Maybe it means that it won't work with computer with less than 640K installed (i.e.: Amstrad PC1512, original IBM PC, Sinclair PC200) or in computers with weird memory maps that don't have 640K contiguous.

This can actually become quite a technical discussion and, since I'm not a programmer myself, I'll just briefly try to explain - and I stand corrected.

The 640 KB barrier is an architectural limitation of the original IBM PC and compatible PC's and hence why older games "only" required 640 KB of RAM, since they were written to be run on XT based PC's.
However, whereas earlier games might have been able to get away with only 64 KB or 256 KB of RAM, as technology and graphics became more advanced, later games required a bit more conventional memory (up to the 640KB RAM that was available to DOS programs).

To expand a bit on the above, games that does make use of a DOS extender, like DOS4G/W (i.e., runs in protected mode) are not limited by the 640 KB barrier.
However, games that runs in "real" mode requires a certain amount of base (conventional) memory to be free (available) in order to execute the program.
If your system's drivers and device drivers takes up too much of this conventional memory, then the application will fail to load. In some cases, certain drivers and device drivers could be loaded into the upper memory area to free up some conventional memory.
Some applications were written to make use of "expanded" memory but this must not be confused with "extended" memory, which is a totally different concept and, under DOS, required an extended memory manager in order for applications to gain access to it.
However, games that require more than 640 KB of RAM, and ran in "real mode", would normally still require a certain amount of conventional memory to be available.
In such cases, many game developers suggested making use of a boot disk before executing a game, in order to ensure that the maximum amount of conventional memory was available and that only the necessary drivers were loaded (like a mouse and/or CD-ROM driver).

Some more reading material to explain the differences between the different "types" of memory:
https://en.wikipedia.org/wiki/Conventional_memory
https://en.wikipedia.org/wiki/Extended_memory
https://en.wikipedia.org/wiki/Expanded_memory

It just means you have to have at least 640KB of memory installed - nothing more.

It's a minimum recommended hardware spec, not the required free resources.

infiniteclouds wrote:

I find this requirement on games a little confusing. Between DOS and drivers there will always be memory eaten up - does this essentially mean that such games will always require a system that has more than just conventional memory?
Usually those games will say something like "2MB required", I thought.

It's similar to today, I think. The requirements are just an approximate value and reflect the standard specs of their time.
In the later years of PC/XT machines, 640KiB were simply common and DOS 4 was around the corner, requiring more memory for its own.
In reality, if you your're running the more light-weight DOS 2.11 or DOS 3.3, 512KiB of memory were fine as well.

Also, 640KiB were considered the maximum "DOS memory" (conventional memory).
So it's also an indicator that the game needs nothing more than that (no XMS, EMS).

Mobygames simply takes over those specs that were written on the original box.

kixs wrote:

It just means you have to have at least 640KB of memory installed - nothing more.

You are laughably wrong. I don't think you understand the concept of the 640k issue.

evoportals wrote:

kixs wrote:

It just means you have to have at least 640KB of memory installed - nothing more.

You are laughably wrong. I don't think you understand the concept of the 640k issue.

I don't see anything "laughably wrong" with his statement. Yes, "640K required" is an incomplete requirement as it doesn't specify how much of that needs to be free. But it was an indication for people with 512K or less systems that there's no way they will be able to run the program, even with a boot disk.

All it means is that MobyGames doesn't have a selectable entry for the *exact* amount of RAM that every game really needs (there's "640 KB" and the closest one below is "512 KB"). So when people submit the system requirements they'll typically round it off to the next-highest one. Although if they want to be precise they can type the actual number into the "Notes" section of the system requirements.

E.g. a game's manual may say it needs 580 KB / 610 KB / etc. conventional RAM, but on Moby all of that will be filed under "640 KB".

evoportals wrote:

kixs wrote:

It just means you have to have at least 640KB of memory installed - nothing more.

You are laughably wrong. I don't think you understand the concept of the 640k issue.

You know, you can also explain why do I make you laugh and what has the 640KB issue anything to do with the requirements of the game/app?