Windows NT on 600MHz machine opens apps instantly. What happened?

Some additional things to note:

Windows NT 3.51 minimum hardware requirements were a i386 or i486 processor at 25MHz or better and 12MB of RAM for the workstation version. So the 600MHz machine with 128MB RAM is exceeding the minimum requirement by (conservatively) 24x in CPU speed and 10x in RAM, along with all the architectural improvements from going from the i386 to what's presumably a Pentium III-class machine.

If that's actually a Surface Go 2 running Windows 11 - well, it doesn't have a quad-core i5 as the tweet claims - the Surface Go 2 came with a Pentium Gold or a Core m3; both with only two cores and of those is an ultra-low power variant.

As such, that exactly meets the minimum CPU specification for Windows 11 and only doubles the minimum 4GB RAM requirement.

I'm not trying to apologize for the difference here, but it's not an entirely like-for-like comparison.

Why is Win11 so slow and unoptimized that it needs such crazy hardware.

I don't think it's unoptimized as much as it's extremely bloated.

The term bloat (as it applies to software) is rooted in gamer-think that has no basis in reality and sends a strong signal of lack of understanding. It's reminiscent of the days of 'BlackViper' and disabling Windows Services -- again, another gamer lack of knowledge issue.

Empty notepad, just started. 82,416K working set in main memory. 25.7MB in dedicated GPU memory. 59 threads. 2 billion cycles spent since launch.

Two threads in !OpenAdatper12 spending ~1.5M cycles per second. Two threads in !recalloc spending ~256K cycles per second.

As shipped, this is no longer a single executable, it is a collection of 230 files, totaling 10.5MB, about half of which are bytewise duplicates, and another significant chunk have overlapping responsibilities, between the icon fonts and png icons.

"Software bloat is a process whereby successive versions of a computer program become perceptibly slower, use more memory, disk space or processing power, or have higher hardware requirements than the previous version, while making only dubious user-perceptible improvements or suffering from feature creep." -- https://en.wikipedia.org/wiki/Software_bloat

I'm not aware of any substantial new features. It uses a new renderer, but this does not produce a significant observable difference from the previous one beyond using more memory. It supports dark mode.