PlayStation 5 vs Xbox Series X - Deep Dive: Part 1 - CPU, SSD & Memory

A follow-up to last week's post with early impressions on the next-gen console specs. Now that the dust has settled and we have clarification on various matters, I can finally tackle the subject with a deep dive. Will include comparisons between the two next-gen consoles, but also PC and current-gen consoles. This is one is overly long, quite technical and pretty dry. I don't know if there's an audience for something like this on Hive Gaming (or Steem Gaming) but this is obviously something that deeply interests me.

But first, a refresher on the specs. Digital Foundry has put together a comprehensive table that covers everything we know about the two consoles.

First, the similarities. Both consoles use a custom AMD SoC with Zen 2 CPU cores and RDNA 2 GPU. Both consoles feature NVMe-class SSDs, 16 GB memory, HDMI 2.1, and a 4K UHD Blu-ray. It all sounds very similar, but actually, the two consoles have significant differences. Although the end performance will be closer between PS5 and XSX than PS4 Pro and X1X, fundamentally PS5 and XSX are farther apart.

CPU

As with all modern silicon-based devices, it all starts with the CPU. Both consoles feature an incredible leap forward from the ancient, anemic Jaguar CPUs. A very conservative estimate suggest a 4x increase, but once you account all the bottlenecks eliminated and a huge single-thread performance boost, it's closer to an order of magnitude in terms of real impact.

This is the area where the two consoles are closest, as mentioned in my early specs review. Both feature 8x Zen 2 cores with SMT enabled (so, 16 threads). The Xbox Series X runs at a fixed 3.6 GHz boost clock, while the PS5 runs a variable frequency with "up to" 3.5 GHz. Mark Cerny (PS5's chief architect) has said that the actual clocks are much closer than you'd expect, and it drops only in specific scenario. So, it's safe to assume an effective clock speed of 3.4-3.5 GHz for the PS5. I must say, it's a bit of a surprise to see a console with a variable frequency - after all, console are designed to hit very specific, predictable performance targets. I suppose it's a narrow range anyway, and the extra headroom can be used relatively predictably.

So, it's pretty much even, though XSX has one last trick up its sleeve. Game developers can choose to disable SMT and push up the clocks to 3.8 GHz. I doubt there are any game engines today that can actually scale up evenly to 16 threads, so I'd expect this will be a popular option at least in the early years of this generation, and of course, for cross-platform games. Remember, the current-gen consoles feature 8 Jaguar cores, so that's something developers are familiar with.

How does this compare to PC? Mighty impressively. The closest CPU to these on the market is the Ryzen 7 3700X. It definitely runs at higher clock speeds - closer to 4 GHz in the typical workload. It also likely features greater L3 cache. There's no confirmation on the cache spec for either PS5 or XSX, but judging by where the Ryzen APUs end up, it's fair to assume it'll be significantly lower than the 32 MB the Ryzen 7 ships with - likely 8 MB or 16 MB. This should not impact gaming performance too much, though. The consoles will reserve 1 core for background apps, but on the other hand, consoles will be more finely optimized. The end result is performance akin to a $250-$300 PC CPU today.

The end result is that next-gen games will be vastly more complex, with more larger, more detailed open worlds, sophisticated physics, new types of gameplay mechanics we have not yet seen, etc. Unlike the last gen, this one will fundamentally change how games are made beyond just prettier graphics.

SSD

Consoles have been stuck with achingly slow, mechanical hard drives forever. Or, spinning rust, as PC enthusiasts affectionately call them. Sequential reads are extremely slow, but it's the random reads and writes were the HDDs completely choke up. As a result of a hard drive's stringent limitations, game developers have been heavily limited to the amount of data can be streamed. Game worlds can only be so complex, the characters can only move slowly, etc.

Enter, super-fast SSDs. This is the one are where PlayStation 5 holds a commanding lead. It has a cutting-edge PCIe 4.0 SSD offering an blistering 5.5 GB/s of throughput. Yes, this is as fast as the fastest PC SSDs today. XSX opts for a more conservative 2.4 GB/s SSD, but this is still an exponential leap over the HDDs. It's not just about the raw throughput though - both consoles feature integrated SSD controllers that feature compression tech. So, theoretically, we're looking at an effective 8 GB/s for the PS5 and 5 GB/s for the XSX.

Like with the CPU upgrades, the SSDs will lead to far greater complexity of the world, increased traversal speed, but more excitingly, new gameplay mechanics and opportunities that are simply not possible today. For multi-platform games, I don't expect there to be any difference between the two consoles. However, some Sony first party titles may push the boundaries in ways not possible on the XSX. Think - greater complexity, higher resolution textures, etc, but perhaps not fundamentally different.

Load times will be cut down significantly, and there'll be other benefits like saving game states, so you can resume where you left off even if you haven't played the game for a while.

One major challenge is that the console makers have traded off speed for capacity. The XSX features 1 TB of SSD storage, while the PS5 has only 825 GB. Yes, that's lower than the PS4! Combine that with more complex games, and it's definitely a concern. Microsoft has opted for easy expandability using a proprietary port, while Sony will offer support for PC NVMe SSD. On paper, Sony's approach is a lot more user friendly, but on the other hand, only very select SSDs will be compatible, which will create some confusion. As for PC gaming, well, once these next-gen exclusive games really get going, you'll probably have to upgrade your SSD too. For the interim cross-gen games, any SSD should be fine, though HDDs will start being dropped from system requirements in a year or two.

Memory

Both consoles feature 16 GB GDDR6 RAM, but take different approaches to get there. Sony take a pretty simple, tried and tested approach. It mates all 16 GB to a 256-bit unified bus, leading to a memory bandwidth of 448 GB/s. This is shared across the CPU and GPU. While Sony haven't announced the allocation, we can expect roughly 13 GB to be dedicated to games, with the remaining partitioned off to the system.

Since Microsoft opted for a larger GPU, 448 GB/s was simply not going to be enough bandwidth. At the same time, going for a 384-bit bus would have been too expensive. So, they came up with a clever solution by splitting the 16 GB into two pools. The faster pool features 10 GB at 560 GB/s. This is enough bandwidth for XSX's larger GPU. Meanwhile, the remaining 6 GB runs across a smaller bus, offering 336 GB/s. Developers can utilize all 10 GB for GPU related assets, while 3 GB of the slower pool can be used for CPU-related or bandwidth unconstrained data. The remaining 3 GB will be used by the system.

There's definitely some concern that the XSX's novel approach will lead to quite a few headaches for the game developers, but in practice, it should be relatively straightforward using the platform's development tools. After all, on PC, we have memory split between the CPU and GPU anyway.

While 16 GB by itself sounds like a pretty mild upgrade from the 8 GB featured in OG consoles - let alone the 12 GB in X1X - there's a different context in play here. It's all about the faster SSD.

With the older HDDs, games needed to load at least 30 seconds worth of gameplay's data on to the RAM, as it was simply too slow to swap out data any faster. With the new SSD's the RAM only needs to hold 1 to 2 seconds' worth. This is another exponential leap, and while the 16 GB number doesn't sound very impressive, the end result could be an order of magnitude more detail in your worlds and textures.

This is perhaps the only area where PC gamers will remain unimpressed - we have had 8 GB GPUs and 16 GB system RAM for years now, and fast SSDs to cache from.

Coming in Part 2: The GPU, a comparison with PC gaming, and looking ahead.