Int 15 Fn BC  - Phoenix 386 BIOS - Determine CPU Speed For Delay Loops     [b]

   AH = BCh

Return: CF clear
   (Phoenix 1.10 10a) BYTE 0040h:00B0h set to delay loop count
   (Dell 4xxDE BIOS A11) WORD 0040h:00ECh set to delay loop count

Note:  this function reads system timer channel 0 twice, then does
     calculations on the returned values to determine the delay loop
     counter needed by the BIOS for beeps and floppy timeouts