[a1369209993]

> Imagine MS would open source Windows XP SP2. [...] I don't think anyone would build an OS better than modern Win10 from that code.

Uh, yes they would? It's literally trivial - you just hit compile. As you note, a 64-bit build did exist, so it's not even limited to now-obsolete hardware, although unless you want to call some of the things at [0] automatically better than XP just because they run on amd64, even that wouldn't disqualify it from being better than windows 10.

0: https://wiki.osdev.org/Projects

[Const-me]

> it's not even limited to now-obsolete hardware

That's not correct, it is limited. The primary reason being GPU drivers, Vista switched to hardware compositor, as a side effect they reworked kernel API of GPU drivers. I don't think Intel, NVidia or AMD ship drivers for WinXP x64, or Server 2003, for their current generations of products. To lesser extent, same applies to the rest of the hardware: I don't expect it's easy to boot XP from NVME SSD, or support modern flavours of wireless like 802.11n or BT4.

Software is even more diverse, vast majority of modern apps won't run on XP64. For the software that I currently work on, the largest missing pieces are Direct3D 11, Direct2D, DirectWrite, Media Foundation, and .NET framework. These components are huge, Microsoft spent many millions to make them.

Windows is not just code, it's an ecosystem.

[Shared404]

Isn't there a fallback driver that almost all graphics cards support?

It seems like if anyone wrote a single implementation of that it would work.

[Const-me]

Depends on your definition of “work”.

The driver is called “basic display adapter” or something like that. Modern Windows is barely usable without 3D GPU acceleration. Too many pixels to render and doing that on CPU is too slow, especially so on laptops. Vast majority of modern software, web browsers included, normally use a 3D GPU to render. And since Vista, windows desktop compositor, dwm.exe, uses a 3D GPU to compose windows into desktop.

Old Win32 apps working on XP will be OK, though. WinXP shell didn’t require nor use a 3D GPU, and very few apps of the era were using GPUs. Unless you have too many pixels in the display, or the app in question renders 3D graphics of any sort, the performance probably gonna be adequate.

[a1369209993]

> Modern Windows is barely usable without 3D GPU acceleration.

That is a specific example (admittedly only one) of why Windows XP is better than Windows 10, so I'm not sure why you're citing that as if it supports your point.

[Const-me]

> admittedly only one

Other hardware requirements are much lower too, XP will work on Pentium 233 MMX with 64MB RAM, Win10 requires at least 1GHz CPU and 1GB RAM. Some old software, and many old device drivers, won’t run on Win10 even if the OS is 32-bit.

> why Windows XP is better than Windows 10

The hardware evolves just as fast as the software. If you run XP on modern PC with a 4k display, I don’t think it will do great even if you’ll manage to install a 3D GPU driver (you probably need some GeForce 900-series GPU to try that, or maybe virtualized VMware GPU will do). If you run Win10 in 800x600 resolution, will probably work OK even with that basic unaccelerated driver, will render on CPU.