Update

portability.md

@@ -8,7 +8,7 @@ In connection to software the word *portable* also has one other meaning used ma
 
 ## How To Make Portable Programs
 
-In short: use [abstraction](abstraction.md) to not get tied to any specific platform (separate [frontend](frontend.md) and [backend](backend.md)), [keep it simple](kiss.md), minimize [dependencies](dependency.md) (minimize use of [libraries](library.md) and requiring hardware such as [floating point](float.md) unit or a [GPU](gpu.md), have [fallbacks](fallback.md)), write efficient, [simple](kiss.md) code (lower hardware demands will support more platforms), avoid platform-specific features (don't write in [assembly](assembly.md) as that's specific to each CPU, don't directly use [Linux](linux.md) [syscalls](syscall.md) as these are specific to Linux etc.).
+In short: use **[abstraction](abstraction.md)** (only necessarily small amount) to not get tied to any specific platform (separate [frontend](frontend.md) and [backend](backend.md)), **[keep it simple](kiss.md)**, **minimize [dependencies](dependency.md)** (minimize use of [libraries](library.md) and requiring hardware such as [floating point](float.md) unit or a [GPU](gpu.md), have [fallbacks](fallback.md)), write efficient, [simple](kiss.md) code (lower hardware demands will support more platforms), avoid platform-specific features (don't write in [assembly](assembly.md) as that's specific to each CPU, don't directly use [Linux](linux.md) [syscalls](syscall.md) as these are specific to Linux etc.). Also use **[self hosting](self_hosting.md)** (i.e. write your programming language in itself etc.) to make your program self contained and minimize dependencies on anything external.
 
 Remember, portability is about **making it easy for a programmer to take your program and make it run elsewhere**, so portability is kind of a mindset, it is about constantly putting oneself in the shoes of someone else with a very different computer and asking questions such as "how hard will it be to make this work if this library isn't available?". Even things that are supposed or commonly expected to be present on all platforms, such as a file system or a raster screen, may not be present on some computers -- always remember this.
 
@@ -164,3 +164,4 @@ You'll get the SDL version.
 
 A great example of this kind of portable design can be seen e.g. in well written **[compilers](compiler.md)** that separate their architecture into an frontend and backend -- imagine we are writing for example a [C](c.md) compiler. The parser of C syntax can be easily written in a portable way, we simply write functions that work with text, however we find difficulty in asking what [instruction set](isa.md) we will compile to. If we choose one, such as [x86](x86.md), then we will not only write an x86 specific code generator, but also e.g. an x86 specific [optimizer](optimization.md); the part of the compiler that may get so complex that it ends up being bigger than the rest of the code. What if then we also want to support another ISA such as [Arm](arm.md) or [RISC-V](risc_v.md), will we have to rewrite our painstakingly written optimizer for those architectures from scratch? The solution is the same as explained above in regards to I/O: we make an abstraction above the instruction set, here called an [intermediate representation](intermediate_representation.md), usually some [bytecode](bytecode.md), i.e. the compiler first translates C to the abstract bytecode, then we may perform all the complex optimizations on this bytecode, and only then, in the last moment, we relatively simply translate this bytecode to whatever specific instruction set.
 
+Programming languages, operating systems and other "platforms" also usually employ [self hosting](self_hosting.md) to greatly increase portability -- you will most often see a serious programming language written in itself and if not, then at very least e.g. its standard library will be written as such. See also [bootstrapping](bootstrapping.md).