Here's is a letter I wrote to the mighty Brian Strain / Games Guru:
Just wrote in to say that the Games Guru article is great. I've been
coding the C64 for many a year now but it's a great article for people just
starting off. Could you give me a listing on how to remove the side borders
of the screen, I know how to remove the top/bottom borders but the only
way I can see to remove the side ones is to use all the raster time!
Just a little tip I have now for C128 owners. To get 2 MHZ in C64
mode!!! just "POKE 53296,1" the screen will fill up with junk but you are
in 2MHZ mode meaning basic and machine code will speed up by X2!!
The best way to use this mode is to use the poke to go into 2MHZ
mode and then switch off the screen (POKE $D011,$0B), This mode is ideal for
Cool raster demos and the like, but you can't display text or graphics in
the mode unless you have a C128 RGBI monitor. Remember this 2MHZ poke works
ONLY for the C128!.