Writing and maintaining portable software is currently a pain. You need to know properties of each supported platform and write scripts that probe the current platform and configure the build process accordingly. You need to test the code on each of these platforms. When changing code that is low-level enough you need to be extremely careful and do not break the platform dependency code. When looking at the code a couple of years or even only months later you often find yourself lost in the flood of cryptic #if/#ifdef/#else#endif directives and strange macros. People often step back and give up when faced to such a mess. I know it. When I was 18, I wrote a software package contamined with {$IFDEF}/{$ELSE}/{$ENDIF} (it was written in Turbo Pascal and these directives are equivalent to #ifdef/#else/#endif in C). Half of year later I realized that I am not able to work with the code anymore and must rewrite it from scratch or leave it so.
Writing and maintaining cross-buildable software is a hell. The package must hold a database containing information about properties of all supported platforms. This is because the platform the package is build on is not necessarily the one the package will be installed on so no platform probing is possible. This task is often so extremely complicated that almost all large projects are not cross-platform buildable or their cross-platform building capability is restricted. The common restriction is that the target platform (the one for which we build) must have compatible CPU and OS than the host platform (the one on which we build), for example building an 80386 Linux binary on a Pentium Linux box. When the host and target platforms differ substantially (especially when they have different OSes), there is often no possibility to do cross-platform builds.
The OSHS removes all these needs for platform probing, compilation configuring and preprocessor directive pollution coming from the need to have the software portable. All supported platforms are simply required to behave identically. The differences between platforms are deeply burried into the kernel and compiler; so deeply that the only differences that are manifested to the rest of the software world of the OSHS are the differencies in floating point computation results caused by different lengths of the mantissa portions of the floating point registers.
So to port the entire distribution you need to do only these few things: write the OSHS microkernel implementation for the new platform (or port any existing [micro]kernel), write drivers for the platform (or port the existing ones) and instruct the compiler how to call the kernel and how to generate (and possibly optimize) the code for the underlying CPU and (possibly) how to generate the binaries for the platform. Period. Nothing more is required, you do not have to change even a comma in the source code of the remaining software, including the standard OSHS library (!!). After you done all these required things you simply bootstrap the OSHS and voila! The OSHS is suddenly supporting a new platform.
This is so different level of portability that I decided to call it not "portability" but "crossplatformity". I never seen such a level of portability before and I even did not think that this is possible before The Holy Spirit showed me the way how to do this.