History of the Collection

The PDPplanet collection began with Paul Allen's purchase of a Toad-1 system from XKL Systems Corporation (now XKL LLC), an engineering firm in Redmond, Washington. Mr. Allen was interested in preserving the historically significant software that was created on the PDP-10 systems from Digital Equipment Corporation, the famous DECsystem-10 and DECSYSTEM-20 mainframes; the Toad-1 is a PDP-10 clone system designed and built by engineers long familiar with these systems, running the Tops-20 operating system.

The DEC-10 and DEC-20, as they are familiarly called, are differentiated by the operating systems which run on them, much more than by the hardware attached to them. Tops-10 derives ultimately from the operating system originally created by DEC in 1964 for the PDP-6 system, their first 36-bit computer; it has been since available on all PDP-10 systems built by DEC: The KA-10 system originally sold as the PDP-10; the KI-10 first dubbed the DECsystem-10; the KL-10, created to be the DECSYSTEM-20 but running Tops-10 as well; and the KS-10, a minicomputer implementation of the architecture. All these systems, including the original PDP-6, shared the same user-mode instruction set.

TOPS-20, the operating system for the DEC-20, originated in a operating system called TENEX created by the research firm Bolt, Beranek, and Newman as an experiment in the field of virtual memory computing (a hot topic in the late 1960s). TENEX originated on the KA-10 processor, with paging hardware from BBN which changed the way memory was handled; TENEX was ported to the KI-10 as well. When DEC looked for a way to expand the capabilities of the PDP-10 architecture, TENEX provided a base for their efforts. The new operating system, TOPS-20, was intended to replace Tops-10, but customer requests kept the two systems available to the end of the product's commercial lifetime.

After purchasing the Toad-1, Mr. Allen wanted to acquire a system that could run Tops-10 as well. He first purchased a DECsystem-1090 (a KL-10 processor with external memory), and later acquired a DECSYSTEM-2065 (a KL-10 processor with internal memory) from XKL, which had used it as the testbed for their development of the Toad-1. These systems, along with a number of PDP-8, PDP-11 and VAX-11 minicomputers, comprise the hardware portion of the PDPplanet collection.