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The first version of UNIX to include `calloc` was Research UNIX V6, and here's how it was implemented: https://github.com/dspinellis/unix-history-repo/blob/Researc...
calloc(n, s)
{
return(alloc(n*s));
}
- `calloc` originated not on UNIX, but as part of Mike Lesk's "iolib", which was written to make it easier to write C programs portable across PDP 11 UNIX, Honeywell 6000 GCOS, and IBM 370 OS[0]. Presumably the reason calloc is the-way-it-is is hidden in the history of the implementation for GCOS or IBM 370 OS, not UNIX. Unfortunately, I can't seem to track down a copy of Bell Labs "Computing Science Technical Report #31", which seems to be the appropriate reference.
- `calloc` predates `malloc`. As you can see in the above code, there was a `malloc`-like function called just `alloc` (though there were also several other functions named `alloc` that allocated things other than memory). (Ok, fine, since V5 the kernel's internal memory allocator happened to be named `malloc`, but it worked differently[1]).
[0]: https://github.com/dspinellis/unix-history-repo/blob/Researc... (format with `nroff -ms usr/doc/iolib/iolib`)
[1]: https://github.com/dspinellis/unix-history-repo/blob/Researc...