Intel Mobile Pentium II 266
This engineering sample of the Mobile Pentium II has been manufactured in the last weeks of 1997 (week 51). That is 15 weeks before the official launch of the Mobile Pentium II 'Tonga' core. Technically it's an Deschutes core (0.25nm, half speed off-die L2 cache) but with a 66MHz FSB instead of 100MHz.
The Tonga-core based CPU's are available in 233, 266 and 300MHz models. Later models with the (faster) Dixon core came in 266MHz and 300MHz models as well but also featured 333, 366 and 400MHz models.
I haven't tested this engineering sample since I don't have a compatible laptop to test it in so I can't verify clock-frequencies and CPUID's. This CPU needs a 'Mini-cartridge' socket which I believe is indicated as MMC-2. I have two Pentium II laptops but both are MMC-1.