IBM 5170 6MHz or 8 MHz

[MaTel]

I hope its not a stupid question...
how can i recognize a 6mhz or a 8mhz board?

 

[modem7]

Check the crystal - the metallic 'can' close to the CPU.
12Mhz crystal = 6 MHz operation. 16Mhz crystal = 8 MHz operation.