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Later, as the technology is perfected, DDR2-400 with 3-3-3 timings will appear, but we’ll never see the 2-2-2 combination that high-quality DDR SDRAM modules can work at. And even no-name manufacturers offer 2.5-3-3 DDR SDRAM modules that have better characteristics than the technological triumph of DDR2! The following table lists DDR2 types in the order of their intended appearance in the market:

Memory

Preliminary latencies, Q3 2004

Latency, ns

Bandwidth, GB/sec

DDR400*

2.5 – 3 – 3

12.5

3.2

DDR500**

3 – 3 – 3

12.0

4.0

DDRII-400

4 – 4 – 4

20

3.2

DDRII-400***

3 – 3 – 3

15

3.2

DDRII-533

5 – 5 – 5

~19

4.3

DDRII-533

4 – 4 – 4

~15

4.3

DDRII-533***

3 – 3 – 3

~11.3

4.3

DDRII-667

5 – 5 – 5

15

5.3

DDRII-667

4 – 4 – 4

12

5.3

* DDR400 SDRAM data are included for the sake of comparison
** DDR500 SDRAM data are included for the sake of comparison. The DDR500 standard is not ratified by JEDEC
*** A later revision, expected in the second half of 2005

The table doesn’t need much commenting upon. It’s clear that only DDR2-533 with 3-3-3 timings is really better than off-the-shelf DDR400, but it will come out with timings like 4-4-4 or even 5-5-5. Only in the second half of 2005 we’ll have really fast memory with 3-3-3 timings. It is highlighted in the table as the first memory type to show the advantages of the DDR2 standard.

AMD reasonably thinks that it should introduce DDR2 into its processors starting from DDR2-667. Only this standard, even in its earliest modification, provides acceptable timings. But this memory is expected no sooner than the second half of 2005. Thus, the users of current Athlon 64 models shouldn’t be very disappointed about the lack of DDR2 support – they don’t miss anything important.

As AMD is not interested in the first versions of DDR2, we should think that this memory type will only be supported in the next core – why should they do extra work?

We must also understand that support of DDR2 will require new mainboards, both for Intel’s and AMD’s platforms. Particularly, the Socket 939 platform is not supposed to accommodate DDR2 memory. Thus, if you want to use this memory, you’ll have to wait for the next year and for DDR2-533 at least, otherwise you’ll get no performance advantages. It’s logical to think that AMD will offer its new platform in the next year (probably, in its second half). Will it be compatible with Socket 939 processors? I think not. Will the Socket 939 platform continue to evolve? I think yes and I’ll explain my opinion shortly.

By the way, there’s another curious side effect from the acceleration of the HyperTransport bus, omitted above. So, the carrier frequency of the bus will be 1000MHz. 1000MHz can be arrived at either by 200x5 or by 250x4. The second variant is interesting because of one bus-unrelated thing. Some memory makers, like Samsung or Hynix, have started producing DDR500 memory (this name is not official, as this standard is not approved of by JEDEC; it just means that the memory works at 500MHz). It seems like the two events are not connected – but they do fit together nicely. It’s easier for AMD to implement support of DDR500 than of DDR2. It’s also profitable for the manufacturers who can sell some memory at a high price not only to a few overclockers, but also to the mass user. There would be only one losing side – Intel. Intel doesn’t have to fear the transition to DDR2 – memory latency increases, but the latencies are anyway high on the Pentium platform.

Now let’s take a look at the table. DDR500 seems very appealing – only the later revision of DDR2-667 with small latencies can surpass it. Thus, AMD’s opinion becomes well-grounded: why should they transition to the new standard when the old one is not yet depleted? Moreover, DDR500 will be much cheaper than DDR2-667 with reduced latencies (today, there’s a difference of $3 between 256MB modules of DDR400 and DDR500). At least, this price proportion will keep in the near future.

 
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