FetchMode

AGA hardware allows bitplane data to be fetched by the DMA in 16,32 or 64 pixel
groups. The larger fetches give the processor more bandwidth, this is especially
noticeable with AGA Amiga's running without additional fastmem.

When using increased fetchmodes bitplanes must always be a multiple of 64 pixels
wide.

Those wanting to attempt DisplayAdjusts on displays with larger fetchmodes will
encounter severe difficulties in creating a proper display. We think it is actually
impossible for displays to run at fetchmode 3 with more than I sprite without having
to adjust the display to around 256 pixels across.