I recently started learning to write code, and in my book I came across this question. "Why is a Boolean value stored as a byte inside of a computer when it only requires one bit?" can someone shed more light on this question?
It has to do with what the CPU can easily address. For example on an x86 processor there is an
eax (32 bits),
ax (16 bits) and a
ah (8 bits) but no single bit register. So in order for it to use a single bit the CPU will have to do a read/modify/write to change the value. If it is stored as a byte a single read or write can be used to inspect/change the value.
Additionally one might wonder if it would be better to use a single bit vs a full byte, after all a byte will be wasting 7 bits. Unless space is a constraint the one should go for the byte because, at least the x86 and I think others, there is usually an instructions to quickly set/clear a bool which is much quicker than the read/modify/write of a single bit. From personal measurements I have seen the read/mod/write method be 5x slower than the single instruction method.
As @barrem23 explains, the data must be addressable, and the smallest boundary on conventional architectures is a byte.
But since this question is tagged as c++, it may be worth pointing out that
std::vector<bool> is specialized to allow individual elements to be stored as bits. This will save space by sacrificing some functionality (for example,
std::search may not work).
It will never be 1 bit, if you group 8 booleans in one byte, you still need 3 bits for each boolean for addressing (2^3 space), that is to know which bit inside the byte belongs to which boolean.
Also you might need one additional bit for nullability checking since you can't have a null bit, so you need one more bit for that, and you end up having 5 bits for each boolean rather than 1 byte (1 for value, 1 for null, and 3 for addressing), which is not that significant optimization.