On Fri, 21 Dec 2001, Paolo Alexis Falcone wrote:
>
> The Java virtual machine is also a good example of a virtual machine.
> Consider the typical compilation-linking process using C. Source code is
> compiled into machine readable object code, afterwhich it is linked to produce
> a binary executable. The object code in itself is tied to the architecture
> (thus OS can only be ported to other architectures once a port of the compiler
> exists for the architecture to be ported to).
>
> For java, source code is compiled into an architecture-independent bytecode,
> which is then interpreted prior to execution. The Java virtual machine acts as
> a virtual hardware, which interacts with low-level, hardware specific routines
> (which is hidden from the user) thus giving the semblance of portability (as
> java bytecode can run on any platform where exists a port of the Java virtual
> machine). The java virtual machine copies the underlying hardware but hides
> it from the user via its interface, thus the illusion of the JVM as a "soft"
> hardware.
One often forgotten system was the UCSD p-System. It executes programs
compiled into a pseudo-code (p-code) which actually makes the binary
portable from one system to another. Quite advance for its time. Never
really took off as during that time it was competing with CP/M. And due
to its interpretive nature, runs slower than other OS.
_
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