Re: Disk drive speeds

[Jorge <user@nospam.com>]

damage_x@hotmail.com writes:

>Video does eat up a lot of cycles but I think the 40x24 text display
>uses up less than a third even on NTSC systems. Most displays wouldn't
>use much more than that. The worst case scenario probably is around
>half though.


Actually standard text screen (OS mode 0) is the worst case. This is 
because text screen on the Atari is bitmapped from the point of view of 
DMA. The "font" is always stored on main RAM. So ANTIC has to fetch the 
characters bitmaps, same amount of bytes as the highest graphics mode, 
*plus* the characters themselves. At a standard text screen, ANTIC steals 
36% of CPU cycles on NTSC.

The best case is, of course, nothing (blank screen without DMA). But even 
then ANTIC steals some cycles for RAM refresh.