Small virtual machines: A survey

It has been demonstrated that virtual machines can be successfully implemented on large computer systems. They can also be implemented on small computer systems (“mini-computers”). The paper will show this, and at the same time discuss the various architectural features by which virtual machine implementation is achieved. Examining features which make machines “small”, we find architectural limitations. These machines are usually byte or word addressable where the virtual address space bound is the word size. They usually rely on indexing and indirect addressing. Most instructions are one word long. The instruction repetoire is not particularly rich. There is a simple I/O structure with facilities for hardware interrupts and direct memory access (block I/O transfers). In summary, small virtual machines are effective for software development of systems having one or more of the following characteristics: • shared facilities • no common operating system • user I/O programming •communications control •process control •fictitious I/O devices