Why's XDRAM so slow?

[Shifty Geezer]

Press releases isn't proof it happened years ago.

RSX is basically a PC chip bolted on at the last minute.

Last minute being over 12 months before the console is released? In case you hadn't noticed, PS3 isn't out yet, and RSX hasn't been finalized. It's supposedly gonna be finished end of this year. This isn't six weeks before launch, Sony grabbing a GPU from a shelf to replace their part. This is a decision long before the console is released giving them time to work with the hardware and design it to fit in with their price/performance objectives.

Sure they may have made compromises where things haven't panned out as expected, but where you get this 'off the shelf bolted-on component' idea from...well, we all know where it comes from.

 

[Mulciber]

well, one thing we know they added was a flexio interface to communicate with the cell processor.

 

[PC-Engine]

Press releases isn't proof it happened years ago.

RSX is basically a PC chip bolted on at the last minute.

Last minute being over 12 months before the console is released? In case you hadn't noticed, PS3 isn't out yet, and RSX hasn't been finalized. It's supposedly gonna be finished end of this year. This isn't six weeks before launch, Sony grabbing a GPU from a shelf to replace their part. This is a decision long before the console is released giving them time to work with the hardware and design it to fit in with their price/performance objectives.

Sure they may have made compromises where things haven't panned out as expected, but where you get this 'off the shelf bolted-on component' idea from...well, we all know where it comes from.

AFAIK RSX has already taped out.

well, one thing we know they added was a flexio interface to communicate with the cell processor.

Well of course they would need to do this, otherwise it wouldn't work at all.

 

[Geeforcer]

I think RSX is going to be along the lines of NV2A - a customized solution heavily derived from existing PC products.

 

[London Geezer]

The point is, even if it's a bolt-on last minute job, ultimately, if this last minute change is faster than what was there before, who freaking cares!!! Some people will never stop nagging.

 

[Geeforcer]

Because fully custom design by ATI with embedded RAM is inherently superior to PC-derived Nvidia chip. Just look at how GC was 17.9 times more powerful then Xbox.

 

[ShootMyMonkey]

Because fully custom design by ATI with embedded RAM is inherently superior to PC-derived Nvidia chip. Just look at how GC was 17.9 times more powerful then Xbox.

Are we talking about a Beowulf cluster of Gamecubes here?

Seriously, if you listened to the old nVidia conference call around the time when Sony first announced they were going with nVidia for the GPU, they pretty clearly said that the agreement worked out such that nVidia would develop an IP for a GPU design, customized to work well with the CELL CPU (whatever that means), and Sony would "take the design and run with it."

It was more than certain that Sony evaluated a number of various potential providers for GPUs including themselves. Ultimately, it came down to nVidia -- and in some ways it makes sense considering that utilizing nVidia's parts wouldn't be all too unfamiliar to developers as opposed to another foreign GPU like the GS.

Personally, I happen to think NUMA was not a change of plans at all. At one point, the goal of putting multiple CELLs in the box was there (albeit with doubts as to whether it was possible) -- If such a thing were to happen, I would anyway expect the separate CELLs to have separate memory controllers. That's the most obvious path when putting a memory controller on the CPU die *cough*think Athlon64*cough*.

 

[Geeforcer]

Are we talking about a Beowulf cluster of Gamecubes here?

Sarcasm, my friend, sarcasm. Doesn't mix well with the internet and all that.

 

[London Geezer]

Because fully custom design by ATI with embedded RAM is inherently superior to PC-derived Nvidia chip. Just look at how GC was 17.9 times more powerful then Xbox.

Are we talking about a Beowulf cluster of Gamecubes here?

Seriously, if you listened to the old nVidia conference call around the time when Sony first announced they were going with nVidia for the GPU, they pretty clearly said that the agreement worked out such that nVidia would develop an IP for a GPU design, customized to work well with the CELL CPU (whatever that means), and Sony would "take the design and run with it."

It was more than certain that Sony evaluated a number of various potential providers for GPUs including themselves. Ultimately, it came down to nVidia -- and in some ways it makes sense considering that utilizing nVidia's parts wouldn't be all too unfamiliar to developers as opposed to another foreign GPU like the GS.

Personally, I happen to think NUMA was not a change of plans at all. At one point, the goal of putting multiple CELLs in the box was there (albeit with doubts as to whether it was possible) -- If such a thing were to happen, I would anyway expect the separate CELLs to have separate memory controllers. That's the most obvious path when putting a memory controller on the CPU die *cough*think Athlon64*cough*.

He was being sarcastic, and it made me laugh a lot actually.

 

[PC-Engine]

Because fully custom design by ATI with embedded RAM is inherently superior to PC-derived Nvidia chip. Just look at how GC was 17.9 times more powerful then Xbox.

RE4...24MB RAM...$200.

 

[mckmas8808]

So what is this all about.

Samsung said it has produced its first production samples of the multimedia-focused XDR DRAM, based on Rambus??? XDR memory interface technology, which can transmit data at a rate of up to 9.6Gbits/sec., reportedly 12 times faster than DDR400 memory and six times faster than leading RDRAM (PC 800) devices.

The memory device is aimed at broadband applications that need advanced digital imaging or 3D graphics, such as the latest game consoles, digital TVs, high-end servers and premium workstations, and uses 90nm memory technology to achieve a peak operating speed of 4.8Gbits/sec. at 1.8 volts, the company also said.

Source http://www.reed-electronics.com/electronicnews/article/CA602316.html?industryid=21365
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Ford 335 Engine History

 

[Shifty Geezer]

That's kinda the point. XDRAM is supposed to be fast, but it isn't in PS3.

 

[Vaan]

That's kinda the point. XDRAM is supposed to be fast, but it isn't in PS3.

Is fast as hell, but the bus is not wide enough to make an impressing bandwidth.

RSX-Cell-XDR must have RIDICULOUS latencies, but people tends to determine memory speed just with the bandwidth, not thinking of the much more less time to wait data to arrive, even when in a second arrives the same amount.

If i'm wrong, make me know.

 

[Panajev2001a]

That's kinda the point. XDRAM is supposed to be fast, but it isn't in PS3.

Is fast as hell, but the bus is not wide enough to make an impressing bandwidth.

RSX-Cell-XDR must have RIDICULOUS latencies, but people tends to determine memory speed just with the bandwidth, not thinking of the much more less time to wait data to arrive, even when in a second arrives the same amount.

If i'm wrong, make me know.

Two devices, embedded Memory Controller... come on, even Direct RDRAM on PlayStation 2 was not that slow (it was actually pretty speedy latency wise, compared to what PC main RAM could do at the time anyways) and XDR is a better memory technology than Direct RDRAM.

 

[Shifty Geezer]

I think Vaan is saying XDR has ridiculously LOW latencies, but people overlook this and only look at bandwidth, which is a point as has been raised. XDR is needed to keep the SPE's happy. I still don't understand why 3 GHz memory of a faster design is only about as fast as 700 MHz DDR, mostly 'coz the thread got derailed. But on this note, what are the comparative latencies between the XDR and DDR that PS3 uses?

 

[PC-Engine]

I still don't understand why 3 GHz memory of a faster design is only about as fast as 700 MHz DDR, mostly 'coz the thread got derailed.

...because comparing clock speeds doesn't show you the whole picture?

 

[Vaan]

That's kinda the point. XDRAM is supposed to be fast, but it isn't in PS3.

Is fast as hell, but the bus is not wide enough to make an impressing bandwidth.

RSX-Cell-XDR must have RIDICULOUS latencies, but people tends to determine memory speed just with the bandwidth, not thinking of the much more less time to wait data to arrive, even when in a second arrives the same amount.

If i'm wrong, make me know.

Two devices, embedded Memory Controller... come on, even Direct RDRAM on PlayStation 2 was not that slow (it was actually pretty speedy latency wise, compared to what PC main RAM could do at the time anyways) and XDR is a better memory technology than Direct RDRAM.

Whith ridiculous I mean very low Sorry if we have "lost in translation"

 

[archie4oz]

I think Vaan is saying XDR has ridiculously LOW latencies, but people overlook this and only look at bandwidth, which is a point as has been raised. XDR is needed to keep the SPE's happy. I still don't understand why 3 GHz memory of a faster design is only about as fast as 700 MHz DDR, mostly 'coz the thread got derailed. But on this note, what are the comparative latencies between the XDR and DDR that PS3 uses?

GDDR is a parallel memory architecture. XDR like it's previous Rambus brethren serialize memory tranfer in order to achieve higher clock speeds. Some benefits are (as already mentioned) low latency (mainly from a high clocked CPU's point of view), and more granular memory accesses.

 

[mckmas8808]

Samsung Electronics Co., Ltd., the world leader in advanced memory technology, today announced that it has produced the first 90-nanometer production samples of 512-Megabit XDR??? (eXtreme Data Rate) DRAM, the fastest memory for multimedia applications.

The Samsung 512Mb XDR DRAM can transmit data with up to 9.6 GigaBytes per second, 12 times faster than DDR400 memory and 6 times faster than leading RDRAM?? (PC 800) devices. It uses advanced 90-nanometer memory technology to achieve a peak operating speed of 4.8Gbps at 1.8 volts.

The memory device targets high-performance broadband applications that need advanced digital imaging or 3D graphics, such as the latest game consoles, digital TVs, high-end servers and premium workstations.

XDR DRAM from Samsung will be adopted for Sony Computer Entertainment???s next generation computer entertainment system, PLAYSTATION??3.
Yeong Ho Kang, Vice President, Memory Marketing, Samsung Semiconductor, said, ???We have worked closely with Sony Computer Entertainment to assure that the next generation computer entertainment system had what Sony Computer Entertainment wanted for the launch of PLAYSTATION 3: the fastest system memory with optimal thermal performance.???

Samsung???s XDR DRAM is based on Rambus??? (NASDAQ:RMBS) XDR memory interface technology. It can support the widest variety of data input and output requirements and will be available in x2, x4, x8 and x16 versions.

According to IDC, a market research firm, the XDR DRAM market will grow steadily over the next four years (2006-2009) to reach 800 million units of 256Mb-equivalent memory.

So this is going to be in the PS3.
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Strawberry cough

 

[Shifty Geezer]

No. We already have the specs for PS3's RAM. The XDR runs at something like 25 GB/s.