[comex]

"Word" only means 16 bits on x86; on 32-bit ARM, for example, it means 32 bits, and the architecture manual uses "doubleword" to refer to 64 bits. [edit: the parent's post was edited but originally asked about this]

Having int be 64-bits is known as ILP64 (int, long, and pointers 64-bit); some obscure systems handled the 64-bit transition that way (Cray), but Unix went with LP64 (long and pointers 64-bit), and Windows went with LLP64 (long long and pointers 64-bit). Here's an interesting document from 1997 comparing the approaches:

http://www.unix.org/version2/whatsnew/lp64_wp.html

Basically a matter of tradeoffs around compatibility, performance, and consistency.

[api]

Use "stdint.h" in all new code. I only use 'int' and 'long' for counters I know won't be that big, etc. I use stdint types for anything where I might care about the size.