scsi cable length

[Steve Chen]

hello,

I am not sure if this topic has been covered before but if it has 
my apologies for the bandwith.

I would like to know if the following are the exact limits for 
scsi cables (before problems occur).

scsi I (centronics):    		20 feet
scsi II (micro-D 50-pin, and DB50):	10 feet
scsi III (micro-D, 68-pin):		10 feet

In addition, has the scsi cable length ever been the culprit even
when it is less than the specified limit?

thanks in advance,
Steve 
steveywc at uci.edu

ps: the total length = one end of the internal scsi cable to the
    other end of the external cable? (as oppose to just the total
    external cable length)