[Windows] Implement native unified memory architecture

A few months ago, Microsoft hinted that they wants to merge Xbox and PC together. Xbox consoles have used unified memory architecture since 2005, so Microsoft must release a PC with unified memory if they want support backward compatibility with those games. Backward compatibility will be a deciding factor for the success or total failure of the Xbox-PC initiative. Millions of people have collected hundreds of games over the past 20 years since Microsoft opened its own digital store But what exactly is an unified memory and why it is used by game consoles and Apple Mac M-Series computers? Basically in classic PC memory architecture the CPU and GPU can't work together efficiently. Both computation units use separate memory which is very slow and waste memory. For example, when the GPU computes something the CPU doesn’t see those results until you copy the changed video memory back to system memory. This is so slow that basically the CPU and GPU can't work together efficiently. All these problems are solved by unified memory where both processing units can access the same shared data. You don’t need copy objects into different memory pools. Both CPU and GPU can work together at full speed and you save a lot of memory Unified memory architecture is not only simpler but also cheaper because GDDR memory is soldered onto the motherboard. Hardware companies can buy millions of memory chips directly from the factory without any middleman companies. Using classic DDR5 is more complex because you need to work with external partners that build SIMM memory modules. Of course GDDR memory is also faster. For example, an Xbox Series X APU has 560 GB/s of memory bandwidth which is 5x faster than DDR5-6400 on dual-channel configuration (102 GB/s). A PC with GDDR7 memory and a layout identical to the Xbox Series X would have more than 1 TB/s of bandwidth. How could those next-generation Xbox-PC computers look? We can assume they will be very similar to the current Xbox Series X and still use 320-bit memory layout with 10 memory chips. This means MS will be able to use between 20-30 GB GDDR7 because currently only 2 GB and 3 GB chips are manufactured. For Xbox backward compatibility we need only 16 GB but the problem starts when you want to launch PC games. Existing PC games require two memory partitions: system and video. So Microsoft would need to divide the available memory into two partitions to simulate a classic PC memory layout every time when someone want to launch legacy PC game. So we need at least 28 GB to create those partitions as 16 GB system and 12 GB video which is necessary for 4K games on PC. So the best option will be a PC with 30 GB GDDR7. Hardware like this will be able to play both PC and Xbox games without any problem. **Adding unified memory to Windows PCs this will have a much bigger impact than a single device. It would be possible to create console-like optimizations on PC. Every APU will be able to use memory more efficiently than is possible today**. We will see a lot of notebooks and mini-PCs with really fast APUs using unified GDDR memory. We can assume that Asus, MSI, Lenovo and others will flood the market with multiple Windows based Steam Machine clones just like they did with a handhelds. If the Xbox-PC initiative will be successful we could even classic PCs adopting this pattern. How? Graphics cards already use processing unit using GDDR memory so all you need to to add CPU chiplet on it to essentially create a GPU with APU. This would convert a standard graphics card into a self-contained fully functional PC with unified memory. Card like this could be installed into any PC as easily as replacing GPU. Your main CPU and memory installed on the motherboard would be used only for system and I/O while games would run on the APU on your GPU card. **Of course, we don’t know if the Xbox–PC initiative is real. There have been many leaks in recent months but Microsoft has never confirmed it officially**. So my vision of PC with native support for Xbox games could be wrong. This is just a summary of what should be done to make this happen. Of course, Microsoft may use a different approach and for example release "backward compatibility" only as streaming but I believe that would be a huge mistake. Streaming is not real backward compatibility and never will be because it is not free. So I hope Microsoft understands this and will release real native backward compatibility. It is possible and hardware will be really fast. They could even advertise those new PC 2.0 a an AI-PC or any other buzzword like that DISCLAIMER: I work as a software engineer but I don't have any insider knowledge about future XDK. This is just technical speculation about what needs to be done to support native backward compatibility. No leaks \-------------------------------- UPDATE 1 \-------------------------------- I decided to add a classic interview with John Carmack (creator of Doom and Quake ) about unified memory. In 2013 he explained why unified memory will be great addition to the future PC. This is part of his legendary interviews at QuakeCon. I miss those old times. [https://www.youtube.com/watch?v=CcnsJMMsRYk](https://www.youtube.com/watch?v=CcnsJMMsRYk) \-------------------------------- UPDATE 2 \-------------------------------- If someone is interesting about internal design of AMD APUs then they should watch video created by High Yield. Author explained how recent changes in AMD APU Strix Halo allow for faster memory speeds than 112 GB/s. This is much more than just 4-channel memory . This is not directly connected to the subject of “unified memory” because current consoles use monolithic chips but it is still a very interesting. I learned a lot from it [https://www.youtube.com/watch?v=maH6KZ0YkXU](https://www.youtube.com/watch?v=maH6KZ0YkXU) \-------------------------------- UPDATE 3 \-------------------------------- BTW. If someone uses a Windows-based PC handheld and wants to run Windows 11 Full-screen mode with an app other than Xbox, I've created a tutorial on how to do this. No special apps are required. I use only built-in tools in Windows NT and a few basic PowerShell commands. It's a very short step-by-step tutorial with every command explained. On my ROG Ally I replaced the Xbox app with Armoury Crate to create a 'console-like PC' It’s not perfect, but it works quite well. Using this tutorial you can launch any app you like in W11-FSE and additionally learn something about PowerShell commands and Task Scheduler :) [https://www.youtube.com/watch?v=P1NOGW6uBQE](https://www.youtube.com/watch?v=P1NOGW6uBQE) \-------------------------------- UPDATE 4 \-------------------------------- In the comments below, one of the users MooseBoys, noticed that in DX12 there is a flag that allows developers to check if the hardware supports unified memory. This library is shared by both Xbox and PC so the option exists since 2015. AMD APUs return "true" just like Xbox. I didn't know that. **So big thanks to MooseBoys** [https://learn.microsoft.com/en-us/windows/win32/api/d3d12/ns-d3d12-d3d12\_feature\_data\_architecture](https://learn.microsoft.com/en-us/windows/win32/api/d3d12/ns-d3d12-d3d12_feature_data_architecture) [https://learn.microsoft.com/en-us/windows/win32/direct3d12/default-texture-mapping](https://learn.microsoft.com/en-us/windows/win32/direct3d12/default-texture-mapping) So in theory some game developers could check that flag and then explicitly add some optimizations for unified memory on PC even today. But this is a problem: AMD APUs are not very popular among gamers. Even Windows‑based handhelds are very niche products. So in reality nobody would care about this flag. To change that situation, we need a very popular device with AMD APU. A device that would turn this 'forgotten flag in DX12' into a core feature that every game should support. \-------------------------------- UPDATE 5 \-------------------------------- David Plummer (retired MS engineer from Windows team) published a really nice deep-dive video about differences between unified memory vs shared memory. [https://www.youtube.com/watch?v=Cn\_nKxl8KE4](https://www.youtube.com/watch?v=Cn_nKxl8KE4) \-------------------------------- UPDATE 6 \-------------------------------- Deep dive into Xbox APU architecture from the HotChips 2020 conference. Hardware architects from Microsoft explained all the extra features added to the Xbox APU like hardware decompression, virtual GPU memory, VRS 2.0 and much more. Some of those technologies were never used because PS5 and PC didn't support them which would make impossible to create cross‑platform games. But in the future MS could add them to their next‑generation APU for Xbox‑PC [https://www.youtube.com/watch?v=OqUBX2HAqx4](https://www.youtube.com/watch?v=OqUBX2HAqx4)