
8 MB SIMMs do not have to be composite SIMMs, although many (most?) 16 MB 
SIMMs are.  72-pin SIMMs allow two memory banks per SIMM, thus permitting 
the use of 4 Mb DRAM devices (the same ones used on 4 MB SIMMs) to be used 
for two 4 MB banks on one SIMM.  I can't imagine that it would be cheaper 
to build an 8 MB SIMM using 1 Mb DRAMs as the 4 Mb parts reached (and 
exceeded) bit for bit price parity with the 1 Mb parts some time ago.  
It's probably possible to build a single-bank 8 MB SIMM using 4 Mb parts - 
this could cause problems in a Q800.  I'm not sure why you'd want to do 
this, though, as a dual-bank 8 MB SIMM would be cheaper to build than a 
single-bank composite one.