Distributed shared memory (DSM) is a service an operating system can provide to make a collection of computers interconnected by a communications network appear at the applications level like a shared-memory multiprocessor. In this talk, I will describe a distributed shared memory facility I designed and implemented for the FreeBSD operating system (a 4.4BSD derivative that runs on the Intel x86 architecture). I will discuss how I used a user-level server together with the the "shadow chain" and "external pager" features of the Mach virtual memory system (which is used in FreeBSD) to minimize the intrusion of the DSM facility on the rest of the operating system. I will also discuss interesting issues that arose in the design of the coherence protocol. I will conclude by discussing the current status of the implementation and mention possibilities for further work.