simulators versus emulators

[steve marchant]

Having difficulty with seeing any difference between the two terms.Can
anyone offer definitions, both generally and in relation to, say,
microprocessors.

 

[Don Taylor]

"steve marchant" <steve.c.marchant@btopenworld.com> writes:

Having difficulty with seeing any difference between the two terms.Can
anyone offer definitions, both generally and in relation to, say,
microprocessors.

A simulator is usually a software model of hardware running a program.

An emulator is usually a hardware model of hardware running a program.

A software model can assume, for example, that you have a good clock
signal getting to the processor. It can assume that any input logic
levels have sufficient voltage and current, don't bounce, all the
usual things you might assume to be true. The free PIC simulator
provided by Microchip is a good example. It assumes a variety of
things and your code can seem to run fine. Then when you toast a
part and drop it into your board it doesn't run, because one of those
assumptions wasn't valid.

Software models may also run at a tiny fraction of the real speed
of the actual hardware, but this doesn't always have to be the case.
That can cause grief when you are attempting to deal with real-time
signals, timing constraints, interrupts that must be serviced in
a fixed small amount of time, etc.

A hardware model should act exactly like your real hardware processor
does. In reality there can be tiny differences there too. But it
usually is able to run at full speed and deal with more of the ugly
reality of the signals that you are connecting directly to the
hardware. But by being built out of more complicated hardware than
the bare processor it can also allow you to set breakpoints, record
execution for hundreds or even millions of clock cycles, observe
internal processor state, all without your needing to have your
program be modified to attempt to provide this.

 

[Martin Blume]

"steve marchant" schrieb

Having difficulty with seeing any difference between
the two terms.Can anyone offer definitions, both
generally and in relation to, say, microprocessors.

http://dictionary.reference.com/search?q=emulator
tells me (among other definitions):

Computer Science. To imitate the function of (another system), as by
modifications to hardware or software that allow the imitating
system to accept the same data, execute the same programs, and
achieve the same results as the imitated system.

whereas the search for simulator returns:

One that simulates, especially an apparatus that generates test
conditions approximating actual or operational conditions.


For me, the important thing that the emulator tries to
have the same usefulnesss to an user as the "real" thing.

For example, think of a terminal that ***emulates*** a
VT-100 terminal. Nobody has a VT-100 simulator.

HTH
Martin