DDR-SDRAM: the memory of the future?
In March of this year, we publish an article analyzing the changes that there had supposed the appearance of the memory Rambus or "RDRAM" in the situation of the technology of memory for PC. Our conclusion was that his price, together with some technical considerations, they were doing a slightly advisable buy...
... And nine months later, it seems that we were not mistaken completely (which is a luck, he avoids us to have to eliminate this article about our web). At present it turns out to be very difficult to find PCs with memory Rambus, out of the exquisite ambience of the servants (where it is not the only present memory not much less either).
But the technology advances, and the veteran SDRAM, even in his version PC133, either it is not at a height of mikes which speed measures itself either in GHz. It imposes a change on itself, and it seems that the memory preferred by the manufacturers for this change is the DDR-SDRAM. Will it be on a par? Will it be worth it? Well, let's be fortune tellers again on this matter...
How is the DDR-SDRAM physically?
Or what is the same: can I install it in my "ancient" motherboard? Regrettably, the answer is a not round one.
The modules of memory DDR-SDRAM (or DDR, since we will call them from now on) are of the same size as the DIMM of SDRAM, but with more connectors: 184 pines instead of the 168 of the normal SDRAM.
Also, so that possible confusion does not exist at the time of installing them (which would have extremely unpleasant consequences), the DDR have 1 only notch instead of the 2 of the "classic" DIMM.
Obviously, it turns out to be a pity, but neither we can blame the manufacturers: the new pines are absolutely necessary to implement the system DDR, for not speaking that uses a different voltage and that, simply, would serve to us of nothing is able to install them, because we would need a new chipset not also.
Speaking about the voltage: at first it should be 2,5 V, a reduction of 30 % with regard to the current 3,3 V of the SDRAM. This will benefit very much the users of portable with memory DDR, which they will see developing his autonomy.
Since I console, let's think that the Rambus is not compatible with the badges for SDRAM either, and that really the SDRAM has lasted a few years, since the first DIMM of SDRAM interfered to 66 MHz...: and still turn out to be quite useful, what demons!
How does the DDR-SDRAM work?
Calm, that we do not think to enter terms as NOPs, bursts, you preload not even other technical trifles that, really, only the memoirs manufacturers are interested in and chipsets. The only thing that we are going to explain superficially the concept DDR is, that is to say, Doubly Byline Rate.
It turns out to be simple (of explaining, skylight): he consists of sending the information 2 times for every sign of clock, once in every end of the sign (the ascending one and the descending one), instead of sending information only in the ascending part of the sign.
Thus a device with technology DDR that works with a sign of "real" clock, "physical", of for example 100 MHz, will send so much information as other without technology DDR that works to 200 MHz. For it, the speeds of clock of the devices DDR usually happen in what we might call "effective or equivalent MHz" (in our example, 200 MHz, "100 MHz x 2").
And why does this do? Is not it easier to raise the number of MHz? Well, intellectually it is simpler, but it happens that the more rapid a device goes (in "physical" MHz), the more difficult it is of making. Precisely this is one of the problems of the memory Rambus: it works to 266 "physical" MHz or more, and turns out to be very difficult (and face) of making.
The technology DDR is fashionable lately, under this one or another name. In addition to the most numerous graphic cards with memory of video DDR-SDRAM, we have for example the microprocessors AMD Athlon and Duron, whose 200 MHz bus really is of "100 x 2", "100 MHz with double sign use"; or the AGP 2X ó 4X, with 66 well used "physical" MHz turn or cuádruplemente, since a graphic card with a bus of 266 "physical" MHz would be the most difficult to make... and extremely expensive.
(Attention, this does not mean that a card AGP 4X is in the reality the double of rapid that one 2X, not much less: sometimes they "are evident" EQUALLY of rapid, for motives that do not come to the case now).
Well, since the DDR-SDRAM is the concept DDR applied to the memory SDRAM. And the SDRAM is not different that our acquaintance PC66, PC100 and PC133, the memory that is used at present in almost the totality of the normal PCs; 133 MHz of the PC133 are already a level difficult to overcome without raising very much the prices, and for it the introduction of the DDR.