Second Class Macs are Apple's somewhat compromised
hardware designs. For the most part, they're not really bad - simply
designs that didn't meet their full potential. (On our rating scale,
the more brown apples, the worse the hardware.)
I resisted adding the Macintosh IIfx to the Second Class Macs list for
a long time, but I finally concluded that it does belong on the same list
as the upgrade-challenged IIsi.
Like the IIsi, the IIfx is a very competent machine. In fact, until
the Quadra 700 came out, it 
was by far the fastest computer Apple made. In fact, until a
lot of applications were recompiled for the 68040, they ran faster on
the IIfx than on any Quadra!
The IIfx was the first Mac to earn the label "wicked fast" - which
it was. And it's still a very competent performer.
So what makes it a Limited Mac?
- SCSI voodoo: Some SCSI devices will work just fine (I've had very
good luck using drives with active termination), but others have not
been so fortunate. The IIfx needed a special "black" SCSI terminator
for most devices, a terminator unique to the IIfx and difficult to find
if lost.
- Memory: This was Apple's only computer to use very fast memory with
latched read and write. The 64-pin SIMMs are harder to find every year.
If you are in the market for a IIfx, be sure you can locate memory
before you buy one.
- No upgrade path: There were a few accelerators that could boost the
IIfx into the 45-55 MHz range, but it was the last Mac to use the big
six-slot Mac II case.
- Unfilled promises: The IIfx had a pair of helper chips (10 MHz 6502
CPUs) designed to process I/O while leaving the 40 MHz 68030 free from
handling I/O, but the OS was never optimized for this technology.
The IIfx is an incredible machine (we also rate it a best buy on the used market). It has six NuBus
slots, room for a 5.25" hard drive, a 40 MHz system bus, a built-in
level 2 cache (Apple's first), and room for 128 MB of memory - if you
can find it. It's a powerful server and still a very decent user's
machine. If not for the SCSI and memory issues, it wouldn't be
listed as a Second Class Mac.
