Intel Slot 1 processors come in 3 formats:
SECC: found on Intel Pentium II processors. Black plastic and metal cartridge which covers the entire unit. SECC stands for Single Edge Contact Cartridge
SECC2: found on very late Pentium II processors, and all Slot 1 Pentium III processors. Black plastic cover over the front of the unit, with an exposed back side for the HSF unit. Processor die is mounted in an OLGA (organic land-grid array) FC-PGA style, which allows for best contact and cooling.
Intel now calls both SECC and SECC2, SC242.
SEPP: Found on all Slot 1 Celeron processors. Exposed PCB with processor. No plastic or metal covering.
Slot A: Physically the same as the Intel SECC unit, except that it is facing in the other direction. Electrically they are completely incompatible.