Your Macintosh has a certain amount of random access memory (RAM). A standard Macintosh, whether a Plus, an SE, or a II, comes with one megabyte of RAM, or roughly one million characters worth.
RAM is somewhat similar to human short-term memory - it is impermanent and more limited in capacity than long-term memory (disk storage).
When data are received from another computer, RAM is allocated to hold the data. Opening editor files and typing new characters into them uses up memory, and so do opening desk accessories, using the Cut, Copy, and Paste commands, and so forth.
As more and more data arrive, there will be less and less unallocated (free) RAM remaining. Eventually, so many files may be open and so much data in those files that there is hardly any free RAM left. When this happens, TOPS Terminal senses the problem and informs you of it.
A window comes up telling you that memory is filling up and giving you a choice of actions you can take to prevent complete filling. The most useful things to do are to close some files, to clear lines off the top of a session transcript, and to stop capturing lines off the top of a session transcript. These actions will either free more memory, or cause memory to stop being used up by the arrival of new data.
If you don't do anything or don't do enough to free up memory, TOPS Terminal takes some emergency actions to prevent memory from becoming completely full.
It will try to close open desk accessories, to disable menu items like Open and Terminal Session which could cause more memory to be used up, to close editor documents which have not been changed, and to turn off capturing in documents connected to other computers.
If these actions don't work, then TOPS Terminal will take last-ditch emergency measures: break all connections to other computers, save all files, and quit back to the Finder. Running completely out of memory would cause the Macintosh to crash, so these actions are preferable to crashing; but the last-ditch actions would very rarely be invoked, since the first-try emergency measures ought to prevent memory from running that low.
In any case, a little caution on your part may be required to prevent the emergency measures from being invoked.
