Actually, the Quadra 900 and 950 both have the same SCSI controller,            (running at different speed).  They are not SCSI 2, but can support
certain SCSI commands that take advantage of faster drives.  The
I/O processors are present on both machines.  The Q950 runs its
I/O bus at 25MHz, while the 900's I/O bus is 16MHz.

The Quadra 950 supports 16bit color on all monitor sizes, as well
as 24bit up to 832 x 624 resolution.  It also supports 1024 x768
resolution.  The 900 supports supports 8bit at 1152 x 870, and
does not support 1024 x 768 at all.

VRAM on the 950 is 80ns or faster, and 100ns or faster on the 900.