All models with BIOS v2.20 and earlier are compatible with FMCB. All models with BIOS v2.30 and later will not boot FMCB at boot up.
Originally Posted by wisnoskij
As for the SCPH-90000 series of PS2s, consoles with a datecode (If it has one) of 8b (The second quarter of year 2008) and before will have BIOS v2.20. Those consoles with datecode 8C (The third quarter of year 2008) might have BIOS v2.30 instead of v2.20, and those with a datecode starting from 8D onwards are doomed to forever never launch FMCB at bootup.
Only the SCPH-90000 series of slimline PS2s and the PS2 TV have models that won't boot FMCB at bootup, so if you are unsure, just get an older slimline or a FAT PS2.
All PS2s have the same level of compatibility in all ways (Excluding the ability to look for OSDSYS updates and hence boot FMCB). The laser might be weaker in some units and the CD/DVD drive tray might be weaker in some older FAT PS2 models, but everything else remains about the same.
Oh, and the original SCPH-70000 (v12) series has a problem with the laser getting blown on it's own, even if you don't do anything (Like installing a modchip).
Unmodified SCPH-77006 with SM 3.6
SCPH-39006 with M-chip modchip, SCPH-10281 NA and refurb Seagate 80GB HDD
SCPH-10000 v1.00 with SCPH-10190 PCMCIA NA and SCPH-20400 HDD unit