Memory question, DDR5 vs DDR3?

[Krieger91]

Random question here:

I was looking at the PS4 specs and noticed that it will have 8GB of DDR5 memory. I know this memory is used on current GPU's, but why is our system memory only DDR3?

 

[Dangman]

You misread the specifications: The PS4 has 8GB of GDDR5 RAM, not DDR5 RAM. That's not the same as desktop RAM. We've had GDDR5 in our graphics cards since 2008.

In addition, despite the similar name, the technology for GDDR and DDR are fairly different and a direct comparison isn't exactly correct.

 

[Krieger91]

You misread the specifications: The PS4 has 8GB of GDDR5 RAM, not DDR5 RAM. That's not the same as desktop RAM. We've had GDDR5 in our graphics cards since 2008.

In addition, despite the similar name, the technology for GDDR and DDR are fairly different and a direct comparison isn't exactly correct.

I guess all these news sites are just repeating information. They list the specs as having "8GB of unified DDR5 RAM". No mention of GDDR, so I am lead to believe there is some kind of communication problem somewhere.

For example:

http://www.officialplaystationmagaz...confirmed-8-core-cpu-8gb-ddr5-ram-on-die-gpu/

 

[Dangman]

Yeah someone fucked up somewhere as these two sites clearly state GDDR5:
http://kotaku.com/5985769/the-ps4s-specs-in-brief
http://www.engadget.com/2013/02/20/sony-details-playstation-4-specs-8-core-amd-jaguar-cpu-8x-bl/

 

[Liger88]

I guess all these news sites are just repeating information. They list the specs as having "8GB of unified DDR5 RAM". No mention of GDDR, so I am lead to believe there is some kind of communication problem somewhere.

For example:

http://www.officialplaystationmagaz...confirmed-8-core-cpu-8gb-ddr5-ram-on-die-gpu/

Sloppy journalism at its finest. Hate when sites repeat small technical details incorrectly either intentionally or by accident and never bother to later do an editors fix.


GDDR has always just been a play on DDR, why they kept climbing with the numbers is beyond me. Probably has to do with the standardization process happening more quickly for GPU's than CPU's.

 

[Deleted member 222586]

You misread the specifications: The PS4 has 8GB of GDDR5 RAM, not DDR5 RAM. That's not the same as desktop RAM. We've had GDDR5 in our graphics cards since 2008.

In addition, despite the similar name, the technology for GDDR and DDR are fairly different and a direct comparison isn't exactly correct.

Not really. GDDR5 is simply DDR3 optimized for different purposes... which is why I have no idea how they will make it work on the PS4...

 

[Skripka]

Sloppy journalism at its finest. Hate when sites repeat small technical details incorrectly either intentionally or by accident and never bother to later do an editors fix.


GDDR has always just been a play on DDR, why they kept climbing with the numbers is beyond me. Probably has to do with the standardization process happening more quickly for GPU's than CPU's.

Not really. GDDR5 is simply DDR3 optimized for different purposes... which is why I have no idea how they will make it work on the PS4...

Wild thought...

If PS4 uses an APU with on (mother)board GDDR memory...and then also borrows from the system DDR3 RAM...and Sony supplied the sloppy factoids to make and spoon feed the "8GB DDR5" gobbldy-gook to outlets?

Wouldn't be the first time specs from a manufacturer were warped/distorted for PR.

 

[defaultluser]

Not really. GDDR5 is simply DDR3 optimized for different purposes... which is why I have no idea how they will make it work on the PS4...

By relying on the same multi-level cache architecture the desktop chips do?

GDDR5 has much higher latency than DDR3, but we are still talking about slow ram here. The Jaguar chips might have longer than normal cache misses, but the overall performance should be okay. They could just hack together a shared GDDR5 memory controller.

Another thought that I had recently: if the hardware between DDR3 and GDDR5 is so similar, is it possible they could reconfigure 64-bit banks on-the-fly, so that you could partition memory to work as GDDR5 or DDR3 mode in 2GB chunks? Probably not, but it would be cool if it were possible

 

[Krieger91]

By relying on the same multi-level cache architecture the desktop chips do?

GDDR5 has much higher latency than DDR3, but we are still talking about slow ram here. The Jaguar chips might have longer than normal cache misses, but the overall performance should be okay. They could just hack together a shared GDDR5 memory controller.

Another thought that I had recently: if the hardware between DDR3 and GDDR5 is so similar, is it possible they could reconfigure 64-bit banks on-the-fly, so that you could partition memory to work as GDDR5 or DDR3 mode in 2GB chunks? Probably not, but it would be cool if it were possible

I smell another CELL processor type of deal....

 

[Deleted member 222586]

By relying on the same multi-level cache architecture the desktop chips do?

GDDR5 has much higher latency than DDR3, but we are still talking about slow ram here. The Jaguar chips might have longer than normal cache misses, but the overall performance should be okay. They could just hack together a shared GDDR5 memory controller.

Another thought that I had recently: if the hardware between DDR3 and GDDR5 is so similar, is it possible they could reconfigure 64-bit banks on-the-fly, so that you could partition memory to work as GDDR5 or DDR3 mode in 2GB chunks? Probably not, but it would be cool if it were possible

For what I've read, GDDR5 is a type of memory that associates banks with cores. Which means that every core has some banks associated but can't access the others. In a gpu this makes total sense since you have a thousand mini-cores working in paralel... and they don't necessarily need other cores memory and thus why you can optimize it.

But, for such memory to run SHARED with a standard cpu..... that seems interesting.

Your thoughts about changing memory type on the fly seems interesting... but I have no idea how that could be done

 

[defaultluser]

For what I've read, GDDR5 is a type of memory that associates banks with cores. Which means that every core has some banks associated but can't access the others. In a gpu this makes total sense since you have a thousand mini-cores working in paralel... and they don't necessarily need other cores memory and thus why you can optimize it.

But, for such memory to run SHARED with a standard cpu..... that seems interesting.

Your thoughts about changing memory type on the fly seems interesting... but I have no idea how that could be done

It's only a fanciful thought, and is probably physically impossible. But it would be an outstanding innovation in the upcoming future where we have shared memory and the GPU needs bandwidth and the CPU needs low-latency. Mixed signaling of the same memory chips would be an an amazing breakthrough

On the subject of memory channels attached per-core, we already have this: it's called NUMA. It was introduced to the PC world with the Athlon 64 multi-socket systems (due to an independent memory controller on each CPU), and pervades on multi-socket servers to this very day.

Consumer CPUs have gotten around this by combining all cores onto a single die with an interconnect/arbitrator, but the lessons on how to make applications perform well on NUMA systems are not lost on modern server developers. It did cause performance hits on some programs, but there are ways to fix those hits.