Huh? Sometimes C gets in the way of doing that; see below. Alignment is just one aspect of low-level binary representation; there's also length (in bits), which is critically important in several problem domains; device registers have already been mentioned, but more below. That's yet another one. The area I'm thinking of (and which I saw a lot of) is code to implement network protocols (and I'm fairly astounded that nobody else has mentioned this yet). One has to have _absolute_ control over how the bits are laid out in the packet (which of course might wind up in any one of countless other machine types) - which generally means how they are laid out in memory. The whole concept of C declarations is not rich enough to really deal with this properly. For each field in the header, one absolutely needs to be able to separately specify the syntax (e.g. size in bits) and semantics (unsigned integer, etc). And if you want the code to be portable, so that one set of sources will compile to working code on several different architctures, it gets worse. Device registers, already mentioned, often only have to run on one type of machine, but having protocol implementions run on a number of different machine types is really common. I came up with a way to do this, without _any_ #ifdefs (which I don't like, for a reason I won't get into) in most source files. Dealing with byte order issues was similarly dealt with (one can't deal with it just in types, really, without making the type specification, and the language, somewhat complicated). I know later C's got better about richer variable semantics and syntax selection than the circa 1985 ones I was working with, but I don't think it was ever made completely simple and orthogonal (e.g. 'signed/unsigned/boolean/etc char/short/long/quad/word/etc') as it should have been. Noel