>>6014
>512MiB
Oh, that's plenty.
OpenBSD relinks the kernel every boot, I think 512MiB is just a little more than enough to do it, I didn't recommend it because I assumed you had less RAM. OpenBSD runs on architectures that never had a machine with nearly as much RAM, but those have it disabled. Generally, if OpenBSD runs on a machine, then it works well, they just drop support for the hardware (or the whole architecture) if it doesn't. OpenBSD has a floppy installer that's a single floppy, it downloads the rest of the system over the internet, although it can also load the files from a storage device if the install floppy has the drivers for it.
Void Linux Musl can get a MATE desktop with 100MiB of RAM usage. I don't recommend using MATE in specific though, go with a tiling WM like dwm, they're both more convenient (after you learn them) and lighter on resources, I just haven't done that on Void to tell you the RAM usage. Avoid i3 because it's the more bloated one of the tiling WMs, if you like it then bspwm is a lot like i3.
>but the cdrom wasn't recognized
Late 90s/early 2000s laptops generally have poor support for various boot methods. Not sure if it's a NetBSD issue in your case but it wouldn't be uncommon to be unable to boot over anything but floppy and the internal hard drive. Another thing is that Linux users commonly burn the USB image into a CD or the CD image into a USB, the BSD installers aren't hybrid, so make sure you didn't do that.
If all else fails, netbooting seems to have been well supported throughout the 90s.
The smallest systems that I know of are OpenWRT, Alpine Linux, Hyperbola Linux, Gentoo Linux, and NetBSD. I have Hyperbola and Alpine VMs that use around ~22MiBs of RAM each. They're pure command line systems, I use them for programming. OpenWRT is even smaller, falling to 11MiBs or so of RAM usage, but its package repositories have few packages that you wouldn't run on a router.
After that, OpenBSD and Void Linux Musl are lightweight for modern standards. I haven't used Tiny Core Linux to compare. OpenBSD in a VM starts off at around 49MiBs of RAM usage without a GUI and 70MiBs of RAM with the default GUI, keep in mind VMs use less memory because of simpler drivers and less hardware. Void is comparable to that, I don't have exact numbers.
Gentoo, despite being able to produce very small installs, is a bad idea on old hardware because of compiling, so unless you use a different machine to compile programs for it don't bother.