CF-28 came with 600 MHz (Mk1), 800 MHz (Mk2), or 1 GHz (Mk3). Mk2 and Mk3 are very similar except for CPU speed, Mk1 has subtle differences in the case, HD caddy, and others. Mk1 maxes out at 512 MB memory = 256M on-board and a 256M stick of PC-133. Mk2 and Mk3 can handle a 512M memory stick for 768M total, BUT only certain kinds of low-density 512M memory will work like Kingston, Crucial, and "Buffalo" brand.
Panasonic power adapter is CF-AA1639A has 15.6V @ 3.85A with a center pin, different than newer ones with center hole for Cf-18/19/29/30/etc.
ToughBooks: CF-74 73 53 52 51 31 30 29 28 27 25 19 18 08 07 C1 C2 F9 H1 M32 M33 M34 R2 S10 T8 T5 T4 T2 U1 W2 Y2 VDW07 PDRC ...
GoBooks: VR-2, XR-1, IX-260+, IX-350