>re-opening the file and skipping to where you left off That's what Windows does now. But I think in the past it wasn't that way (as suggested by the sources).

>re-opening the file and skipping to where you left off That's what Windows does now. But I think in the past it wasn't that way (as suggested by the sources). In my tests it appears that the command processor caches the byte offsets of each line, so it's possible to GOTO any line in the past without rescanning the whole file.