This paper introduces DISK, a distributed Java Virtual Machine for networks of heterogenous workstations. Several research issues are addressed. A novelty of the system is its object-based, multiple-writer memory consistency protocol (OMW). The correctness of the protocol and its Java compliance is demonstrated by comparing the nonoperational definitions of release consistency, the consistency model implemented by OMW, with the Java Virtual Machine memory consistency model (JVMC), as defined in the Java Virtual Machine Specification. An analytical performance model was developed to study and compare the design trade-offs between OMW and the lazy invalidate release consistency (LI) protocols as a function of the number of processors, network characteristics, and application types. The DISK system has been implemented and running on a network of 16 Pentium III computers interconnected by a 100 Mbps Ethernet network. Experiments performed with two applications: parallel matrix multiplication and traveling salesman problem confirm the analytical model.