Based on a virtual machine, the UCSD p-system is a portable microcomputer operating system used in the late 1970s and early 1980s. It has certain similarities with Java; for example, both UCSD p-system and Java write programs in pseudocode that are transferable to other platforms with virtually no necessary modifications. The UCSD p-system was developed under Kenneth Bowles, who worked at the Institute for Information Studies at the University of California- San Diego. The Pascal language was primarily used in p-systems, and was compiled into "p-code," to be read as instructions by the virtual machine.