At the Eastern Joint Computer Conference in Boston Digital Equipment Corporation (DEC) of Maynard, Massachusetts, demonstrated the prototype of its first computer, the PDP-1 (Programmed Data Processor-1), designed by a team headed by Ben Gurley.
"The launch of the PDP-1 (Programmed Data Processor-1) computer in 1959 marked a radical shift in the philosophy of computer design: it was the first commercial computer that focused on interaction with the user rather than the efficient use of computer cycles" (http://www.computerhistory.org/collections/decpdp-1/, accessed 06-25-2009).
Selling for $120,000, the PDP-1 was a commercialization of the TX-O and TX-2 computers designed at MIT’s Lincoln Laboratory. On advice from the venture-capital firm that financed the company, DEC did not call it a “computer,” but instead called the machine a “programmed data processor.” The PDP-1 was credited as being the most important in the creation of hacker culture. Some references identified this machine as the first minicomputer; however DEC gave that designation to either the PDP-5 introduced in 1963 or the PDP-8 introduced in 1965.
Reference: http://research.microsoft.com/en-us/um/people/gbell/Digital/timeline/1959-2.htm, accessed 08-25-2009.