After a rather lengthy radio silence, Mark Cerny, PlayStation 5 lead system architect, finally unveiled the key technical details of Sony’s upcoming gaming console.
At a presentation that was originally meant to be made at the Game Developers’ Conference before it was cancelled due to the coronavirus, Cerny spoke in detail about various aspects of the console’s underlying design philosophy and choices. The console is powered by an 8-core AMD Zen 2 CPU and a customised RDNA2-based GPU, the same basic technology as the Xbox Series X.
Where it differs from the Series X, however, is in the finer details of the design. Cerny stated that the design team opted for a higher-clocked, smaller GPU as opposed to a lower-clocked fatter GPU; Thus the RDNA 2 GPU in the PS5 ended up being a 36 CU GPU running at a cap of 2.23 GHz, compared to 52 CUs of the Xbox Series X running at 1.8 GHz. The CPU as well runs at a cap of 3.5 GHz, compared to the Series X’s 3.6-3.8 GHz clocks. The GPU also features ray-tracing support, as confirmed earlier by Sony during CES.
The GPU’s total raw compute power comes in at 10.3 Teraflops, which is about 1.8 Teraflops lower than the Xbox Series X, but Cerny insists that Teraflops is not the be-all of performance. "Performance is noticeably different, because 'teraflops' is defined as the computational capability of the vector ALU. That's just one part of the GPU, there are a lot of other units - and those other units all run faster when the GPU frequency is higher. At 33 per cent higher frequency, rasterisation goes 33 per cent faster, processing the command buffer goes that much faster, the L1 and L2 caches have that much higher bandwidth, and so on," Cerny explained in his presentation.
The PS5 also features interesting power management technology, brought about by use of a constant power, variable frequency design that the PS5 team opted for, rather than varying the power consumption based on load and keeping the clocks constant. The console uses AMD’s SmartShift technology, originally unveiled at CES 2020. Cerny says the console features specialised power management elements in the main chip, which allows developers to maintain a fine-grain control of where they want to put more power into.
This means the console’s CPU and GPU will not always run at the capped speeds, and will vary depending on available power and thermal budget. However, Cerny believes the console will run at the rated speeds, or close to it, most of the time because power and frequency do not operate on a linear curve. “When a worst case game arrives, it will run at a lower clock speed. But not too much lower, to reduce power by 10 per cent it only takes a couple of percent reduction in frequency, so I'd expect any downclocking to be pretty minor".
The key to the PS5, however, appears to be in the SSD and the sound technology. The PS5 team went for a very heavily cusotmised SSD design, which uses a bespoke design to deal with elements such as coherency, caching and I/O throughput.
| PlayStation 5 technical specifications | ||||
| CPU | 8 AMD Zen 2 cores at 3.5 GHz (variable frequency) | |||
| GPU | 36 CU custom RDNA2 at 2.23 GHz (variable frequency) | |||
| RAM | 16 GB GDDR6 at 256-bit. 448 GB/s bandwidth | |||
| Storage | 825 GB custom SSD, NVMe storage expansion | |||
| Expansion | USB Hard drive support | |||
| Optical drive | 4K UHD Blu-ray drive |
The design team went for an 825 GB proprietary SSD, coupled with a 12-channel interface hooked up to a custom flash controller, all linked to the main chip via 4 lanes of PCIe 4.0. This effectively provides 5.5 GB/s of raw bandwidth, which is about 100 times faster than the hard drive on the PS4. Sony is also providing an NVMe slot in which to add a PCIe 4.0 rated SSD, but details on compatibility were not made public.
The SSD also supports the new Kraken compression library, which is about 10 per cent more efficient than the ZLIB library on the PS4. This, Cerny says, results in an effective bandwidth of nearly 9 GB/s, which is way faster than any commercially available high-speed NVMe SSD on the market today. “In terms of performance, that custom decompressor equates to nine of our Zen 2 cores, that's what it would take to decompress the Kraken stream with a conventional CPU”, Cerny says with a hint of pride in his team.
The PS5 also sports a dedicated DMA controller which directs the data where it needs to go, and there are two dedicated processors that tackle I/O and memory management, alongside a coherency engine, which manages data in GPU cache, with fine-grain control of which memory addresses need to be evicted or overwritten, ensuring fewer operational cycles are wasted.
As for the audio, Sony went all-in on what the team believes is a severely under-represented part of gaming.
Cerny spoke about how the PS4’s Jaguar CPU just didn’t cut it for high-fidelity audio output, and it was a step down from the PS3’s Cell engine, where the SPUs proved ideal for audio processing and output. Therefore, the team created what they call the ‘Tempest engine’, which supports hundreds of sound sources.
The design philosophy of the Tempest engine is based around locality, and Sony went down the path of biological inspiration for it. Enter HRTF - Head-related Transfer Function. Sony mapped hundreds of peoples’ heads and ears physically to create a range of audio perception with the end goal of immersing people into the game completely, regardless of what they are using to output audio. The team also re-engineered one CU from the RDNA GPU to operate as an SPU by stripping it of its cache and working entirely on DMA transfers.
And while Sony aims to please every single person who will buy the PS5, it is not physically feasible to map everyone’s heads to get their ideal HRTF. "Maybe you'll be sending us a photo of your ear, and we'll use a neural network to pick the closest HRTF in our library.
Maybe you'll be sending us a video of your ears and your head, and we'll make a 3D model of them and synthesise the HRTF. Maybe you'll play an audio game to tune your HRTF, we'll be subtly changing it as you play, and home in on the HRTF that gives you the highest score, meaning that it matches you the best. This is a journey we'll all be taking together over the next few years.
Ultimately, we're committed to enabling everyone to experience that next level of realism,” Cerny explains.
While there is much more to be learned about the PS5, including its actual design, the controller and, of course, the games, Cerny says it will be revealed in due time – perhaps with a teardown (which generally comes closer to release of the console). At this time, the PS5 is still slated for release during the holiday 2020 season.