X-bit labs

AMD: Per Aspera Ad Astra (page 3)

Category: CPU

by Victor Kartunov

[ 03/31/2004 | 06:54 AM ]

The Show Must Go On

Let’s try to think of possible steps AMD is likely to make. Of course, the reaction to Intel’s actions should be as simple to realize as possible and should also bring tangible marketing profits (sometimes that’s more important for the sales results than real technical advantages). So:

1. Dual-channel memory and the Socket 939 platform. The transition to these two things had been announced beforehand and looks quite logical. On the other hand, this is a bad reaction as contains no surprises – this transition is only expected to give some performance gains. We’ll discuss the problem of memory in the next section of the review. For now, let’s say it once again – this is a poor answer to Intel.
2. DDR2 memory. It cannot make a quick and ready answer since requires a serious overhaul of the processor and mainboards. The very necessity of DDR2 memory for the Athlon 64 is arguable – we’ll return to this subject shortly.
3. CPU frequency growth (building a performance reserve). Today, it is difficult to develop Athlon 64 (Opteron) processors faster than 2.4GHz using the 130nm + SOI technology. The current core seems to have its frequency ceiling somewhere around 2.4GHz and it would be very hard to overcome this limit and have an acceptable chip yield. Of course, we’ll see some operational 2.4GHz (and faster) dies, but I doubt they will be a mass product. AMD will probably have prepared a handful of samples for the announcement of the new platform, but they won’t be cheap and widespread. Overall, such processors will come into the mass market only after the company has switched to the 90nm + SOI technology, scheduled for the Q3 of this year. Thus, the frequency growth is no answer to Intel, as Intel’s marketing machine will be busy trumpeting the PCI Express and DDR2 as “the bus and memory of the future”, respectively, just around that time. The answer is needed sooner.
4. Expanding the L2 cache involves too many problems: the model with 1MB of cache is already large (193 sq. mm – what shall we expect from a larger cache?) and the necessity of redesigning the cache controller won’t be an easy matter. Moreover, larger cache requires more time to be accessed. The example of the Pentium 4 XE shows us that 2MB cache is welcome in the server market, but gives little profit for the desktop PC. This may be an option for the Athlon 64 FX and Pentium 4 XE, which are “extreme processors for extreme people” by their definition, but not a mainstream solution.
5. Speeding up the HyperTransport bus should bring some benefits, although their scale is hard predict. This idea seems to be good and easily realizable since the Socket 939 platform is not yet announced. They can just correct the specifications (by either changing the base frequency from 200MHz to 250MHz or increasing the bus multiplier from 4x to 5x) and all new systems will support this clock rate.

At first, the idea of a faster bus seemed improbable to me, I didn’t believe it at all. At first sight, this is really unnecessary: the current realization of the HyperTransport bus provides enough bandwidth. On closer examination, the idea seems viable. Why not?

So what does AMD get from speeding up the HyperTransport bus? First of all, the bandwidth will grow from 6.4GB/s, which Intel’s current bus also provides, to 8GB/s, which the competitor will only have after realizing its 1066MHz bus, not very soon. That’s an advantage, especially from the marketing point of view. Second, and that’s even more important, we enforce the winning aspect of the Athlon 64 architecture – the low data exchange latencies. By increasing the bus carrier frequency from 800MHz to 1000MHz (25%) we reduce the latency by the same 25%. Third, there’s one more marketing advantage: what sounds better – 1.6GHz (the previous version of the HyperTransport) or 2GHz? And AMD will beat Intel with Intel’s own weapon: earlier, the 800MHz Quad Pumped Bus of the Pentium 4 platform stood against the 400MHz bus of the Athlon XP one. I guess it’s clear who used to win from the comparison. Now these 800MHz of the QPB will stand next to the beautiful and round number, 2GHz! The advantage of AMD’s bus will look simply overwhelming in the eyes of an inexperienced user, who’s not versed in technicalities.