BX or BX-2
If u have a BX, u may use only P-II/450. Last BIOS 12.
If u have a BX-2 board and BIOS 17, u may use P-III 850.
Check your board and remember board ID. Now have a look to Intel homePage and board specification. No on every BX-2 works 850. Oldest boards supports onlu 650.