C H S in a Compact flash

The concept of CHS is since long outdated. But.. It depends in what context you use it. If it's an old machine with x86-BIOS you usually enter heads=63 sectors=255 There are three translation modes for x86-BIOS calls (INT 13h) to physical sectors CHS, LBA, and Large. Try to use LBA if that won't work use Large or as last resort CHS mode.

If you build a system that is free from x86 baggage then LBA is the mode to use.

Furhter reading: *

Issue the identify command to the card and parse the sector worth of data that it returns. It's all in there.