The default 800x600 seems to be fixed (it's set in the file that's used by sysgen, so the value is probably hardcoded in the image file).
But, you can open up an intent media screen with a size different from the default:
$ dev/ave/dsk/launch -wwidth -hheight
The launch tool has a couple more options, but these are not documented anywhere.
address-suppressed |
Amiga Inc. Faq-O-Matic
When compiling i get 'out of vmem' errors