[II2II]

Different people are going to have different experiences, based on what they had and what they used it for.

If you've ever used a 68000 based Macintosh, you were limited to 4 MB RAM and 1 MB seems to have been more typical. It's in a different league to be sure, black and white graphics and multitasking was optional prior to System 7 (and I don't think multitasking was shipped with the System Software until System 6). That removes a lot of the pressure on memory. On the other hand, you had early Amigas supporting both colour and multitasking. The 1000 shipped with 256 kB RAM and 256 kB ROM (though I think 512 MB RAM was more typical). For an Apples to Apples comparison, the original Macintosh had 128 kB RAM and 64 kB ROM.

Windows 3.x and OS/2 2.x were later in the game, so they were designed for systems with more RAM. They also supported virtual memory. That meant there was less pressure on developers to write memory efficient code. I'm not really qualified to judge realistic memory requirements for OS/2 since I only used Warp on a system with 16 MB RAM, but I recall many people using Windows 95 on systems with 4 MB RAM. The requirements for both operating systems were similar. It's also worth noting that Windows 3.11 was rather late in the game. The system requirements were climbing rather quickly at that point.

[marssaxman]

The "MultiFinder" extension allowing cooperative multitasking was actually included with "System Software 5", but I don't think I used it myself until System 6.

[lproven]

Same here. It was at least marginally more stable on "System Six."