Is 8gb of DDR5 equivalent in bandwidth to 12-16gb of DDR3?

[poohbear]

hey all, so simple question, given that the PS4 will have 8gb of DDR5, how much is the DDR3 equivalent in terms of performance? I read that DDR5 ha almost double the bandwidth of DDR3, so how much more would the PC equivalent have to be in terms size to equal it in performance? Just curious, hoping my 16gb will be good for next gen games!

 

[san.salvador]

Size does it not make faster at all. Just bigger.

 

[Sheep221]

There is no such a thing as DDR5 RAM, it's called GDDR5. And the size is separate parameter from performance.
The computer with 6 gigs of DDR2 RAM will be performing slower than the one with 3 gigs of DDR3. The low size of memory may affect performance related to swapping, not the actual RAM speed(because if the RAM is full the computer stores the RAM data on HDD which is like 50x slower). But if you have enough RAM for everything you do, having it more will not affect the performance either way at all.
It's something like you have a one car you drive to work everyday and when you buy another car, it wont make your first car run faster.

 

[2is]

The PS4 uses that memory pool for main memory and VRAM. PCs have a dedicated pool for each and our high end GPUs already come paired with GDDR5

 

[poohbear]

I see. So why didnt Sony go for the much cheaper DDR3 RAM? Why buy GDDR5 ram at all? For that matter why do Nvidia & AMD use GDDR5 for video cards in the first place?

 

[blastingcap]

I see. So why didnt Sony go for the much cheaper DDR3 RAM? Why buy GDDR5 ram at all? For that matter why do Nvidia & AMD use GDDR5 for video cards in the first place?

I'm guessing it's because of higher performance, and GDDR5 is going to be replaced a year after the PS4 gets released, which should help drive down prices on "old" GDDR5. http://www.nordichardware.com/Memory/gddr6-new-graphics-memory-coming-in-2014.html Consoles aren't updated very often, so you might as well cram some pretty good hardware in there by today's standards, because 2 years from now, it'll look ho-hum compared to typical PCs, and five years from now, it'll look weak compared to typical PCs.

 

[BFG10K]

I see. So why didnt Sony go for the much cheaper DDR3 RAM? Why buy GDDR5 ram at all? For that matter why do Nvidia & AMD use GDDR5 for video cards in the first place?

Because GDDR5 has much higher bandwidth.

 

[poohbear]

I dont get it, the posts went from saying there's no difference to it has higher bandwidth to "they might as well"(even though its a crap load more expensive than DDR3, they figured "we might as well??" Thats the worst business decision ever!).

So it IS better performence wise than DDR3?? If u know, please explain!

 

[blastingcap]

GDDR5 has much higher bandwidth than DDR3. Yes there is a cost difference but there is also a performance difference. In this day and age is it wise to use already-outdated tech on a product that may have to last 7 years? Especially when you're the first one out, and your rival (Microsoft) can one-up you because they are going second? I doubt there is a huge cost difference to go to GDDR5 as a percentage of the cost of the entire unit.

 

[Wall Street]

poohbear,

There are two uses for RAM, 1) system memory (attached to the CPU) and 2) graphics memory (on the GPU). The PS4 is somewhat different that a PC in that it has a unified pool for both similar to how the xBox 360 or a PC with integrated graphics/APU works.

System memory does not need to be fast. It is feeding at most four cores. However, system memory needs to be large to contain most of the program you are running to avoid swapping to disk. Test have show that processors benefit very little from more than the 20 GB/s that dual channel DDR3 offers. For example, look at the performance difference between first generations of i5 and i7 CPUs. Half of the Core i-series CPUs in the chart I linked to have 20 GB/s bandwidth and half have about 30 GB/s (tri-channel) and it is impossible to see any performance difference.

Graphics memory needs to be fast, but not usually as large. PCs have separate graphics memory on the graphics card. A GTX 660 has 144 GB/s of bandwidth (7 times that of the CPU) while a GTX 680 has 192 GB/s and Titan has 288 GB/s bandwidth. Performance scales well with additional bandwidth, assuming that card has enough shaders and render pipelines to fill the bandwidth.

For the PS4, there is one pool of memory that is allocated to both the system memory and the graphics memory - therefore it needs to be both fast and large. 8 GB is needed because it is a unified pool. While GPUs can get away with 2 GB RAM and systems with 4 - 8 GB of RAM, the unified pool acts as as both. Therefore, the system can allocate 2 GB to graphics and 6 GB to system memory for example. An advantage of this arrangement is that if a game only needs 1 GB graphics RAM it can allocate the rest back to the system, or vice versa if more graphics RAM is needed.

However, the PS4 RAM also needs to be fast because it needs to handle both the CPU and especially the GPU data needs. Therefore, the PS4 memory bandwidth is believed to be between an HD 7850 and HD 7870.

 

[HutchinsonJC]

hey all, so simple question, given that the PS4 will have 8GB of GDDR5, how much is the DDR3 equivalent in terms of performance?

Why are you trying to compare these two different things in the first place? And why do you think they have to have an equivalency point?

Your dedicated GPU has GDDR5 on it. Your computer has a dedicated graphics ram (GDDR5) and a dedicated main system ram (DDR3). On a console, more times than not, there's only one pool of RAM and it's shared for graphics and system.

The example you're trying to lead us down:
8GBs of GDDR5 hopefully is not better, or is very close to the performance of 16GBs of DDR3. This example being worded in this fashion due to your wanting to have at least matching performance on your machine as the console.

Sorry, but GDDR5 is still faster (no point crying about it, you have GDDR5 on your GPU).

For simplicity's sake, if your data set fits comfortably within 8GBs, then having 16GBs offers no performance advantage.

If your data set is too big to fit within 8GBs, then part of that data set will need to be written to a Hard Disk Drive or SSD. And every time something has to be written or recalled from the HDD or SSD, you will take a performance hit. That's where "more RAM is better" comes in.

More RAM doesn't automatically mean better. And if you can get faster RAM that's just big enough to suit your needs, you will see better performance than buying eleventy billion GBs of slower RAM that you'll never fill up.

Edit:

I should throw out there that this is only a basic explanation. Don't get mad at me when you buy 8GBs of 2400MHz RAM and then don't notice a difference compared to your 16GBs of 2133. It's not all so simple and you've got a long way to go to understanding it all.

 

[poohbear]

Actually i asked a very simple question, & got different contradictory answers. Look @ my system specs, i'm perfectly happy with my beast of a system, i just wanna undestand why Sony went with 8gb DDR5 instead of 16gb DDR3, if there's no performance diff then why go with the much more expensive 8gb DDR5?

Let me try again:

Bandwidth wise, what is the DDR3 equivalent (in size) of 8gb DDR5? Is that better phrased?

Not talking about speed/performance, i mean how much bandwidth is available to the cpu/gpu with 8gb DDR5 compared to 8gb of DDR3? If there is NO difference, why did they go with the more expensive DDR5? ie if the performance is the same, why even bother spending the extra cash on DDR5? If DDR5 the performance is NOT the same, how much bandwidth would DDR3 need to match thr bandwidth of 8gb of DDR5?

Read the rest of the posts in this thread before answering cause there are a few ppl contradicting themselves which makes things more confusing!

For example how can one say there is NO difference in performance between RAM, just size, but they STILL went ahead & got only 8gb of DDR5? Why not get 16gb of DDR3 instead of 8gb of DDR5? Surely 16gb of DDR3 is much cheaper than 8gb of DDR5?

 

[Wall Street]

8 GB of GDDR5 is a size and not a bandwidth, likewise, 16 GB DDR 3 is a size and not a bandwidth. If you have a dual channel Mobo it will have about 20 GB/s of bandwidth if you use DDR3 1600. It doesn't matter if you use 2 2GB sticks or 4 8 GB sticks, it is about 20 GB/s. The GTX 660 and GTX 680 each have 2 GB of GDDR5, but the GTX 680 has much more bandwidth.

It doesn't matter anyways because you are comparing system RAM to Graphics RAM. Your PC has DDR5, but it is only on the GPU where it is needed.

Sony went with 8 GB GDDR5 because they needed higher bandwidth - this RAM is going to feed a GPU. You system RAM uses DDR 3 because the bandwidth isn't needed for CPUs.

 

[poohbear]

Ok, for the PS4, wouldn't the cheaper 16gb of DDR3 be better in the long term than 8gb of DDR5? GPUs only use DDR5?

 

[Piotrsama]

Ok, for the PS4, wouldn't the cheaper 16gb of DDR3 be better in the long term than 8gb of DDR5? GPUs only use DDR5?

No, because the GPU chokes with DDR3.
And no, they can use other memory types.

 

[biostud]

Higher memory bandwidth = higher speed
Larger memory = more data stored in memory

High bandwidth is very important for graphics and having 8Gb available for all data is 16x times as much as on the PS3, so it will be more than enough for the lifetime of the PS4.

 

[dave_the_nerd]

To OP: No.

But 8GB of 128-bit GDDR5 is equivalent to 8GB of 256-bit GDDR3.

 

[Torn Mind]

Bandwidth and latency determine how fast your data go to and fro from RAM, not size

http://en.wikipedia.org/wiki/Memory_bandwidth#Computation

 

[poohbear]

Wow, thanks guys, that explains it perfectly then. Thats all i asking!

 

[HutchinsonJC]

Let me try again:

Bandwidth wise, what is the DDR3 equivalent (in size) of 8gb DDR5? Is that better phrased?

Not talking about speed/performance, i mean how much bandwidth is available to the cpu/gpu with 8gb DDR5 compared to 8gb of DDR3?

You want to talk about contradictions?

You're asking about a comparison, as if there was some equivalency point, that shouldn't even really be done: bandwidth vs size

And then you continue by saying that you're not talking about speed/performance when "Bandwidth" is pretty much exactly that.

You need to reread my previous post.

8GB is a size. 16GB is a size.

The only advantage of a bigger number here is IF your data set requires the bigger number. IF you think your intended project/applications will fit comfortably within 8GBs of RAM, then you don't need 16GBs.


DDR3 is a kind of RAM... GDDR5 is another kind of RAM. GDDR5 is a lot faster than DDR3. GDDR5 is the kind of RAM used on today's Graphics Cards... hence the G.

They are using 8GBs of RAM because they don't think they will have a use for more than 8, and they feel comfortable fitting game data or whatever the user will use the system for into 8GBs.

They are using GDDR5 because it's a graphics ram that offers a lot of bandwidth and a lot less latency. But they are not using a main system RAM and instead the 8GBs will be used for everything. Which is a lot of really fast RAM. Graphics require fast RAM, but today's most intense graphics don't really need more than 2 to 3 GBs of RAM at the resolutions the console will be playing at. Which means the other 5 to 6GBs is, for all intents and purposes, system RAM.

You could not run a console on 100GBs of DDR3 like you could on 8GBs of GDDR5. There's no real point in asking what the DDR3 equivalent is to 8GBs of GDDR5. You won't find one. DDR3 is too slow to do what GDDR5 does.

 

[dave_the_nerd]

There's no real point in asking what the DDR3 equivalent is to 8GBs of GDDR5.

I do agree there's no point, but, technically, the equivalent is 8GB of DDR3 running at twice the speed, with twice the bandwidth. Or 4x the bandwidth, or 4x the speed.

So, quad-channel DDR3-2133 would be about equivalent to the memory bandwidth of a Radeon 7750.

Using GDDR5 for everything allows the console maker to use off-the-shelf parts to get crazy bandwidth headroom for system stuff. It's pretty clever, IMO.

 

[cytg111]

Using GDDR5 for everything allows the console maker to use off-the-shelf parts to get crazy bandwidth headroom for system stuff. It's pretty clever, IMO.

- And for the cpu to manipulate graphics data directly, not going over pci bus, card interface etc.

 

[dave_the_nerd]

- And for the cpu to manipulate graphics data directly, not going over pci bus, card interface etc.

Hubba.

 

[Aikouka]

Poohbear, your question is too rudementary to answer. GDDR5 and DDR3 have other aspects to them than just capacity that would determine their overall bandwidth. For example, with GDDR5, you need to consider the size of the memory interface, and with DDR3, you need to consider the number of channels. Both memory types also have clock speeds.

 

[Wall Street]

- And for the cpu to manipulate graphics data directly, not going over pci bus, card interface etc.

And dynamically allocate between system and graphics RAM. I recall Bethesda saying it was really hard to port some of the Skyrim stuff to the PS3 because the XBox had a combined 512 MB RAM pool while the PS3 had separate CPU & GPU RAM pools even with the same 512 MB total. When they ran out of graphics RAM on the XBox they just allocated more to the GPU than the CPU (for example 320 MB GPU and 192 MB CPU) but the PS3 doesn't allow this and only could do 256 GPU and 256 CPU.

There is also likely a cost component of their reason. Having a single memory interface and a combined CPU/GPU on a single chip is very cost friendly vs. separate CPU and GPU chips and separate memory interfaces. For example, an APU is always cheaper than a similarly low end CPU with an HD5450.