Hey, that's from my Editor ROM page!
So, 4000 series have 1K ram installed. 8000 series has 2K ram. Ignore the colour info obviously.
The last 4000/8000 PET motherboard revision is called the "Universal Dynamic PET" motherboard. It is configurable for either 40 or 80 columns depending on jumpers installed plus memory chips etc. In the day you could install a big switcher to toggle between them, or install a 3rd-party board that used a bunch of multiplexer chips to do it for you (keep looking on my pages for an example
. Anyway, 1K or 2K is the normal amount of video ram that the "normal" PET machines used.
After the 4000/8000, Commodore released the 8296 machines. Its motherboard contained 128K ram. Like the C64, the entire address range can be ram if properly configured. Anyway, the CRTC video chip could access up to 8K (from $8000-$9FFF) as video memory. By re-configuring the CRTC chip registers you could set up alternate screen layouts. For example, a 100x30 character screen, or you could set the CRTC to only use 4-line high characters then double the rows to 50 (ie: 80x50 characters). By installing a special font rom you could get 160x100 "pixel" graphics (I have done this!). Of course there's no firmware support for these things but the CRTC chip is quite flexible.
Steve