Wednesday, January 31, 2001

Introduction

In this article, we'll be presenting you to the recently developed DDR266 memory standard, the DDR-compatible Gigabyte GA-7DX motherboard - which is based on the AMD761 chipset, and, last but not least, the newly released AMD Athlon "Thunderbird" 1.2GHz DDR266 CPU. As you can see, we've got a whole lot to talk about this time around, so let's say that we skip on down to the fun part and leave the intro behind.

DDR memory

Most of us have been well aware of the constant evolution of computer technology over the years. Newer, faster hard disk drive technologies have come to the forefront, more powerful processors have been developed, and newer generations of graphics accelerators are opening new doors in the world of graphics & video.

Memory technology hasn't bucked this trend either. In recent times, we's seen 66MHz EDO RAM replaced first by PC100 SDRAM, then 3-cycle-latency PC133 SDRAM, then PC133 memory with 2 clock cycles latentcy.

And, of course, we can't forget the ground broken by the introduction of RAMBUS RDRAM.

While Dual-Channel PC800 RAMBUS RDRAM has a maximum theoretical bandwidth of 3.2GB/sec, however, and thus has the potential to blow away its competition in the memory market, it has met with some difficulties. First, there is the problem of RDRAM's inherently slower (than SDRAM) latency. Next came the problems with Intel's i820 chipset, which couldn't take full advantage of all of RDRAM's potential benefits. The final strike against RDRAM, though, has certainly been its price, which remains considerably higher than competing memory standards. As a result of all this, there has been a considerable push in the industry to develop a memory standard capable of higher bandwidth than PC133 SDRAM, but of lower latency and price than PC800 RDRAM. The fruits of that labor come in the form of PC1600 (or DDR200), and PC2100 (or DDR266) DDR-SDRAM.

What are the benefits of this new standard, you may ask? Well, it's quite simple. First off, the letters "DDR" stand for "Double Data Rate", and indicate that the memory itself is designed to transfer data on both the rising and falling edges of each clock cycle. Traditional SDRAM, by comparison, only transfers data on the rising edge of each cycle.

Thus, in theory, DDR266 memory is capable of pushing up to 2.1GB/sec of bandwidth. This is actually lower than the theoretical limits of PC800 RDRAM, but, funny enough, DDR266 memory performs noticeably as good as the former. It's sales price is also comparably less expensive than the former, which makes it a much more reasonable alternative.

Physically, a stick of DDR SDRAM has a single notch, which was a change from the dual-notch configuration of PC133 DIMMs with which we are all familiar with. The memory latencies of DDR SDRAM are also a bit odd-ball, as they typically come with values such as CAS 2.5, CAS 2 or CAS 3 rather than CAS 2 or CAS 3, as is the case with PC133 SDRAM.

DDR SDRAM comes packaged on a 184-pin DIMM and draws 2.5v, rather than the 168-pins and 3.3v of its SDR SDRAM forbearers.

As for performance comparisons, DDR266 takes the cake over PC133 memory, with a typical performance lead of 10-15%. More on this in our memory benchmarks...

Next: The AMD Athlon T-Bird 1.2Ghz processor.