DDR, DDR2, GDDR, GDDR2, GDDR3

[Goi]

Hi,
Are there any articles that focus on the description and differences among these memory standards? I know the conceptual basics of a few of the(eg DDR2 has ODT and OCD for better signal quality and timing, and they all have different voltage signalling levels) but I'd like some more in-depth details, preferably with memory timing diagrams etc.

Thanks!

 

[dguy6789]

I am not too keen on the GDDRs, however I know the basic concept of DDR2.

DDR is frequencyx2, so if the chip is running at 200mhz internally, you would get 400mhz externally(PC3200 or DDR400).

DDR2 is frequencyx4, so if the chip is running at 100mhz internally, you would get 400mhz externally(PC2 3200 or DDR2 400). Technically, it is supposed to be 2x2 or something like that, but either way, it works out the same in the end.

If someone knows more on the subject, feel free to correct me.

 

[Goi]

After some googling, here is a good PDF about DDR2 technology and how it compares against regular SDRAM and DDR. I found a couple more that go into each of the features in even more depth, but I guess the majority of people don't really care that much, so this paper should suffice.

Still can't find much info about the GDDR types though.

 

[canadageek]

sdram sends one bit/clock cycle internal speed 133Mhz
DDR sends two 133Mhz internal becomes a 266Mhz "effective" speed
DDR2 sends four 133Mhz becomes 533Mhz effective

EDIT:

the latencies go up as you send more bits. so to compensate, higher clock speeds are needed. thats why AMD hasn't yet implemented DDR2. the higher latency would result in a performance loss, despite the increased bandwidth, which benefits the P4.

 

[Goi]

Yeah, those I know. I was hoping to find more detailed information, such as how the differential DQS signal on DDR memory runs(clock forwarding? what?) and how it's different on GDDR3 where it's no longer differential but unidirectional and split for reads and writes. Also, stuff like center-tap ODT in DDR2/GDDR2 vs ground to VDDQ for GDDR3, how exactly that works. That kinda detailed stuff.

 

[Witling]

Have you read Navigating the Memory Upgrade Jungle at TomsHardware? This article has more information on memory than I'm interested in and I haven't read it all. It also has additional links embedded. I realize that this isn't a direct answer to the question you asked but ithe article is about 25 pages.

 

[Goi]

Thanks. I haven't read that, but I will. I've read all the memory articles on Arstechnica, Aceshardware and LostCircuits though, and while they present some valuable information, some parts had me confused, and others weren't as complete and specific as I'd like them. At first glance, the THG article seems to be more concerned with actual memory modules on the market, rather than the theoretical features/differences between the various DDR standards, and it also seems to leave out the GDDR variants as well, but I'll look into the article in more detail anyway.

Thanks again.

 

[Nullvoid]

This link will probably suit you then:

Samsung article