JOS is a Unix-based operating system and has Unix-like functions (e.g., fork, exec), but is implemented in an exokernel style (i.e., the Unix functions are implemented mostly as user-level library instead of built-in to the kernel). The major parts of the JOS operating system are:

Booting

Memory management

User environments

Preemptive multitasking

File system, spawn, and shell

Network driver

JOS operating system is developed for a standard x86-based personal computer (32-bit). The OS can be simulated using complete machine simulator (QEMU).