I'm reading a book called The Friendly Orange Glow, about the PLATO multiuser computer system developed by the University of Illinois in the late sixties, which is fascinating at several levels as a microcosm of an alternate universe of computing. The particular aspect I'm looking at here is the source of the orange glow, the plasma screen, a key enabling technology for the system.
PLATO used a 512x512 monochrome bitmap display, which apparently cost $2500. (I'm not clear whether that's just for the plasma screen itself or for the entire terminal, which contained additional components such as a 16x16 touchscreen input.) That's a quarter million bits (32 kilobytes) of data. On a CRT or LCD, it would need to be backed by a quarter million bits of video memory. According to https://en.wikipedia.org/wiki/Magnetic-core_memory in the early days of magnetic core, that would've cost a quarter million dollars; even by the early seventies, it would still have been $2500 of video memory, doubling the total cost of the display.
But apparently a plasma screen has the remarkable property that it does not need refresh, i.e. it doubles as its own video memory. And for a few years, that was a key advantage.
I'm trying to reason about what it would be like to use such a system. For example, scrolling would not be a primitive operation. You would always have to redraw the display based on internal data (whose format would be optimized for compactness, not speed of redraw), so it would be natural to design around 'page at a time' instead of continuous scrolling.
I'm also trying to figure out what would be the implications of the display persisting without refresh. It occurs to me that might depend on timescale; just because the display doesn't need refreshing every 1/60 of a second, doesn't necessarily mean it persists forever.
Just how long was the image on a 1970-era plasma screen stable for?