On 2023-06-19 18:04, D. Hugh Redelmeier via talk wrote:

Except varous things exploited them.  Like whacking on GPU registers only 
during blanking intervals to avoid tearing.

You may recall the Sinclair ZX80, which had a performance mode which killed the video. If you wanted a display, you got much less performance.
https://en.wikipedia.org/wiki/ZX80