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 processor architectures, because real hardware was not available to us. Using virtual environment
 for developing our system provided us with deterministic environment on which it is much easier to do
 troubleshooting. Moreover, part of the simulators featured integrated debugging facilities.
 Without them, a lot of bugs would remain unresolved or even go unnoticed.
+Using several virtual environments for testing one architecture is well justified by the
+fact that sometimes HelenOS would run on two and crash on third or vice versa. Sometimes
+we found that it runs on real hardware but fails in a simulator. The opposite case was,
+however, more common. Simply put, the more configurations, no matter whether real or virtual,
+the better.
 From one point of view, we have tested our system on eight different virtual environments:
 \begin{itemize}
 \item Bochs,
 \item GXemul,
 Our project has not only used Bochs. We also helped to identify some SMP related problems
 and {\OP} from our team has discovered and also fixed a bug in FXSAVE and FXRSTOR emulation
 (patch \#1282033).
 Bochs has some debugging facilities but those have been very impractical and broken
+in SMP mode. Moreover, it is possible to use the GNU debugger {\tt gbd} to connect to running
+simulation, but this has also proven not very useful as we often needed to debug
+problems that existed only in multiprocessor configurations, which {\tt gdb}
-in SMP mode.
+does not understand.
 \subsection{GXemul}
 GXemul is an emulator of several processor architectures. Nevertheless, we have
 used it only for mips32 emulation in both little-endian and big-endian modes.
 It seems to be pretty featurefull and evolving but we don't use all its functionality.
 This emulator seemed to realistically emulate the {\tt hlt} instruction,
 which was nice for those of us who use notebooks as their development
 machine.
+Similar to Bochs, QEMU simulation can be aided by {\tt gdb}. Debugging
+with {\tt gdb} can be pretty comfortable\footnote{Especially when the kernel is
+compiled with {\tt -g3}.} until one needs to debug a SMP kernel running on multiple
+processors.
 \subsection{Simics}
 Virtutech's Simics simulator can be compared to a Swiss-army knife for operating system debugging.
 This proprietary piece of software was available to us under an academic license for free.
 Simics can be set to simulate many different configurations of many different machines.
 that Ski confuses VMA and LMA. This, what we believe to be a bug in Ski, has not shown in Linux since Linux always has
 LMA equal to VMA. People from the Ski mailing list had tried to help us but our repeated problem report didn't
 make it far enough for the HP to fix or at least clarify the issue. Finally, we adopted a workaround implemented by {\JJ}
 that simply swaps LMA and the program entry point in the kernel ELF image.
-\subsection{VMware}
+\subsection{VMware} VMware is the only virtualizer we have used in
-VMware is the only virtualizer we have used in HelenOS development. It virtualizes the ia32 host machine.
+HelenOS development. It virtualizes the ia32 host machine. Since VMware
-Since VMware version 5.5, we made use of its possibility to run the guest system (i.e. HelenOS) on multiple processors.
+version 5.5, we made use of its possibility to run the guest system
+(i.e. HelenOS) on multiple processors. VMware has no support for
-VMware has no support for debugging but is very useful for compatibility and regression testing because
+debugging but is very useful for compatibility and regression testing
-it's closest to the real hardware. VMware, being a virtualizer, is also the fastest of all the virtual environments
+because it's closest to the real hardware. VMware, being a virtualizer,
-we have utilized.
+is also the fastest of all the virtual environments we have utilized.
-\section{Authoring tools}

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