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Introduction


How is the DDR-SDRAM physically?

How does the DDR-SDRAM work?

Types of DDR-SDRAM and nomenclature

Yield

Price of the DDR-SDRAM (and trade wars)

Chipsets for DDR-SDRAM

Conclusion

Released page
11/10/2000


Author:
Juan Herrerías Rey
 

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DDR-SDRAM: the memory of the future?


 

Types of DDR-SDRAM and nomenclature

Of course, there exists memory DDR of different classes, categories and prices. It could not be so simple...

The first thing, it can work to 100 or 133 MHz (again, "physicists"); something logical, since it is a question of SDRAM with DDR, and the SDRAM works to 66, 100 ó 133 MHz (certainly, DDR does not exist to 66 MHz). If we consider the "equivalent" MHz, we would be before memoirs of 200 ó 266 MHz.

In the first case it is capable of transmitting 1,6 GB/s (1600 MB/s), and in the second one 2,1 GB/s (2133 MB/s). At first they were known as PC200 and PC266, following the classification system for MHz used with the SDRAM...

... But Rambus came and he decided that his memoirs would be called PC600, PC700 and PC800, also according to the system of the MHz. Since this would do that they seemed much more rapid than the DDR (something that DOES NOT HAPPEN, because they work of a completely different form), they decided to be named according to his transference capacity in MB/s: PC1600 and PC2100 (PC2133 it is slightly commercial, evidently).

To do an idea to us, let's see a few bands for different memoirs: Bands of different memoirs (MB/s)

But eye, it does not finish here the thing: as with his "progenitora" the SDRAM, there exists an important one (and stranger) parameter that he says much of the quality about the memory DDR: the value of latency minimal CAS to which it can work for a given speed. To understand each other: the latency CAS is bad (it is a time of waiting, lost time), so minor all that is, is better the memory.

According to the JEDEC (we will speak already later about this organism), the DDR-SDRAM can have CAS = 2 ó CAS = 2,5 (being more rapid that of CAS = 2). It is possible that even CAS memoirs appear = 1,5 (that would be excellent but the most expensive) or CAS = 3 (that would be slightly advisable). Attainable speeds as the latency CAS of the DDR-SDRAM

Also, since one sees in the table of the right (seizure of the specification of the JEDEC), the memory qualified CAS = 2 can reach speeds major than the CAS = 2,5 (up to 143 MHz if  2 lowers of CAS = to CAS = 2,5)... some supreme importance for the overclocking.

As it happens with the normal SDRAM, it will be difficult that in the shop they allow him to choose the type of CAS of the memory (as it is said in Castile, "this there are lentils: if you want the captures, and if you do not leave them"), but if buy in Internet pay attention to this parameter.

 

Yield

We have just seen that the DDR-SDRAM offers so much band or more than the Rambus; nevertheless, the question of which is it more rapid in the real life is a little more complex than this.

Since at the moment of writing these lines still basic badges are not on the market for memory DDR, we depend on the scarce information that are in hands of the big changing rooms of hardware, like AnandTech or Tom's Hardware.

Thanks to them we can affirm that:

  1. on having used memory DDR, the yield increase is I half-close 5-15 % (perhaps 10 % of average);
  2. the memory DDR is lightly more rapid than the Rambus (with small changes as the used applications, of course).
Both are very good news, especially thinking that the DDR should cost less than the Rambus. And 5 % of increase is not small, an eye: it can be equivalent to approximately 100 more MHz of microprocessor (proper, but quite trustworthy calculation). Or is it that you believed that for doubling the speed of a component (the one that is, even the mike) doubles the yield?

 


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