Virtual Machines• Software emulation of an abstract machine
– Make it look like hardware has features you want
– Programs from one hardware & OS on another one
• Programming simplicity
– Each process thinks it has all memory/CPU time
– Each process thinks it owns all devices
– Different Devices appear to have same interface
– Device Interfaces more powerful than raw hardware
• Bitmapped display windowing system
• Ethernet card reliable, ordered, networking (TCP/IP)
• Fault Isolation
– Processes unable to directly impact other processes
– Bugs cannot crash whole machine
• Protection and Portability
– Java interface safe and stable across many platforms
Virtual Machines :Layers of OSs
• Useful for OS development
– When OS crashes, restricted to one VM
– Can aid testing programs on other OSs