DDR vs. DDR-2 - IntroductionIntroductionDDR SDRAM has been the biggest savior for the Intel Pentium 4 platform. It has taken it from a status of "avoid like the plague" to one of total acceptance. During the Pentium 4's early life, Intel had a major hard time convincing its OEM and retail customers to purchase a Pentium 4 system simply because of expensive processors and not to mention an expensive and rather lacklustre RAM imitative called RDRAM.Licence agreements with Rambus put Intel on the back foot with DDR, as they had agreed to support the RDRAM series memory on their I850 Pentium 4 chipsets. This caused much uproar, as the price/performance or RDRAM was totally off the scales - nobody wanted to touch it with a 10 meter cattle prod. When these licensing agreements were over, Intel flooded the market with the I845x series chipsets. These all supported single channel DDR memory.Dual Channel DDR was the only way to satisfy the bandwidth hungry Pentium 4 processor, as its bandwidth of upwards of 4.2GB/s just couldn't be satisfied with a 2.7GB/s of DDR-333 memory.Now DDR has reached its maximum frequencies of around the 466MHz mark, and even then extra voltage is required in order to reach these speeds, and with the instability of some modules, it has become apparent that DDR is now at the end of the speed highway. It's now time for something else to take over that is somewhat faster, but not all that different that is causes the same performance problems RDRAM once did. Enter DDR-2.Today we pit DDR-400, the fastest JEDEC standard memory against the DDR-2 533MHz, the currently fastest DDR-2 JEDEC standard to see just what a system based on this memory can actually do.
DDR vs. DDR-2 - DDR2 in DetailDDR-2 in DetailPrepare yourself as we will be going into the heart of DDR-2 technology here.DDR-2 technology is a direct extension of the already popular and mature DDR technology. In fact, the reason DDR-2 and DDR is almost identically compatible and require minimal reconfigurations of the DRAM controllers is that is has the identical same command structure, just a slightly different way of going about its processing of the data. What does this all mean? Well let's have a look at the DDR-2 architecture and how it actually works compared to the DDR technology.DDR SDRAM uses a simple premise - it takes the existing command issue structure and DQ (or Data Queue) and allows the array to send two bits of data per clock cycle rather than the standard one of SDR. This is done by using both the rising and falling edges of the clock cycles, effectively allowing you to send twice the data at the same bus frequency. This is how DDR was able to get 200MHz rating while still using a 100MHz bus speed.DDR-2 uses the exact same sending technique, two bits per clock cycle, however, the internal memory cell array and buffers have been changed.
DDR vs. DDR-2 - DDR2 in Detail ContinuedDDR-2 in Detail ContinuedDDR-2 while having a similar command set, it requires a totally different memory socket. This is why DDR and DDR-2 modules can't be interchanged in the same sockets. DDR runs on a 184 pin socket, where DDR-2 uses a 240 pin socket. The extra pins are used for the second core on the chip as well as extra signal voltage pins. DDR-2 however, does give some advantages as it can be in a term retarded back to allow DDR memory modules to exist on the same motherboard as DDR-2. Some motherboards have appeared with both DDR and DDR-2 memory module sockets which just goes to show the similarities between the two technologies. Intel's own I915 series chipsets support both DDR and DDR-2 memory technologies. You can have Dual Channel DDR or Dual Channel DDR-2 and while you may find both sockets on the one motherboard, you can't use them both at once, as they share the same data address paths, and would simply conflict. However, it does allow users to go to I915 chipsets and keep their DDR until DDR-2 matures into a more mainstream product.DDR-2 does have its advantages over DDR, but it falls behind in one aspect - latencies or the time it takes to perform certain tasks. DDR runs at usually CL3, CL2.5 and some high performance modules run at CL2, though CL2.5 is more common for higher speed memories over 400MHz. DDR-2, due to its nature of dual cores increases latencies to CL5 and CL4 and for the higher performance modules CL3 although CL3 isn't available yet which makes CL4 the lowest available at the moment.This won't affect the Intel Pentium 4 series as much as it would the AMD series CPU's which seem to crave lower latencies rather than raw bandwidth which is one advantage for Intel as DDR-2 533 can offer 8.5GB/s and with 667 modules now starting at 10.5GB/. With DDR-2 speeds set to push bandwidth to the ultimate, you will soon see a lot of programs written for high bandwidth utilisation.DDR-2 possesses a slight complication in adoption for AMD64 users, as it simply cannot be done on the current 754 and 939/940 packaging. As most already know, AMD places its DDR memory controller and primary Northbridge onto the CPU die. While this does eliminate the need for a memory bus controller and CPU to system controller as AMD wanted, when new memory standards hit, it's slow to change over.With DDR-2 requiring a new socket and new pinouts, AMD will have to re-design its K8 CPU with a DDR-2 memory controller as well as a new socket, as extra pins will be required for the DDR-2 memory controller. When AMD swapped over from Single Channel memory in its 754 pin to Dual Channel Memory controller in the 939, the pin requirements jumped by 185 pins, the exact amount needed to add a second channel.So if AMD wanted to have a Single Channel DDR-2 and Dual Channel DDR-2 solution in the K8, we would have to see a socket 808 to replace the 754 and a Socket 1048 to replace 939 which is simply too much cost to the consumer, especially with the already super exorbitant prices of AMD K8 on the 939 package.
DDR vs. DDR-2 - The ModulesThe ModulesDDR-2, while not as fast on the uptake as DDR was, is starting to make its mark on the industry. While having one big partner behind you, it doesn't always guarantee an instant audience. DDR only had VIA on its side when it started and it wasn't really till Intel and SiS took the DDR bandwagon that sales of DDR memory really hit the roof - the same can be projected for DDR-2. Intel may be behind DDR-2 all the way, but with AMD sticking to DDR for the time being, it might face a slightly less than stellar sales margin. With that said, there are already a few modules on the market, and we were lucky enough to get our hands on some Mushkin DDR-2 modules rated for 533MHz.
DDR vs. DDR-2 - Benchmarks - Test System Setup and SiSoft SandraTest System SetupProcessor: Intel Pentium 560 3.6GHz (800MHz FSB) (Supplied by Spectrum Communications)Motherboard: MSI 915P Combo (Supplied by MSI)Hard Disk: 2x Maxtor Maxline III 250GB SATA (RAID 0)Graphics Card: Gigabyte GeForce PCX5900 (Supplied by Gigabyte)Operating System: Microsoft Windows XP Professional SP2Drivers: nVidia Forceware 61.77 and DX9cWe used the MSI 915P Combo for two major reasons:1) It has both DDR and DDR-2 memory sockets, allowing us to keep the platform unchanged in regards to graphics cards, CPU and the like2) Its overclocking was much higher than any other dual memory motherboard availableOn the settings side, we set the BIOS to run the memory at default timings by the SPD and at their maximum rated, so DDR was at 400MHz and DDR-2 was at 533MHz.SiSoft SandraVersion and / or Patch Used: 2004 SP2Developer Homepage: http://www.sisoftware.co.ukProduct Homepage: http://sisoftware.jaggedonline.com/index.php?location=home&a=TTA&lang=enBuy It Here
DDR vs. DDR-2 - Benchmarks - PCMarkPCMarkVersion and / or Patch Used: 2004Developer Homepage: http://www.futuremark.comProduct Homepage: http://www.futuremark.com/products/pcmark04/Buy It Here
DDR vs. DDR-2 - Benchmarks - 3DMark033DMark03Version and / or Patch Used: 340Developer Homepage: http://www.futuremark.comProduct Homepage: http://www.futuremark.com/products/3dmark03/Buy It Here
DDR vs. DDR-2 - Benchmarks - Halo PCHalo PCVersion and / or Patch Used: RetailDeveloper Homepage: http://www.bungie.netProduct Homepage: http://www.bungie.net/Games/HaloPC/Buy It Here
DDR vs. DDR-2 - Benchmarks - Unreal Tournament 2004Unreal Tournament 2004Version and / or Patch Used: 3323Developer Homepage: http://www.atari.comProduct Homepage: http://www.unrealtournament.com/ut2004/Buy It Here
DDR vs. DDR-2 - Final ThoughtsFinal ThoughtsDDR-2, like most new technology that is here to stay, is something that has to be proven over time. DDR so far has the upper hand, as its lower latencies and bandwidth matching performance shows that higher bandwidth in theory isn't always better, but to be frank it is hard to draw definite conclusions from this due to a number of factors.First we are dealing with first generation DDR-2 modules as well as first generation DDR-2 motherboard chipsets. DDR didn't fully blossom until the third and forth generation chipsets started to take advantage of this new technology, and they have had since 1999 to the present day to perfect this technology, and perfect it they have. Second we are dealing with only one platform that has a nature of starting out slow and building up, after all, Pentium 4 when it first came out wasn't any faster than the Pentium 3, but we can't say that today, with the performance of the P4 now being at the 4GHz doorstep we see that the architecture is developed into a usable source, which is what DDR-2 must do.We can only hope that the upcoming 1066FSB Pentium 4 and 925XE chipsets have better optimisations for DDR-2, as the extra bandwidth of DDR-2 at 533MHz is simply wasted, where it should be used for graphics card use or other high bandwidth systems, after all the P4 has its 6.5GB/s, the rest on the current 9xx chipset just wastes the remaining 2GB/s.
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