Portable Distributed Objects

Portable Distributed Objects, or PDO, is a programming API for creating object-oriented code that can be executed remotely on a network of computers. It was created by NeXT Computer, Inc. using their OpenStep system, whose use of Objective-C made the package very easy to write. It was characterized by its very light weight and high speed in comparison to similar systems such as CORBA.

Versions of PDO were available for Solaris, HP-UX and all versions of the OPENSTEP system. A version that worked with Microsoft OLE was also available called D'OLE,^[1] allowing distributed code written using PDO on any platform to be presented on Microsoft systems as if they were local OLE objects.

PDO was one of a number of distributed object systems created in the early 1990s, a design model where "front end" applications on GUI-based microcomputers would call code running on mainframe and minicomputers for their processing and data storage. Microsoft was evolving OLE into the Component Object Model (COM) and a similar distributed version called DCOM,^{[citation needed]} IBM had their System Object Model (SOM/DSOM), Sun Microsystems was promoting their Distributed Objects Everywhere, and there were a host of smaller players as well. With the exception of the limited functionality in COM,^{[citation needed]} most of these systems were extremely heavyweight, tended to be very large and slow, and often were very difficult to use.