Is "512 MB RAM or more" a good description of harware requirements of JOSM?

[mkoniecz]

I would expect JOSM to use more RAM to be working well

Such claim is at ​https://wiki.openstreetmap.org/wiki/JOSM/Installation and ​https://wiki.openstreetmap.org/wiki/Pl:Instalacja_JOSM#Wymagania

Is it actually correct?

It is not on https://josm.openstreetmap.de/wiki/Help/SystemRequirements

[taylor.smock]

It depends upon how much data you load in to JOSM. The absolute minimum requirement to run JOSM (after startup) is ~100 MB after a manual GC. This is with no data loaded.

For example, with Mesa County GIS Valleywide 2020 loaded, the memory usage for 39.0637818;-108.5670233;39.0660809;-108.5620022 increases to a peak of 1371 MB, and naturally decreases to 336 MB. After a manual GC, it goes down to 210 MB. For 39.0635819;-108.5719585;39.0782418;-108.5513592 with the same imagery layer, it increases to a peak 1398 MB and naturally decreases to 402 MB. With a manual GC, it decreases to 218 MB.

For the purposes of minimum hardware requirements, I'd use the post-GC numbers. But I'd highly recommend 512 MB or higher -- anything lower, and you are going to have a lot of time spent in garbage collection (GC). And most people should just use the defaults (4096 MB, IIRC), since it will allow JOSM to keep more stuff in memory (like image tiles). And some plugins also cache stuff in memory.

[skyper]

I have no problem running JOSM with -Xmx256m but it heavily depends on the workflow, installed plugins, active mappaint styles, amount of loaded data and imagery in use.
With -Xmx768m I usually get no problems using up to five different imagery layer but I usually do not load big/huge bboxes with complete data.

The default should be set by the JRE on 64bit OSs, see ​https://stackoverflow.com/questions/4667483/how-is-the-default-max-java-heap-size-determined.