Articles: CPU
 

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You see that DDR500 is most efficient for 2.0GHz and 2.2GHz processors as well as, to a lesser extent, for 2.4GHz CPUs. These are the frequencies the CPUs are going to have in the near future. These processors will experience a nice speed boost from their memory subsystems. By the way, the frequencies specified above will be applicable to both platforms as it’s quite probable that the new revision of the Athlon 64 will come out for the Socket 754, too. Anyway, the difference between DDR400 and DDR500 is quite perceptible and should be conspicuous in benchmarks and real applications.

Variant B: 1000 = 250 x 4

That’s a less probable variant, but more interesting due to its consequences.

Consequence One: the CPU frequency will be adding 250MHz, rather than 200MHz. That’s a wide step and the K8 core cannot be scaled up infinitely, so it makes sense to use half-integer CPU multipliers. Then Athlon 64 CPUs will be able to add 125MHz and their model range can change with 200+ stepping. This allows keeping up with the traditional for this platform ratio between the frequency growth and the model number. The supposed relation between the frequencies and models (for Socket 939) is listed in the following table:

2.0GHz

2.125GHz

2.25GHz

2.375GHz

2.5GHz

2.625GHz

2.75GHz

3200+

3400+

3600+

3800+

4000+

4200+

4400+

So we’ve got a logical series. Let’s see what we have with memory with such “not-integer” frequencies:

Frequency, GHz

DDR400

DDR500

2.0

200MHz (10)

250MHz (8)

2.125

193.2MHz (11)

236.1MHz (9)

2.25

187.5MHz (12)

250MHz (9)

2.375

198MHz (12)

237.5MHz (10)

2.5

192MHz (13)

250MHz (10)

2.625

202MHz (13)* or 187.5MHz (14)

238.6MHz (11)

2.75

196.4MHz (14)

250MHz (11)

* Although the memory divisor of 13 gives a higher memory frequency than 200MHz, the difference of 2MHz is small enough to affect stability in any way. That’s why we think this divisor should be used, rather than the formally necessary 14.

Well, it’s not all smooth with the memory frequency – it is always faster than the nominal, however slightly. DDR400 is not very effective, while DDR500 is, although DDR400 is closer to the nominal frequency than DDR500 in percent expression.

Once again, this variant is less probable as DDR500 is still an exotic memory type today. It’s not quite discreet to put your main stake on exotic memory. So we should get prepared to the first variant when the bus is closed with a frequency of 200MHz. DDR500 can show its advantages with this variant, too.

By the way, if the chipset allows, the overclocker may consider the option of transforming Variant 1 into Variant 2. This transformation should bring high dividends. And really, making the CPU work at 2.25GHz rather than 2.0GHz, and memory at 500MHz rather than 400MHz, and the HyperTransport bus at 1000MHz rather than 800MHz (i.e. clocking it as 250 x 4), we’ll get a nice performance boost. There’s only one nuance: for this overclocking to become possible, we need that AGP and PCI frequencies were asynchronous to the HyperTransport clock rate. Well, NVIDIA and VIA, two major manufacturers of chipsets for the AMD platform, are both promising to implement async clocking in their new products.

 
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