[lordfrito]

RAM was too expensive to have two full frame buffers with page flipping. So they resorted to timing tricks.

Many times the RAM was dual ported (CPU writes while video hardware reads).

Other times they'd do clever clock tricks... for example, using 10 MHz capable RAM, generate a 10 MHz clock, and divide it down to two different 5 Mhz. One 5MHz clock is sync'd to the rising edge of 10 MHz, the other is sync'd to the falling edge. Sort of "interleaving" the two 5 MHz clocks. Total clock rate is 10 MHz, but the two 5MHz hardware circuits are out of phase and don't interfere with each other.

Later on, as RAM prices fell and double buffered images became economically possible in arcade machines, true page flipping started getting used, they would simply isolate the CPU and video buses from each other as the frame buffer was flipped. I know this is how things worked on I, Robot (1984)... this technique could have been used earlier but not much as not many games had real frame buffers at the time.