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Rambus and DDR RAM writeup
jerkychew writes "Hannibal over at Ars Technica has written part 3 of his RAM guide,, this time focusing on the technical details of Rambus and DDR RAM. As always, a good (if compliacted)technical read. " If you're not scared of pin counts and parity, then this is a cool article.
I better patent the process by which air is drawn into the lungs before it is too late.
Forget about using Rambus with much higher clock rates or for very large memories. Of course, they could achieve some performance increase by shrinking the physical size of memory. But this is impossible when Rambus already runs very hot, so hot that not all chips can be "on" at once. Maybe in a decade or two when process dimensions will shrink by an order of magnitude or so!
Rambus proposes a double bank solution. Wait a minute, I thought that their original selling point was their 16 bit data path and the consequent low pin count. Wow, double banking means a 32 bit data path. I think that the Rambus engineers are doing the "double think" here. Why not just use a 64 bit wide data path like everybody else.
Oh, I forgot, it wouldn't be Rambus any more then.
Doesn't this only work in a single processor system?
1) This article was intended as humor. Obviously for a humor-impaired person such as yourself the subtlety of this fact must have escaped you.
2) While this article does offer more hot air than previous posts, I still believe it is very funny. Obviously there are technical problems in compressing hot air, and we're working on them, but I still believe it is better than the use of cold-air in the post-modern 3rd wave era of bullsh*tting.
3)AMD has nothing to do with this article. For that matter, neither does Rambus, DDR SDRAM, the pope, or my left over bag of doritos chips.
4) It would take far less time if you would just start seeing things my way.
5) This is where the reader stopped.
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(Note: This article has been reformatted to fit your screen, and editted for slashdot-PCness)
Rambus - Evil standard put out by Intel. It's bad, really bad. You should never buy it no matter what. Why? Because Intel is an evil bad corporation that made lots of money. Buy AMD instead.. they, uhh.. made less money! Alternatively, buy the chips and drill holes in them to let out the evil spirits before use.
SDRAM DDR - Horray! Our savior! This type of RAM has none of the evil problems Rambus has (which, for space, we are choosing not to reproduce said list of problems), and they're made by a bunch of l335 d00ds fighting the evil Intel empire. Nevermind that they're produced overseas in sweatshops like Nike shoes and the people on the assembly line deal with chemicals that could take the paint off your car in 5 seconds flat... they are l335!
Not sure on release time, probably fall/winter this year. But anyway, here is a preview to get you salivating. Unfortunately it is in Japanese, but there are plenty of pretty pictures and graphs. Or you can work through the rough translation. (If you are not using Mozilla, just ignore the XUL stuff it tries to download).
Q.
And in addition, Toshiba makes very little SDRAM and currently no DDR-SDRAM so agreeing to pay royalties on those two really doesn't affect them.
you'd see that i said it was broken, and it is
sorry foolio, you fail!
...dave
Think different? I'd be happy if most people would just think...
thus my link
i'm not karma whoring
...dave
Think different? I'd be happy if most people would just think...
You probably just tossed all your cookies. (Wait a minute, that didn't sound right....) Slashdot uses Cookies to save your username and password, then matches that to their database for all the rest of your dynamic pages. Your computer isn't saving cookies, or just got rid of the one /. is using.
Yeah, yeah, yeah.... So I spelled Rambus wrong, AND complicated, AND made a bajillion other grammatical errors.... :-)
I was all excited to see my posting on slashdot, until I read it and saw all the mistakes I made. Now I feel like a doofus
And, yes, I even used the preview button. Unfortunately, all I checked was the HTML formatting. Live and learn, I guess.
No need. Just login again and the cookie will be re-created.
Do not spread "09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0" over the internet, thank you.
Remember the article about Intel working on a serial protocol for displays, to replace AGP... and everything else they're trying to make serial...
While in theory it does reduce complexity, there is a cost, as this article points out. And when you get down to it, RDRAM fits exactly into this category of "serial protocol"... basically it's making it go four times as fast down a pipe four times as narrow! Now, while Intel may be having second thoughts about this (internally of course), it still seems like another one of the serial protocols they're trying to promote, for better or worse.
I just saw the connection and had to share it.
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Put down the crack pipe, please. You look at the freaking spec sheet. For a single RDRAM channel transfering a 64Byte cacheline, you have a transfer latency of 40ns. aka, any given transfer will occupy 40ns. So in order to saturate the link you need to be able to transfer a cas in 40 or less ns. Considering they don't make parts with this high of a CAS latency, you're pretty much wrong.
In fact, a single rambus channel has full CAS bandwidth down to a 16byte transfer size. After that you are limited by the CAS bandwidth.
This is actually a lot better than some of the proposals for DDR-II
How do you explain that SDRAM can't saturate more than 1/3 of the P4 bus, but RDRAM can? The benchmarks on real systems are today's systems, but systems about to come out (e.g. the P4) have busses much faster (3x-4x) than what is out now, and will need RDRAM to keep up. That's what RDRAM is needed for. Save your benchmarks until P4 comes out (the first system to actually take advantage of RDRAM).
I'd say that's because it isn't a review. It's a technical explination of why Rambus is the way it is. The explination serves to shed light on what sort of goals were in mind and what sacrifices were made to get there. Combined with the first two parts of the series, and the rest to come, it's more of a history book than an editorial.
Personally, I like seeing articles that are informative like this, without getting into a "which one is better" match. If people read them, and (gasp) learn from them, then they can be better informed to make their own opinion, rather than just "Rambus baaad! DDR goood!". I've made my decision (mainly though choosing the other chip), but it's interesting to read nonetheless.
See above. Thursday, the second part of the article comes out.
It's like Ars has been castrated. They didn't really make any commitments to talk about which they thought was better; The only time they really complimented RDRAM they said that it had better bandwidth than normal SDRAM but wouldn't mention DDR SDRAM at that point. They also said that RDRAM had some benefit or other, "But this has problems as we will discuss in our next installment."
What pansies. If you can't say what you feel, then you have lost your ability to report the news. Tell us what we need to know, don't give us the marketing data. We can get that from the company webpages.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
I am only going to start worrying if Rambus gets Micron or Samsung to pay royalties for DDR SDRAM. The rest are small potatoes.
Because I'm not aware of it. Alpha EV7, due out next year, will have a low-latency, very high bandwidth (12.8GB/sec) RDRAM implementation. The engineers designing that processor don't seem to be aware of the fundamental limitation that you claim.
I'm not claiming that RDRAM is the way to go for today's PC's and PC applications. Who cares how many milliseconds it takes to cut and paste in Word? I'm saying that today's high-end servers, and tomorrow's high-end workstations (and yes, eventually, your PC) are/will be severely bandwidth limited.
A processor with an integrated RDRAM controller will be able to have low access latency and extremely high bandwidth (keep in mind that you haven't seen a processor with an integrated RDRAM controller, yet, so the current benchmarks should be taken with a grain of salt). The next generation of processors will have to use RDRAM to compete, because there isn't currently a good high-bandwidth alternative that scales.
Would I want a PC with Rambus? No, not today and probably not for a few years. But servers and workstations are a different animal.
Yes, RDRAM transmits 16 bits at a time, but if you take 4 RDRAM channels, then you have 64 bits at a time, with 4x1.6GB/s=6.4GB/s of bandwidth, all with the same pin count as a system with a single 64 bit DDR-DRAM system (which will supply only around 2.1 GB/sec). Therefore, for the same pin count, RDRAM will give you 3 times as much bandwidth.
As for latency, Intel did a poor implementation in which the memory controller was in the chip-set, and communicated with the processor over a standard bus. A better idea is to do what Alpha is doing, and place the RDRAM controller on-chip, which reduces the latency signifigantly.
Asympotically, there is no comparison. Processors will get more and more bandwidth hungry, and RDRAM will always supply much more bandwidth than SDRAM for an equivalent pin count (because of the pipelined--optimized data path with synced clock). Latency will be corrected by better implementations (although it will never rival SDRAM). Latency to memory is not quite as important as everyone here would have you believe, and it will become less so as caches get larger and better.
You can easily saturate a RDRAM bus with a single processor if you are streaming data in (which is common in media happy applications).
While this article isn't perfect, it does give a good overview of the competing memory technologies, and doesn't cave to the predominant "Rambus sucks" slashdot mentality.
As I've said many times in the past, in the future, memory will look more and more like Rambus and less like DDR SRAM.
in a distributed shared memory machine--where cache coherence is maintained with directories and dedicated inter-processor links, not with a snooping bus. There's probably a way to make it work in a snooping bus SMP system, it would be difficult, though. Very good question, Ben.
the limitations are not that big a deal. Yes, RDRAM will always be worse than SDRAM latency-wise, but not so much so that performance is compromised. If it were, then Alpha wouldn't do it because they aren't beholden to any RAM standard, and they have no designs on 'controlling' the memory industry, which people claim is Intel's reason for backing Rambus.
a deal.
|C|o |m|p|a|q| sells 12,000 Processor EV68 machine to DOD
As I said in the conclusion, I'll be stepping back and forming some opinions closer to the end of the piece. And as jazzyfox has pointed out, the article is neither a review nor a performance comparison. It's a technical explanation of how two technologies work, their individual advantages, and their individual drawbacks. Whenever I make a comparison between the two, it's usually for didactic purposes and not necessarily so I can make a blanket call as to which one is "better."
/it/ better for other applications.
And as far as which one is "better" it all depends on the situation. (I say as much in my intro to the Rambus section.) Individual technologies are "better" or "worse" for _particular applications_. Depending on the constraints that you're operating under (cost, latency, bandwidth, availability, granularity, etc.) one solution will fit your needs better than another one.
Yeah, sometimes it's easy to make a clear call on which of two similar technologies is better for 99% of the applications out there, like if you're comparing FPM RAM to EDO RAM. But Rambus is complex enough and different enough from DDR SDRAM to where it's not always a black and white issue. Rambus has advantages that make it better for certain applications, and DDR DRAM has advantages that make
But again, there are no benchmarks in the article, nor will there be. There are plenty of places where you can find out how an RDRAM system configured a certain way stacks up against a similarly configured DDR DRAM system running a certain set of application benchmarks. I'd suggest you check out one of those to see which technology best suits your particular needs. If you're just curious about how it all works, though, I hope my article can be of some help to you.
Senior CPU Editor | Ars Technica | http://arstechnica.com/
DDr may be technically supperior to rambus but its dead out of the water. WHy then?
:-( ).
one word, PATENTS!
Rambus owns the intellectual property of virtually every syncronized ram chip in existance (including ddr)and also including a really scary patent on using a register to address memory!
I know you guys probably just read the previous story here about a guy who now claims that internet stock transactions are his own personal property and the last thing you want to hear are more greedy corporations and whining but they are a real problem.
The only reason sdram is still here is that rambus made it available cheaply now to show that there is competition to the fcc and also to highlight rambus as the next big thing. Rambus promissed no ddr ram chips in large qualitites would ever be introduced without big lawsuits.
I also read a news article on zdnet explaining that the p4 will be rambus only.
As the chip becomes standard expect ddr ram to slowly vanish and people will all forget about ddram since all the vendors like compusa and directwarehouse wont stock ddr because the demand will be too low (remember AMD hardly made a dent in intels armour. Many bussinesses only buy computers with intel chips).
As soon as the ddr is made in smaller and smaller quantities the price to manufacter will go up making it even more expensive then rambus (remember rambus will sue othe memory manufactors unless its priced much higher then rambus.
Company officals admitted they will try this tactic to wipe out ddr.
I believe sadly that amd's sledghammer will als be rambus only (correct if I am wrong guys. I would be happy if I was.). I thought I saw an article here on slashdot that amd finally gave in to rambus demands.
Its a shame supperior technology will be blocked again.
Remember to write to your politicians on patent abuse because its really hurting us.
you mean 'l337' don't you?
Pope
Freedom is Slavery! Ignorance is Strength! Monopolies offer Choice!
It doesn't mean much now, it's built for the future.
on ars (the ones at the bottom are broken and point to part III), so here they are :
part I
and
part II
these are really good, and very educational!
...dave
Think different? I'd be happy if most people would just think...
All the information I have read has pointed to the latency as a killing factor to RD-DRAM. While RD-RAM has faster access, it is only 16 bits at a time, which puts it with DDR-DRAM. If there is something that myself or others don't understand about RD-RAM which will make it better for future use could please allaberate more then just saying Rambus is actually a solid and viable memory technology? I have heard many techinical arguments against it. I am willing to hear arguments for it but I haven't heard any yet so if you have some please post them as I am more interested in the truth then in personal bias.
Molog
So Linus, what are we doing tonight?
So Linus, what are we going to do tonight?
The same thing we do every night Tux. Try to take over the world!
Compliacted? Shoulda used the preview button.
So there I was. Naked. In a refrigerator. With a potroast on my knees. Smokin a cigar. That's when it got REALLY weird.
I've read enough... I'm just waiting for DDR SDRAM mobos to come out! Anyone have any ideas on how soon VIA and ASUS will be bringing something to market?
Vote Naked 2000
A feeling of having made the same mistake before: Deja Foobar
The slashdot crowd refuses to acknowledge that Rambus is actually a solid and viable memory technology (that's just a couple years ahead of its time). We'd rather just rant and rant about DDR is great and Intel sucks and Rambus is a fascist organization, yadda yadda yadda. Pack up your reality and go home.
I think the biggest problem with DDR SDRAM is the lawsuits. According to this article: http://www.tech-report.com/news_reply.x/882,
... I get very angry at what Rambus is trying to do.
... but basically these lawsuits need to be cleared before companies will invest in mass production of these chips.
June 16: Toshiba signed agreements with Rambus, Inc to pay Rambus royalties on SDRAM and DDR RAM based products. This development has the potential to seriously shake up the memory market. Toshiba has just set a precedent, and basically sold out the rest of the world's memory manufacturers.
Basically, Rambus is making Toshiba pay huge $$$ to make and market DDR SDRAM. In that article, it states that the royalty rate is even higher than RDRAM. (which we all know is way overpriced!)
Later on in the month, The Register ran this article: http://www.theregister.co.uk/content/3/11576.html
This one is by Hitachi which is counter suing Rambus stating they have an unfair monopoly on memory. Now I'm no lawyer, but reading these articles
Taken from the register piece:
Hitachi admits that the '804 Patent was issued to Rambus on September 21, 1999, and is entitled "Synchronous Memory Device Having An Internal Register."
There's more legal stuff in there
:P
A follow up I found on The Register, so at least ALi and IWill are in the hunt, preview boards out early fall... sigh. Gonna be a long wait until Christmas, I guess.
Maybe I should just tighten the belt and go for the 1040MHz Alpha (w/DDR, AGPx2)
Vote Naked 2000
A feeling of having made the same mistake before: Deja Foobar
Here's the dirt:
Rambus is a member of the JEDEC, a committee of Semiconductor manufacturers which was created to help set standards for different types of chips. All the major manufacturers are JEDEC members, as well as other companies including Intel and Rambus.
One of the agreements to joining the JEDEC is that you must disclose all patents, finalized and pending, to the committee and you may not withhold such information, or use information gained in the JEDEC forums to file your own patents.
Rambus decided not to follow the agreement, and instead filed a patent during the SDRAM standard negotiations which would attempt to patent the exact implementation of SDRAM which was being written up. In the patent office, if your patent is not granted you can get extensions on it by modifying it. So what they did is continually string the patent along for several years, modifying it slightly so that as the SDRAM (and later DDR-SDRAM standard) was finalized, their patent looked exactly like what the standard was supposed to be.
Now the patent finally went through (god bless those morons in the patent office), and since everyone has implemented their RAM according to the standard, Rambus is suing them all for patent infringement.
However, there is very little chance they'll win. First, they violated the JEDEC agreement. Second, there is certainly prior art. Third, there was a decision back in '96 (I think) against Dell Computer when they patented something which was the result of "An Industry-wide Standardization effort" where the courts ruled that their patent was unenforceable. This is going to happen to Rambus, as well.
As for Hitachi and Toshiba backing down and paying license agreements there are specific reasons.
After the settlement, Hitachi sold their RAM division to NEC. They don't have to deal with the problem now, and since NEC is incorporating Hitachi's RAM infrastructure into their own, the licensing agreements probably mean jack now.
Toshiba, on the other hand, manufactures the RD-DRAM which is used in the PlayStation 2. They're making enormous amounts of money from this, and if they didn't agree to pay more licensing fees to Rambus, Rambus might pull their RD-DRAM license, thus forcing Sony to find someone else to manufacture the RAM.
Hope this has been informative...
"I want to get more into theory, because everything works in theory." -John Cash