Note this: "However, Apple eventually began shipping all Apple IIs with 48k following a drop in RAM prices and so this was no longer an issue. " The 16k/32k/48

Note this: "However, Apple eventually began shipping all Apple IIs with 48k following a drop in RAM prices and so this was no longer an issue. " The 16k/32k/48k that apple shipped was the total ram in the machine. VisiCalc had to fit there to - no swapping/overlay was employed. 26(cols)1K(rows)2(bytes) is already 52KB. They were obviously storing things more sparsely than that - I think it was 100 rows or even less (which, at 2 bytes/cell would be in line with your 5K estimate). However, 2 bytes is not enough for floating point values, and cells could also contain text. Whatever it was, it was more complicated than the simplest array, though probably not by much.