Slashdot Mirror
Is Rambus Destined to Return?
An anonymous reader pointed us to an article running over at Tom's that talks
about the world
of ram and criticizes the performance of DDR. The article goes
into DDR333, DDR400, and Rambus, and explains the issues at higher
clockspeeds.
Experience tells us that Rambus is faster.
Pocket books tell us that ddr is better.
Which will your wife let you decide on?
It seems to me that Rambus has offended so much of the industry that it even intel's continued (though lately lessening) support, or perhaps especially with intel's support it will fail to be implemented by the majority of m/b manufacturers.
Other avenues for gaining speed exist- like Nvidia's extra memory controller for the gpu in the xbox and higher end nForce chipset.
Intel had 2 reasons to bring out SDRAM based boxes:
1) Cost. Most consumers and business desktops don't care about speed, and RDRAM costs too much extra.
2) Speed. RDRAM looked fast because it was implemented with multiple banks. You can do the same thing with SDRAM, if you like. And that would give an apples to apples comparison.
Sorry...
Why is Grand Theft Auto a much more serious crime than Reckless Driving?
Seriously, ignoring pure performance considerations, RDRAM is garbage. It has to be put in pairs, and if those pairs aren't made by the same manufacturer, I've seen motherboards refuse to boot. Heat is a serious issue, and I've burned one finger too many on those heat spreaders. I've also seen an analog cable coming from the cdrom get stuck between the RIMM's and melt to the heat spreader. And price is still an issue, although it's improved quite a bit recently.
Expensive + Has to run in pairs + Runs very hot == Useless to me.
---- El diablo esta en mis pantalones! Mire, mire!
The fact is that most IC testers today support the lower-speed parallel connections. High-speed serial connections like Rambus and SERDES require very expensive mixed-signal testers with expensive and complicated load boards (the PCB between the tester itself and the chip). These high-speed serial I/Os on the memory ICs themselves are also generally much larger than on a DRAM, probably by a factor of 5. So, you don't get die savings, you don't get lower test costs, and most of all you don't have any processors whose front-side buses exploit this. Plus, you have very expensive target products in terms of motherboards to support the Rambus ram requiring tight trace routing and signal isolation, and their very limiting 28ohm max impedance (at least with the PC800 RDRAM), almost completely opposite in difficulty to DDR. So where's the advantage?
If you also figure that the memory controllers for Rambus are configured for dual-channel operation, it becomes much clearer that the advantage is not in the memory architecture itself but in the controllers. Suppose a server board manufacturer decides to support quad-channel PC2700 1GBx4. That's 10.8 GB/s of potential memory bandwith on sequential accesses! There's hope with chipsets like the Nvidia nForce420 dual-channel DDR, but the Athlon FSB is the limiting factor there. And let's not get into the infamous first-access latency issues which I hope they're finally addressing.
Rambus is also notorious for poor tech support. I worked for a major silicon vendor using their core, and they never responded to our requests for minimum PLL-to-Rambus core distances. It was abjectly ridiculous, but not surprising considering that regular SDR/DDR memory interfaces outnumbered Rambus designs 100:1. Have things changed? Considering what their legal bills have been lately and an erosion of their tech support, I doubt they can afford to improve it much.
on what systems you are working with? if you want a performance p4 system then obviously you use rambus... and if you want an amd system you use ddr(since there is no rambus/athlon chipset)
and until there is a rambus/athlon chipset i don't really think we can gague the real world implication of it...
either way i have better things to do with a few $100 than put it into a more expensive chipset/cpu/memory rig. if you have the extra money and the rambus system gives you what you want, then more power to you. overall, right now, you can't say either system is "the best" in ever possible catagory
I believe sex is highly over rated... unless it involves me
I think the point of that article is not that the Athlon is going to burn up.
There was a rumor being spread by some kids with AMD processors that the Pentium 4 runs at half speed whenever you do more than just checking email with your computer. They had taken a new feature in the Intel processor and manipulated it into a fault. Tom's article was only trying to explain what the feature is and why it's good, since many people did not understand what it was about. He was not in any way saying that your heatsinks are going to fall off and your processor will burn up, if you use an Athlon processor. It was not an attack on AMD, it was just an explaination of a new feature found in certain other processors.
Speed. RDRAM looked fast because it was implemented with multiple banks. You can do the same thing with SDRAM, if you like. And that would give an apples to apples comparison.
The whole advantage of RDRAM is high bandwidth/pin, and the fastest RDRAM has more than double bandwith/pin than the fastest DDR. RDRAM is very cheap to make dual channel because it has fewer pins. It is very expensive to make a dual channel DDR system because it requires that many more signals. The only dual channel DDR system I know of is the upcoming Serverworks Grand Champion chipset for the P4 Xeon which is very high-end (and no doubt expensive).
About a year or so ago, intel was doing demo's of Q3A at fry's to show off the new P4. Economy was good, I had like 4k from PTO that I aquired between jobs so I said what the hell and dropped $1500 on a 850dgb board, processor, case and 128 of ram.
I gotta say, this stuff is hot, my friends have all gone off and bought gforce3's, amd's with DDR. I thought these new cards/systems would have score winmarks well above my own (around 3800 with a gforce2gts) but I was surprised to see they only score 1000 or so more than me.
Out of curiosity, we put one of those GF3's in my system. Without fail I would score about 400 to come in around 6300 3dmarks above my buddies amd1.6. My P4 is just 1.4. Yet even with a lower clockrate the memory bandwidth made a huge difference.
I'm not trying to cause a ruckus here, anyone with deep enough pockets (or access to enough systems) can just as easily do the same testing I did. Bottom line whether or not the moderators like it is rambus systems do provide the absolute best possible performance in 3D gaming. It certainly was expensive when it came out but now with the falling prices of all ram, it's within reach of anyone that want's that extra "oomph" in thier system.
Does anyone know of any AMD boards that use rambus? I'm sorta curious what kind of scores those get in comparison to the intel one's. Anyways thats my comment.
It wasn't a bad article... I mean, the facts -do- show that the p4 runs better with RDRAM, and he addresses the consequences of that quite well, and quite neutrally. For that I commend him.
But he does misrepresent some issues. For example, signal integrity issues. I can say with complete assurance that Rambus is loaded with signal integrity issues. These issues get -very bad- as the clock frequency goes up. Also Rambus is -not-, strictly speaking, a serial bus. First, it is 16 bits wide, while pure serial would be 1. Second, the depiction of a DIMM as being a unterminated stub with significant SI issues is correct, but this doesn't go away with rambus, and this definition of "serial" fails as well. While the signals do pass through a RIMM continuously, eliminating the RIMM itself as the source of major SI problems, you still have each and every RDRAM device itself acting as an unterminated stub, each of which causes reflections of its own. Especially for devices with tolerances as low as RDRAM, this can be difficult to manage. While in the balance I'd have to concede that at a given clock frequency RDRAM has the SI advantage, remember that RDRAM needs 4x the clock frequency of DDR to match bandwidth.
Or you could have 2 channels of rambus, and only need 2x the frequency. Well, 2 channel DDR is becoming a reality. Not only does nForce support it, Sledgehammer will as well. Neither of these are Intel platforms, but I would guess that going dual-channel would be a natural step for VIA and others competing with Intel chipsets. It would especially make sense for p4, as it would more than make up the memory bandwidth disparity that currently exists.
Speaking of nForce, another thing I take issue with is the suggestion that the nforce's DIMM-slot population problems are indicative that DDR is crippled by SI issues. I think more likely is that this was the first chipset designed by a company whose experience lies solely with graphics cards, on which the ram is directly soddered to the PCB. Lack of experience in the harsher SI conditions of a computer motherboard are to blame.
Speaking of DIMM population, it's hard for me to see only having 2 DIMM's on some boards as a particularly black mark for DDR... That leaves you with 2GB per channel, the same as RAMBUS.
So, he was right about some things, insightful on others, but the picture is -not- so clear-cut in the image of rambus Inc.
The enemies of Democracy are
How is the parent post +4?
He links to an obsolete article from Q3 2000 about RDRAM on the Pentium III...
He talks about the "insanely high latency", and it's pretty obvious he's exaggerating slightly.
RDRAM's latency, particularly with the upcoming PC1066, is far better than people give it credit for. See this AcesHardware article.
PC1066 RDRAM latency for 128 bytes: 207 cycles
PC800 RDRAM latency for 128 bytes: 247 cycles
PC133 SDRAM latency for 128 bytes: 229 cycles
Slashdot moderators: Would it kill you to check the links before going points-crazy?
The days of cheap memory are over.
They say this because of the huge expense needed to provide 512MB or more of ultra fast memory. But what if they added yet another level of "cache"?
Put in 128MB or more of super-fast RAM (faster than today's RDRAM or DDRAM, maybe using an exotic bus) backed by gigs of cheap, easy-to-make memory (PC266 DDRAM or slower). The cheap ram is still orders of magnitude faster than a disk drive. Manage them with hardware that does page swapping similar to virtual memory.
You could get good system performance and lower overall cost.
Then the political aspect is ignored and he talks almost exclusively about technical issues about why Rambus might theoretically be better, and uses existing intel chipsets as evidence.
Hello? Answer the question, please? Has Intel ever come out with a non-crippled DDR chipset for the P4? How do Intel's DDR P4 chipsets compare to non-intel DDR P4 chipsets? (ARE there any non-intel P4 chipsets?)
How much of the problem is political, and how much of it is a real technical issue?
Um... How was that FUD?
It's true. If the heatsink falls off your Athlon it is toast. (note that just in the last week or so a board was released that supported the XP's thermal diode... but for all other boards/chips, you still get toast)
Tom isn't the genius a lot of people think he is (or that he'd want you to think), but that was not FUD.
The enemies of Democracy are
First, it looks to me like RDRAM is still about double the cost of SDRAM, according to Tom's Hardware's own price guide.
They have $93 for 512mb SDRAM and $175-250 for 512mb RDRAM.
My question is this: Let's say I have a choice between 512mb of SDRAM and 256mb of RDRAM. Would the SDRAM not almost always be faster because RAM, however slow, trumps swap space every time?
In other words, isn't the amount of memory I have more important than how fast it is?
Many moons ago, I had a SGI O2 workstation. Tremendous memory bandwidth, but memory that cost 10x more than anything else. As a result, it could be embarassed by lesser machines, since I couldn't afford to load it up with RAM.
I see Intel repeating the same mistake when it decided to focus on RDRAM.
Apple is putting L3 cache in their G4s so that the use of expensive RAM is confined to a relatively small and affordable amount. I can upgrade my PC133-equipped G4/450 dual processor to the latest 1ghz dual processor, put my 1.5gb RAM in it, and fly. That seems like a good compromise to me, maybe better than going to DDR, which I would have to buy new.
Thoughts?
D
I work for a test and measurement company and we sell logic analyzer tools for both DDR and RAMBUS. I service at least 1 site of each of the major computer manufactuers and I can tell you none of them are even considering RAMBUS. In fact, I can't remember the last time someone asked me about it. The only thing I have consulted customers on is the future of DDR. If anyone was interested in RAMBUS, I'd at least be hearing murmurs. Keep in mind I am only looking at computer manufactuers, not the 3rd party Asian motherboard manufactuers. Who knows what they are doing.
Historically RDRAM has been plagued by cost, which has deterred its adoption, but this isn't why average reader of Slashdot dislikes it. They might claim that they think it's technically inferior (PC600 and PC800 have more latency than SDRAM, but PC1066 and PC1200 RDRAM will likely be out within the next year), I think a large majority of hatred of RDRAM comes from Intel and Rambus's business practicates.
Intel and Rambus were hoping to strangle the market into adopting RDRAM in order to hurt Intel's competitors, and when this failed (RDRAM's prices lead people to adopt PC133 and then DDR), they attempted to obtain royalties or sue developers of alternative memory technologies for patent infringement of one form or another.