Some people mean by that that
wine must emulate each processor instruction of the Windows application. This is plain wrong. As
wine's name says: "
wine Is Not an Emulator":
wine does not emulate the Intel x86 processor. It will thus not be as slow as Wabi which, since it is not running on a x86 Intel processor, also has to emulate the processor. Windows applications that do not make system calls will run just as fast as on Windows (no more no less).
Some people argue that since
wine introduces an extra layer above the system a Windows application will run slowly. It is true that, in theory, Windows applications that run in
wine or are recompiled with Winelib will not be able to achieve the same performance as native Unix applications. But that's theory. In practice you will find that a well written Windows application can beat a badly written Unix application at any time. The efficiency of the algorithms used by the application will have a greater impact on its performance than
wine.
Also, and that's what people are usually interested in, the combination
wine+Unix may be more efficient that Windows. Just as before it's just how good/bad their respective algorithms are. Now to be frank, performance is not yet a
wine priority. Getting more applications to actually work in
wine is much more important right now. For instance most benchmarks do not work yet in
wine and getting them to work at all should obviously have a higher priority than getting them to perform well.
But for those applications that do work and from a purely subjective point of view, performance is good. There is no obvious performance loss, except for some slow graphics due to unoptimized
wine code and X11 driver translation performance loss (which can be a problem sometimes, though).
