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Wlakiz on 22 February 2013
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firelink said:
Wlakiz said:
firelink said:
Sad thing is all of that RAM will go to waste.

GDDR RAM is designed to transfer large chunks of data like textures, frames, shaders, etc. This is why they are commonly used in video cards.

The thing no one tells you is that GDDR is awful when it comes to sequential R/W. This is why gaming PCs are built with GDDR for video cards and DDR for system memory. Your system memory has to swap around millions of variables constantly while running.

Go buy a cheap flash drive. It will do great transferring large files. Try transferring a large number of smaller files - the thread will lock up/slow down.

Nintendo and MS made the right choice with DDR3/eDRAM. You get the benefits of sequential R/W while getting a part of the benefit of high bandwidth. Using the right system RAM is essential today, when the way the OS works is just as important as the games.


... define 'awful' please.


Awful was the wrong word to use.

 

Let's look at this more in-depth. The PS4 comes with 8GB GDDR5. This RAM is unified, which means the entire system has to use it. That means RAM for the GPU and CPU functions must be split.

First we'll take away 2GB for the OS. That's an estimate, it might be a lot lower than that. That leaves us with a pool of 6GB of RAM. If we just divide it in half, that's 3GB for GPU and 3GB for CPU. I'd more than likely guess it will be 2GB for GPU and 4GB for CPU. That makes more sense from someone coming from a PC background.

That 2GB of RAM for the GPU is going to run fantastically. That much RAM allows for an enourmous framebuffer to be passed. However, the 4GB of RAM for the CPU is what has me worried.

GDDR has a lot of latency. Considering the PS4 is using a massive 8GB, there is no way that these chips are fitting on the SoC. Because of that, even more latency is going to be introduced.

It's not going to make or break the system, but things that rely on the transfer of large amounts of smaller data (like a million 1KB transfers or something), it is going to struggle more than DDR3 would.

Video game code has millions of lines of code, swapping different variables in an out of memory and pointing to and deleting pointers to different parts of memory.

Sony is trying to use RAM dedicated to graphics use (transferring few, larger chunks of data) for system use (transferring plenty, smaller chunks of data).

 

Here are some references:

http://www.overclock.net/t/855871/why-arent-there-sticks-of-ddr5-ram

http://www.techspot.com/community/topics/whats-the-difference-between-ddr3-memory-and-gddr5-memory.186408/ (post #3)

Well first your estimate... 2gb for OS? Thats allocating 25% phyiscal memory. They are not putting windows vista into the system. At worse, I would assume it takes 256mb for OS (thats more than double the amount they reserved for the PS3).

Next we look at the purpose of the PS4. It is a video game console.. what kind of data does it handle? Graphics, physics and game logic. GDDR5 excels at graphics and physics computation. Would having 'slower' memory access affect game logic? No. Unless someone plan to host a sql server or run sorting algorithims, you're not even going to notice the so called 'higher' latency.

This generation, Sony made sure memory won't be a bottle neck for the system.