Why is a boolean 1 byte and not 1 bit of size?

Solution 1:

Because the CPU can't address anything smaller than a byte.

Solution 2:

From Wikipedia:

Historically, a byte was the number of bits used to encode a single character of text in a computer and it is for this reason the basic addressable element in many computer architectures.

So byte is the basic addressable unit, below which computer architecture cannot address. And since there doesn't (probably) exist computers which support 4-bit byte, you don't have 4-bit bool etc.

However, if you can design such an architecture which can address 4-bit as basic addressable unit, then you will have bool of size 4-bit then, on that computer only!

Solution 3:

Back in the old days when I had to walk to school in a raging blizzard, uphill both ways, and lunch was whatever animal we could track down in the woods behind the school and kill with our bare hands, computers had much less memory available than today. The first computer I ever used had 6K of RAM. Not 6 megabytes, not 6 gigabytes, 6 kilobytes. In that environment, it made a lot of sense to pack as many booleans into an int as you could, and so we would regularly use operations to take them out and put them in.

Today, when people will mock you for having only 1 GB of RAM, and the only place you could find a hard drive with less than 200 GB is at an antique shop, it's just not worth the trouble to pack bits.