One doesn't have to go that far back. I bought an ASUS Eee 900A. It had an 8GB SSD... and Xandros, set up to use UnionFS so you could go back to the original state easily. I took it home, powered it up, and it promptly downloaded enough new versions of packages that the SSD was filled and it hung.

I wiped Xandros, installed what was called Eee Ubuntu (now Easy Peasy) and never looked back (though I since got a bigger SSD, maxed it out on RAM, and happily run Bodhi Linux)--but I can only imagine the wrath of someone who bought one and didn't know that was an option, especially one bought as a gift. I had to wonder whether it was set up to fail.

Not quite. As far as I can tell DOS 3.3 was distributed on one disk for the core OS and commands (~1MB). There were supplemental disks for Basic etc. Windows 3.1 was larger but so were "standard" disks of that time (it was on 7 1.44MB floppies, compressed, but parts were optional).

But there is one huge difference you have overlooked - with your 486 you could install any operating system you wanted. You could even delete bits of DOS you didn't use. With the Apple/Microsoft tablets you can only run the operating system they provide (cryptographically/hardware enforced) and you cannot delete any of the OS.

With that 20MB 486 you could choose what every single byte is used for - and that is true of PCs today. But not for the locked down hardware.

The surface pro is not afaik locked. It's a pc that happens to be made by Microsoft.

I thought MS's ARM-based devices would refuse to boot anything that is not cryptographically signed with a set of MS-controlled keys. If that's still the case, then they're pretty locked in my book.

The Surface Pro is not ARM-based.

We won't find out until mid-February exactly what the Surface Pro situation is in terms of device locking, administrative access etc is.

Goes back further, even the C64/C20 was hard to squeeze the whole ram out of unless you wanted to scratch build everything. Even a Timex 1000/zx81 didn't get full use of the 2/1k ram. I'm thinking this has been standard literally forever (I'm assuming no one argued over usable space v total space pre-transistor).

That doesn't mean it's right of course - space post-os would be a great spec to have. Also a motivation for more people to question why. A lot of the overhead (CPU, ram and long term storage) on a regular computer or phone is there for good reasons, but I would venture to say the majority of "no-load load" is questionable at best.