU to Memory Controller frequency".

So what happens when we overclock? Well, what AMD would like us to say is that we've increased the speed of the clock generator, which of course is precisely what has been done. The fact that this clock frequency is used as a basis for the frequency off all the other components doesn't qualify it as a front side bus because no data whatsoever is transferred along it directly, therefor it's not technically a bus at all, it's a base frequency.

I, like many other reviewers will no doubt succumb to habit and refer to the "base frequency" as "FSB" from time to time. The fact is, it's no such thing.

Test System:::...

We were sent a complete system platform for testing, not because anything suspicious is going on, but because AMD had had a chance to test the motherboard and verify its BIOS support for the X2. The motherboard they sent us was the very nice A8N-SLI Deluxe from ASUS

ASUS A8N-SLI Deluxe

• Supports AMD Socket 939 Athlon 64FX/Athlon 64
  
• NVIDIA nForce4 SLI
  
• PCI Express Architecture
  
• SATA 3Gb/s
  
• Dual RAID
  
• Dual Gigabit LAN & AI NET2
  
• NV Firewall
  
• AI NOS™ Inject "nitrous oxide" into your CPU! The patented AI NOS™ (Non-delay Overclocking System) technology intelligently detects system load and automatically boosts performance for the most demanding tasks. Unlike other dynamic overclocking techniques, AI NOS™ reacts much faster to satisfy your unending need for speeds.
  
• AI Audio (8-channel Audio)

Crucial Radeon X850 XT

Graphics was handled by the extremely capable Crucial Radeon X850 XT PCI Express 256MB.

• Powered by RADEON™ X850 XT Series VPU, driven by 16-pipe rendering architecture
  
• Full support for DirectX® 9.0 and the latest OpenGL® functionality 256-bit DDR memory interface, featuring HYPER Z™ HD bandwidth-conserving technology
  
• 256MB GDDR3 memory
  
• 400MHz RAMDAC
  
• Native x16 lane PCI Express support
  
• VGA connector, TV-out connector

All, tests were performed using WindowsXP with service pack 2 installed. Graphics drivers were ATi's CATALYST 5.5 set for optimal performance.

Memory consisted of 2x512MB of Corsair XMS 3200Pro running at 2-2-2-5.