The DEC Type 30 was an early vector graphics display, that was used for an astonishingly wide range of applications for the 1960s. It used a 16-inch circular CRT with high persistence phosphor originally designed for use as a radar screen, and the resolution (presumably determined by the DEC-built digital electronics) was 1024 x 1024.
I've been trying to look up just how quickly it could refresh, and the figure I'm seeing is one operation every 50 microseconds, which seems straightforward enough, but https://www.masswerk.at/nowgobang/2021/spacewar1
The PDP-1 is capable of displaying a maximum of 20,000 dots per second — assuming our program doesn’t anything other than issuing display command. Which gives us, with a reasonable frame rate for a flicker free display of, say, 18 fps, about 1,100 display instructions per frame, which is just good enough for a single line accross the display.
That didn't look quite right, so a bit of searching found what looks like an original manual, http://www.computinghistory.org.uk/userdata/files/digital-precision-crt-display-type-30.pdf
Discrete points may be plotted in any sequence at a 20 kilocycle rate (one point every 50 microseconds)
Okay, that does seem to confirm.
... huh? In a vector display, the fundamental operation is not plotting a point but drawing a line between two points. That's useless if what you want to show is a photograph, but great for things like circuit diagrams, molecule diagrams and suchlike visibly geometric things that were representative of early graphical applications.
If you can only do one point at a time, well it will still work in principle, but effective performance will drop by orders of magnitude, and you lose the ability to draw lines at angles that don't necessarily stick to the grid of points defined by the resolution.
Did the Type 30 really only draw one point at a time? If so, why? Had a vector display just not been thought of yet, or was there some other reason it couldn't be done?