Talk:DDR SDRAM

Minimum speed?

All dynamic RAM has a minimum speed at which it must be clocked in order to retain data. I'd like to see minimum frequency figures for various DDR RAM types. This information is important when underclocking. And it determines whether newer RAM can be used in older systems.

edge

There needs to be an explanation of what is meant by an "edge" as in a clock edge. Preferably that explanation should go on its own page then be referred also from the page that talks about edge triggered interrupts, and the edge detection in image processing page

Vandalism

Looks like someone has been vandalizing this page. Can anyone revert a page, or must an administrator do so?

Anyone can do it, although admins can use a shortcut. Everyone else can just go to the edit history, open the last good version and then save it. I have fixed the vandalism you referred to. --Heron 21:34, 15 Jun 2005 (UTC)

"Rambus memory (RDRAM®) is a revolutionary step from SDRAM" Please NPOVify such statements. --Taw

It would be nice if someone would say whether DDR modules are backward compatible; ie if I can use DDR333 in a DDR266 motherboard. Thue

AFAIK, there are some speeds not listed: PC3500 (433 MHz), PC4000 (500 MHz), and PC4400 (550 MHz). --Ubern00b 19:34, 21 Sep 2004 (UTC)

I removed all speeds higher than DDR400, as none of these are JEDEC standards. They're simply overclocked DDR400. I removed mentions of quad-channel DDR, as I've never seen or heard of it used, if anyone has cites that would be great. I removed mention of QDR and Quad-Band as competitors, as neither ever materialized as products. Alereon 06:28, Nov 9, 2004 (UTC)

I have merged DDR RAM with this one and placed a redirect instead.

What about DDR2 RAM? It's worth a mention don't you think?

hi could someone please write an explanation on this page of pc2 chips? and if possible talk about the various chips found on ddr and their tolerance to overclocking perhaps ( the TCCD and UCCC chips) i would be grateful. thx.

Upgrading

1)When upgrading a computer that already has a memory stick by adding another stick, what considerations does one have to make? 2)Can you mix sticks with different latencies? 3)Can you mix single sided with double sided? 4)Can you mix different brands?

not sure when this question was asked but answers: 1) brands supported by your motherboard, size and speed supported by your BIOS 2) yes, most of the time 3) yes, sometimes. This is governed by your motherboard not the memory. Some motherboards allow dual-sided memory in only certain slots or not at all. This should be in your motherboard manual. 4) yes. no problems if #1 is followed through. 70.20.252.106 (talk) 18:56, 28 February 2008 (UTC)

Single-sided vs. dual-sided?

I vaguely understand that there are differences between single-sided vs. dual-sided DIMMS, am I correct? Can someone explain the differences?

Thanks. Penedo 05:11, 31 August 2006 (UTC)

Double sided, better called double-row, memory requires more organisation from the memory controller as it usually has more chips than single-sided, better called single-row, memory. 512MB sticks usually have 8 chips in single and 16 chips in dual, the memory controller has to adress all chips (less work to adress only 8 chips). Additional info: single/double refers to the internal organisation but not to the external mounting of the memory chips. It is possible to have have 8-chip (4 per side) sticks but internally single-sided (rowed).

Thanks for the explenation. Is there a definite way to find out from a chip's specification or the way it looks whether it's Double-row or Single-row? I raise the question because I was bitten by buying a double-row memory module which didn't work with my motherboard because, as it turned out, it supports only single-row (or maybe I hit the limit of rows that MoBo supports? I don't know. Someone on the net told me that maybe what counts for the MoBo (or the memory controller) is the total number of rows, no matter how many memory modules they are spread over). Penedo 07:04, 1 September 2006 (UTC)

I added explanation of this issue to the page under sections "Chip characteristics" and "Module characteristics". Hope it's intelligible and helpful. I had the same problem of identifying chips recently and didn't find info at Wiki, so here it is finally. As I state in the article one should not mix notions of number of rows (ranks) and number of sides, because they are not-so-tightly connected. Alexander Abramov 16:32, 13 October 2006 (UTC)

This "row" terminology for number of sides seems really unfortunate considering that each chip has rows (a different kind) and columns (and banks, I think). DHR 21:12, 19 November 2006 (UTC)

Is there anywhere that has a good explaination of how ddr and ddr 2 is accessed (IE, how does the northbridge exchange data between the two types of memory?) From my limited reading, I believe that the bus size in most computers is 64 bits, so data is transfered at 100 mhz but 4 bytes are transfered, or the same as transfering 1 eight bit word (byte) at 400 mhz. How is ddr two different, or is it truly just a faster transfer rate? I saw a intel presentation that seemed to show serial data transfer. Can someone point me in the right direction?

DDR uses both edges of the clock to perform transfers so a 100mhz clock gives 200 megatransfers per second. If each transfer is 4 bytes wide (which I belive it is with standard PC memory modules) that mean 800 megabytes per second.

DDR 533

does this version exist? or the top model is the ddr400? --83.190.159.64 18:47, 13 April 2007 (UTC)

Only as self-made specification by several OC memory manufacturers like Kingston, OCZ etc. Usually heavily overvolted standard memory. Not an official specification thus not in the overview. --Denniss 06:07, 14 April 2007 (UTC)

I think it should still be included—Preceding unsigned comment added by 66.194.72.10 (talk • contribs)

I tend to agree that it deserves a mention, properly noted that it's unofficial. Limiting the article to only the official versions edges on NPOV -- RoninBK _{T C} 20:03, 29 December 2007 (UTC)

We have this home-brewed stuff alredy as a small note in the article: Note: All above listed are specified by JEDEC as JESD79. All RAM speeds in-between or above these listed specifications are not standardized by JEDEC — most often they are simply manufacturer optimizations using higher-tolerance or overvolted chips.

If we start to include this non-standard then we soon have some IPs adding all the BS inbetween "designed" by all the different manufacturers. That's why we stick to the official, well documented, specifications. The same applies to the DDR2 and DDR3 articles. --Denniss (talk) 01:17, 30 December 2007 (UTC)

I did see that mention after the edit I made. It is awfully short and easily overlooked by someone, (ok myself,) looking to Wikipedia to figure out "What is this PC4000 stuff that this manufacturer is talking about?" I do understand the point you make, I'm just saying a one paragraph subsection, something like "Unofficial specifications", would be a welcome addition. -- RoninBK _{T C} 09:59, 31 December 2007 (UTC)

Chronology

Can we get some information about the years (circa) during which each type of RAM was typical? This would really help people trying to place older hardware in a historical context. Something like, "DDR1 ram was typically supported on motherboards sold from 199x to 200x" would be a very useful piece of information.

memory "DDR maximum capacity"

I read that the DDR memory maximum capacity is 1 Gigabyte por module. I think it should be checked and added to the entry if true. —Preceding unsigned comment added by 84.125.128.144 (talk) 13:45, 6 January 2008 (UTC)

DDR 300

Hi. I have re-added DDR 300 to the list, as another user deleted it, despite sources having been cited showing it exists. Does it belong in the article or not? Comments please. Thanks! --Rebroad (talk) 13:45, 2 March 2008 (UTC)

DDR-300 may exist but not as standard, that's only home-brewed stuff by some manufacturers. Have you ever read the small note below the table? Also i linked the recent JEDEC DDR-SDRAM specification (you may have missed this also as it specifically notes the cycle times). --Denniss (talk) 16:06, 2 March 2008 (UTC)

Ok, it exists but is not a JEDEC-standard. Therefore it needs to be mentioned, but the foot-note corrected, which I have now done. I don't know why you couldn't have done this yourself, rather than simply deleting it. --Rebroad (talk) 02:26, 4 March 2008 (UTC)

I have removed it again. If you want to list non-standardized "specifications" then search and list them all but under a different heading. If you continue to remove the link to the current JESD79E DDR-SDRAM standard it may be counted as vandalism or disruptive behaviour. IF you read this spec you won't find DDR-300 but, surprisingly, the cycle time you want to have a ref for. --Denniss (talk) 13:09, 4 March 2008 (UTC)

Denniss, if you have an issue with the heading, then change it. As it stands, I don't have an issue with it, as it is "specifications and standards", and DDR-300 HAS a specification, therefore it belongs. It is now mentioned that it is not part of the JEDEC standard, so I do not understand why you keep deleting it altogether. It is DDR SDRAM, is it not? Therefore whether JEDEC standard or not, it belongs in the article. I would understand your deletion if the article name was "JEDEC standard DDR SDRAM", but, it is not, so therefore, please explain your deletions. --Rebroad (talk) 09:46, 5 March 2008 (UTC)

Denniss, apologies, the deletion of the reference was accidental. Please remember WP:AGF. I am also assuming your deletions of the cn tags was also accidental (as per the timings section below). --Rebroad (talk) 09:49, 5 March 2008 (UTC)

Is DDR-300 listed in the JESD79 specification? No so it's no standard. As with those other ones like DDR-433 it's something home-brewed and far from any standardization. The same goes for PC-150 (SDR-SDRAM operation at 150 MHz just like your DDR-300 "standardd") - not a standard. --Denniss (talk) 15:33, 5 March 2008 (UTC)

Denniss, I don't know why you typed that. Did you read what I wrote above? --Rebroad (talk) 17:17, 6 March 2008 (UTC)

I'm not actively involved with this article and I don't want to get into a revert war over this apparently contentious issue. But if DDR300 is to be included in the chart, then all the other non-standard speeds should also be included. If that's the decision, then the JEDEC speeds should be clearly distinguished in the chart. As it stands, the special mention of DDR300 (at the exclusion of other nonstandard speeds) is confusing and potentially misleading about the nature of DDR300. It's nice that the non-JEDEC issue is mentioned in the small print, but the choice of items on the chart still doesn't make sense. -Greg 00:26, 30 Jul 2008 (UTC)

I've added a column in the chart for standard operating voltage of each speed grade. There is some variety of voltages on the labeling of different memory modules, especially with overclocked gamer ram, so it's useful to note what the standards are. There's an interesting change with DDR400, where JEDEC officially standardized a higher nominal voltage of 2.6v, while tightening the tolerances to only +/- 0.1v. This is indicated in JESD79E pg45. -Greg 00:43, 30 Jul 2008 (UTC)

Timings

Hi. Anyone know where the timing figures came from please? I couldn't find mention of them on the web, so I've added citation requests until a source can be found. These tags should not be removed until a reference is found and added to the article, otherwise the timings themselves can be deleted from the article if no sources are available, as wikipedia is not a place for original research, as per policy WP:NOR. --Rebroad (talk) 02:29, 4 March 2008 (UTC)

Dude, 10 ns = 1/(100 MHz).  ;-) 58.165.156.75 (talk) 12:19, 13 March 2008 (UTC)

It looks like Rebroad is not able or not willing to read the JEDEC specifiation as it clearly mentions the cycle time. BTW the DDR-300/PC-2400 is original research.--Denniss (talk) 20:01, 13 March 2008 (UTC)

Anyone know where the timing figures came from please? - yeah ... from math science ;)) Lothar25 (talk) 20:15, 30 March 2008 (UTC)

Production Period

Is DDR still in production? Checking market prices for 1 GB DIMMs it was March 2007 when DDR2 costed about as much as DDR ($60/GB street price). In March 2008 DIMM prices are about half ($30/GB), while DDR2 prices are about one quarter ($15/GB) - and the price drop for SO-DIMMs is much less than for DIMM ($50/GB), while the DDR2 prices for SO-DIMM are almost the same ($16/GB). Thus I wonder whether DDR2 is in mass production nowadays and DDR is out of production, but remaining stock only. --Traut (talk) 18:26, 18 March 2008 (UTC)

4 ranks for 1 DIMM?

From waht I know, there are no DDR1-DIMMs which have more than 2 ranks. I also know of no memory-controller, which supports more then 2 ranks per DDR1-DIMM. --MrBurns (talk) 03:31, 6 November 2008 (UTC)

Wrong picture top right?

It might be that the image shown top right is actually (I think 184 pinn) DIMM ram. I suspect, because DIMM has a little hole around the bottom center, while DDR ram has 2 holes (one around the bottom center and one around the bottom right). —Preceding unsigned comment added by 71.206.65.120 (talk) 22:19, 27 March 2009 (UTC)

prefixes

is the size of ram specified using normal SI prefixes or is it the convention to use the binary prefixes? I would suspect the last, but I'm not sure on this. if so It would be nice, and much more correct to use the correct binary prefixes MiB (mebibyte: 2^20) instead of MB (megabyte: 10^3) see:

• Mebibyte
• Nist
• IEC —Preceding unsigned comment added by 81.83.89.102 (talk) 10:39, 25 April 2009 (UTC)

History

Hi, can someone who knows add stuff about when it was first introduced, when it was widely adopted etc.? —Preceding unsigned comment added by 83.146.12.224 (talk) 19:37, 3 June 2009 (UTC)

What about adding a small section about RAMBUS litigation claiming DDR violates their patents? There's a small unclear section in RAMBUS entry mentioning DDR. —Preceding unsigned comment added by 99.235.238.24 (talk) 08:40, 14 June 2009 (UTC)

How is supply voltage controlled?

The article says weird things about the Vcc/Vdd supply voltage. SPD Byte 8 specifies the Voltage Interface Level; Byte 22 specifies some Vcc tolerances. How do 184-pin DDR SDRAM modules specify the Vcc supply voltage? It seems like the mainboards must be able to read something from the memory modules and know what voltage should be supplied. The article makes it sound sort of auto-magical, various voltages for various speeds. But when buying RAM, different modules at the same speeds spec different voltages (2.5V and 2.6V most common) -- it seems like there must be some hardware features that are supposed to make this all work together properly.

I would guess that some BIOS setup programs allow reading out the actual RAM voltage level, and doing a manual over-ride to change the supply voltage. It seems like the article should mention this aspect. -71.174.180.142 (talk) 21:16, 15 July 2009 (UTC)

This discussion:

• www.tomshardware.com/forum/111604-30-a7m266-memory-voltage-warning

says that some mainboards had jumpers that controlled the SDRAM supply voltage. -71.174.180.142 (talk) 21:28, 15 July 2009 (UTC)

Pinouts

This article is still quite skimpy, for such a core tech article!

We need some detailed pinout tables, or at least clear links to such info.

We need a picture of a standard laptop So-DIMM (200pin?)

We need a list/table of all the standard physical embodiments of DDR SDRAM, listing dimensions, number of pins, usage, etc -- ideally with a pic of each. -96.237.5.115 (talk) 12:54, 16 July 2009 (UTC)

JEDEC module standards

The article has links to JEDEC standards for chips. It says that there are also JEDEC standards for the DIMM modules. But what are the actual specific titles of those standards, and where are they?-96.237.5.115 (talk) 14:08, 16 July 2009 (UTC)

GB versus GiB

If i understand correctly, memory capacity is often expressed in GiB (gibibytes) while the symbol GB (gigabytes) is used. I felt Wikipedia would be the best place to start endorsing correct usage of these symbols. However, i'm not entirely sure the capacity of most memory is really 1 GiB or 1 GB. The way i see it, all "GB" and "MB" should be find/replaced into "GiB" and "MiB".