In the simplest case you need one transistor per row and one per column for bitmap displays. If any transistor in omitted, than that row or column must have a

In the simplest case you need one transistor per row and one per column for bitmap displays. If any transistor in omitted, than that row or column must have a fixed voltage, which means that the corresponding column or row of pixels would no longer be controllable and they would display the same pixels as whatever other column or row is selected at a given instant. One thousand transistors do not need a huge space (they would fit easily on a PCB of a size compatible with a PLATO terminal, based on the photo from Wikipedia), but they were quite expensive. Suitable high-voltage integrated circuits have appeared later. In 1972, one could have used Nixie decoders like 74141 for the negative voltage, replacing 512 transistors with 64 IC packages, but 512 discrete transistors would still have been needed for the positive voltage. For segmented alphanumeric displays you need only 14 or 16 transistors for the segments plus one transistor per character.