PS4 For Dummies

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I’ve seen some confusion about the PS4 specs, lets see if we can get some order out of the chaos.

PS4Specs

These are the official specs released and as the small note at the bottom says, subject to change without notice.

The RAM Question

People have falsely claimed that the PS4 features 8GB of graphics RAM (video RAM, vRAM). I’ve seen the 8GB RAM compared to the new nVidia Titan card with 6GB.

This is an incorrect interpretation, the PS4 features 8GB of GDDR5 RAM which is a type of RAM used today in high-end video cards. It is however NOT the total available graphics memory for graphics processing. The 8GB GDDR5 RAM is shared with CPU operations (even though SONY was very careful to avoid the word “shared memory” in this context)

Example:

A typical gaming PC today has 4-8GB of DDR3 system RAM and additionally features vRAM on the graphics card itself. Typically this is 1-4GB  with current mid-high range GFX cards and the nVidia Titan at 6GB.

So a typical gaming PC can have 5-12GB of total RAM between CPU and GPU, the PS4 has 8GB.

Are higher numbers for the RAM-type better (DDR3 vs GDDR5)?

Yes and no, it depends on the system architecture as well as RAM-type.

DDR-type RAM is generally optimized for CPU operations and architecture, GDDR-type RAM is optimized for GPU (Graphics Processing). Were I to use GDDR5 RAM for CPU operations in a standard PC (hypothetically), I would notice increased latency. Were I to use DDR3 RAM for GPU, the same applies.

So a higher number behind the DDR (Double Data Range architecture) is not immediately indicative of “better”.

Benefits Of Shared RAM in the PS4 (speculation)

The benefit of shared RAM in the PS4 could be a wider flexibility and dynamic access to memory. For example, a game might not use a lot of CPU-bound RAM for general purpose operations like AI, this means that more RAM can be assigned to graphics processing and produce higher graphical fidelity (higher resolution textures). Or, vice versa, if the game is not very graphics-RAM intensive, the PS4 can allocate more RAM to CPU operations. Games could benefit from this massively as this isn’t possible with a standard PC, you either have just enough, or you have too much of something.

An RTS traditionally has lower memory requirements on the graphics side as the main focus is large scale engagement, but requires more memory when it comes to AI and keeping track of actors as well as things those actors do. On a mid-range PC we often experience “bottlenecking” in either CPU or GPU. A relatively popular example is Mount And Blade which uses primarily CPU power as well as system RAM but GPU and vRAM is relatively underutilized.

The PS4’s shared memory architecture could conceivably prevent such bottlenecks.

Concerns (speculation)

As noted before, GDDR5 RAM was never used in conjunction with a CPU architecture before and we don’t really know how this can or will impact performance. Standard components in PCs, and with it the x86-64 AMD chip in the PS4 are not made to handle DDR5 so we have no data on how this will work performance-wise.

DDR3 and GDDR5 are very different and some of the things are very technical like bus-type, bus-speed, clock, transfer bandwidth, etc, but we can’t expect that both CPU and GPU will be using the same configurations for these things. i.e. there might be a situation where the DDR5 was adapted primarily for GPU performance but will under-perform with CPU operations, or vice-versa.

There is a reason why PCs have dedicated components for CPU and GPU and why on-board video cards tend to suck badly.

CPU

There isn’t really much to say here except that the PS4 finally decided to use x86 architecture which is the current standard PC architecture. The PS3 in comparison uses cell processors that are not compatible with x86 system architecture, which leads to problems when porting games to the PC (or XBOX 360).

8 cores are good and they are not shared with the GPU which is also good, this makes the PS4 a bit of a beast when it comes to CPU power (compared to the current gen). Current gaming PCs often feature 4-6 cores (core i7, etc) but 8 core processors are available to the public at a price. CPUs are hard to compare as the amount of cores isn’t the only measure of their power. Parallel processing is good but clock speeds are important, as well as L(X) cache, buss-type and access times. We have no information about those, the Jaguar is not currently available for consumers.

Needless to say, current-gen games utilize little to none of that CPU power the PC boasts as most games are designed for the (now old) 360 and PS3.

Another curiosity is that CPU and GPU are integrated, they are an APU, which has its own problems.

GPU

We also unfortunately have no precise information about the GPU core and chip.

All we know is that it boasts 1.87 TFLOPS which would put it close to a AMD Radeon HD 7850 (1.7 TFLOPS) which is a higher-end GFX card available to the public. It’s a good card but already a year old (and will be 2 years old when the PS4 actually gets sold to consumers).

Compared to that, the Nvidia GeForce GTX 690 boasts 5.6 TFLOPS, close to 3x the processing power of the Radeon 7850.

Yet again, a direct comparison of GFX cards and GFX power is not really possible as it all depends on architecture. The Radeon 7850 comes with 2GB of vRAM stock for current PCs, but the PS4 can conceivably utilize a lot more. In comparison the GTS 690 comes with 4GB vRAM stock. The question is, even if we say that the PS4 would allocate 4GB at any given time, would the 1.87 TFLOPS be enough to actually process all this available data?

Looking at the stock cards I would say no. Just slapping more RAM onto something isn’t enough to make it better. If we look at the HIS Radeon HD 7850 4GB iPower IceQ Turbo, which has 4GB integrated RAM, we notice barely any improvement in performance (http://www.guru3d.com/articles_pages/his_radeon_7850_ipower_iceq_4gb_review,1.html). It’s a great card, don’t get me wrong, but it could bottleneck the system.

It’s a curious choice to feature this flexible an architecture with this powerful a CPU and shared vRAM if the GPU won’t be able to process it.

Final Speculation

In conclusion I think that the PS4 will realistically not assign more that 2GB to the GPU, leaving 6GB for CPU purposes. All those social and connectivity features take RAM as well, even with a dedicated chip handling the processing in the background. Not to mention that a large chunk of RAM will probably be used for the on-the-fly video recording feature that has been demonstrated.

Developers will need to take this into consideration when coding their games, they can’t just assume all the 8GB will be available to them at all times. On a PC we are relatively used to turning off unnecessary programs when we are gaming but a console can not expect the consumer to switch off his ustream because Killzone suddenly dropped 10FPS. If the feature set doesn’t work with “everything on max” it doesn’t work period.

Ultimately the enemy of all consoles is Moore’s Law. If processing power doubles every two years, your console is twice as shit two years from now (hyperbole).

Similarly the PS4, when it finally gets released at the end of 2013, will feature static technology that will already be obsolete. Let us all hope that the next-next-next gen development-cycle will be shorter than the 8 years of software-stagnation we have experienced.

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4 Responses to PS4 For Dummies

  1. Paul says:

    “In conclusion I think that the PS4 will realistically not assign more that 2GB to the GPU, leaving 6GB for CPU purposes”

    You have that backwards. The majority of the RAM will be used for textures, normal maps, displacement maps, vertices, bone matrices, and deferred rending buffers (these get huge with MSAA). Very little RAM is used by gameplay code and audio (due to streaming, efficient compression, procedural techniques). Physics and AI (nav meshes) can take up moderate amounts of RAM. The operating system will likely be light weight, for some reference the 360 playing an empty XNA game uses less than 92MB (420MB free). I would guess that the XNA libraries and C# CLR take up around 20MB, that would put the OS at about 70MB. I highly doubt that PS4 OS will take more than 200MB, with an additional 100MB for video sharing (15 frame buffer at 1080p ~ 90mb). I imagine most memory hungry games will use 4-6GB of RAM for the GPU and the rest for CPU only tasks (a 70/30 GPU-CPU split on the 360 is common, even on the PS3 textures are cached on the XDR then transferred to the GDDR3). This is somewhat simplified since the CPU is also used for rending tasks like alpha sorting, occlusion culling, ect. Also unified memory means there is no need for CPU->GPU write backs or redundancy thus a lot of memory bandwidth and space is saved.

    The main difference between GDDR5 and DDR3 is bandwidth and latency. GDDR5 being high bandwith and high latency, and DDR3 is low bandwidth and low latency. One of the reasons why IGPUs suck is because they are bandwidth starved using system memory. This can be seen from how IGPUs scale with memory speeds and multiple channels. The CPU using the GDDR5 will cause devs to take more care in avoiding cache misses just as they have done with 360.

    I would also argue that the CPU is the relatively disappointing component. Jaguar is the next generation version of Bobcat, which is a low power tablet/netbook CPU. I was hoping to see Kaveri in the PS4. Though the move to X86 is a big win, and will be good for PC gamers also.

    The GPU is a good as it gets for a ~$400 console. Comparing TFLOPs on a console to that of a PC graphics cards is not the best comparison since DirectX and OpenGL do not allow the devs low level access to the gpu like a console does (granted a 680 or 7970 will still smoke the PS4 GPU). The move to GCN is also a big win for PC gamers, since engines can finally be built for tessellation from the ground up. Tessellation allows for easy dynamic graphics scaling, hopefully this means that four years from now PC ports of console games will have a much easier time taking advantage of the more powerful hardware.

    The threat of Moore’s law causing these upcoming consoles to quickly fall out of date is somewhat blunted now. Graphics are at a point of rapidly diminishing returns, a move to ray tracing will be needed to make graphics a lot better (though there still is a lot of headroom for physics simulations e.g. hair, fabric, and fluids). Lithography nodes are getting longer in time and more competitive for access. The delay of 20nm and Apple’s move to TSCM is the reason why Nvidia’s Maxwell and AMD’s Sea Islands have been pushed back to 2014. Frequency gains have been dead/marginal for the last 8 years, so we generally get a root(2) gain in performance every 18 months now. This upcoming gen may very well last as long as the current one, though there will be some interesting pressures from the Steambox, tablets and phones, and laptops/desktops with good preforming IGPUs (and maybe Nintendo?).

    • tradamtm says:

      We now have concrete information, the PS4 will allow developers to use up to 5GB of the 8GB RAM for game purposes (http://www.eurogamer.net/articles/digitalfoundry-ps3-system-software-memory), which makes my old estimate pretty accurate.
      Thats close to 1/3rd of RAM being reserved for OS or internal applications the PS4 runs.

      If you are correct with a 30/70 split, this means 1.5GB for CPU and 3.5GB for GPU. Now I might be wrong but 1.5GB for CPU seems very low for next-gen games.

  2. Pingback: Technical Difficulties: PS4 Hardware followup RE: Forbes’ Erik Kain | liveware.problem

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