I would like to get a clear explanation of the Turbo mode function in relatively simple terms.

My understanding is as follows:

i7 920 Turbo on + load on 4 cores = 21 Multi
i7 920 Turbo on + single-threaded load = 22 Multi (but this would drop to 21 if there is any load on the other cores)

Originally Speed Step needed to be enabled in order to implement Turbo but manufacturers have coded the bios in such a way as to circumvent this requirement and allow us to use Turbo for a permanent 21 multi and 22 in single-threaded apps.

Am I right on this?