The modest sales of the PDP-1 set the stage for Digital’s next step. That was to establish a close relationship between supplier and customer that differed radically from those of IBM and its competitors. From the time of its founding, IBM’s policy had been to lease, not sell, its equipment. … That policy implied that the machine on the customer’s premises was not his or hers to do with as he wished; it belonged to IBM, and only IBM was allowed to modify it. … The relationship DEC developed with its customers grew to be precisely the opposite. The PDP-1 was sold, not leased. DEC not only permitted, it encouraged modification by its customers. … This policy of encouraging its customers to learn about and modify its products was one borne of necessity, The tiny company, operating in a corner of the Assabe Mills, could not afford to develop the specialized interfaces, installation hardware, and software that were needed to turn a general-purpose computer into a useful product. IBM could afford to do that, but DEC had no choice but to let its customers in on what, for other companies, were jealously guarded secrets of the inner workings of its products. DEC found, to the surprise of many, that not only did the customers not mind the work but they welcomed the opportunity.
Paul E. Ceruzzi, A History of Modern Computing (2d ed. 2003), pp. 128-29.