C code would be just as fast as assembly if you
Assembler code is usually much faster if you do like this:
C code is usually more portable than assembler if any of this holds:
It will be both faster and smaller. This is significant for all parts of an OS. Some say you don't need to optimize the file-system since the disk-drives are slow anyway. Well, that's not true, since many of the requests for files will be read from buffers. Many portable, C based OSes have a very slow file-system, and it's not because the disk-drives are slow, it's because the C code and all the layering. File-system performance is actually one of the most critical parameters in an OS!