I didn't realize at the time how fortunate I was to have a Tandy 1000HX when I was growing up. It was one of the only PCs I'm aware of which had DOS in ROM. Of course you were stuck with DOS 2.2 or something. But startup times were beyond almost every device I've used since, and certainly miles ahead of any PC.

Here's a quick demo from a similar Tandy model: https://www.youtube.com/watch?v=DaSkda4XW3k

Acorn also had RISC OS in ROM. Booted in about two seconds. Yes it was tricky when you had to upgrade but I suspect the constraints made the ROMs better quality. Certainly was rare to come across bugs etc and the performance was miles ahead of the current software we have today.

I upgrade the OS for an Acorn A3000 around 30 years ago. It wasn't too bad. Carefully remove the old ROMs from their sockets and carefully push the new ROMs into the now empty sockets. Quickest OS upgrade I've ever done.

Fun fact! Risc OS is some quasi open source these days - ie you can see the source.

It's in ARM assembler.

The IBM PS/1 had MS-DOS 4.01 in ROM. You could install newer versions on the hard drive, but I remember being bitterly disappointed on installing the 2.5MB RAM expansion, because the memory test slowed the boot process down tremendously.

Yeah, that's what I was thinking. Everything from my TI-99/4a to my Apple IIc were basically like turning on the radio. Instant. But that's mostly because they didn't really do ANYTHING at startup.

Do you also remember waiting 5 minutes for a game to load from the insanely slow 1541 floppy drive? I'll gladly take a 10 second boot time with instant application start time over instant boot time with 5 minute application start time.