circuit boards plugged into such backplane the performance characteristic may be for example component speed operating protocol etc system start up is interrupted upon detection of such incompatibility after start up upon plugging an additional printed circuit broad having an electrical component thereon with an operating incompatible with the electrical components on the plurality of printed circuit boards into the backplane the electrical component on such additional printed circuit will not be electrically coupled to the electrical component on the additional printed circuit board from the electrical components of the plurality of printed circuit boards application_number US 60687203 A description referring now to fig1 a data storage system 100 is shown for transferring data between a host computer server 120 and a bank of disk drives 140 through a system interface 160 the system interface 160 includes a plurality of here 32 front end directors 180 1 180 32 coupled to the host computer server 120 via ports 123 1 123 32 a plurality of back end directors 200 1 200 32 coupled to the bank of disk drives 140 via ports 123 33 123 64 a data transfer section 240 having a global cache memory 220 coupled to the plurality of front end directors 180 1 180.