Mark Sandles

Hi all... excited to get something going...I've been following Andrew Davie's excellent tutorial on this site and have a question regarding a begginers kernel program... if I cut and paste the 1st version in the tutorial then the output isn't what I'd expect...there is a black gap after the 192 display screen scanlines then another a thin stripe..then it spills back to the top of the screen... however if i alter the code turn the vblank off directly before I output the display..it's more pleasing to the eye.. is this acceptable or will I have problems in the future doing it this way? if so...what was reason for having it other way?...is it to do with my setup? Thanks Mark