1. bytes are 8 bits
2. shorts are 16 bits
3. ints are 32 bits
4. longs are 64 bits
5. arithmetic is 2's complement
6. IEEE floating point
and a big chunk of wasted time trying to abstract these away and getting it wrong anyway was saved. Millions of people cried out in relief!
Oh, and Unicode was the character set. Not EBCDIC, RADIX-50, etc.
1. char 8 bit
2. short 16 bit
3. int 32 bit
4. long long 64 bit
5. arithmetic is 2s complement
6. IEEE floating point (float is 32, double is 64 bit)
Along with other stuff like little endian, etc.
Some people just mistakenly think they can't rely on such stuff, because it isn't in the standard. But they forget that having an ISO standard comes on top of what most other languages have, which rely solely on the documentation.
That's the problem
In C, the ISO standard is the authority on how you're supposed to write your code for it to be "correct C". The compiler implementors write their compilers against the ISO standard. That standard is not clear on these things.