字节是计算机中数字数据存储的较小单位。在计算机中，RAM有数百万个字节，每个字节都有一个地址。如果每个比特都有一个地址，那么计算机就可以少管理8倍的内存。

更多信息:维基百科

您可以使用位字段来获取子大小的整数。

struct X
{
    int   val:4;   // 4 bit int.
};

尽管它通常用于将结构映射到精确的硬件预期位模式:

// 1 byte value (on a system where 8 bits is a byte)
struct SomThing   
{
    int   p1:4;   // 4 bit field
    int   p2:3;   // 3 bit field
    int   p3:1;   // 1 bit
};

因为CPU不能寻址任何小于字节的东西。

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.

今天，当人们嘲笑你只有1gb的RAM，而你唯一能找到小于200gb的硬盘的地方是在古董店，它只是不值得麻烦打包比特。

最简单的答案是;这是因为CPU以字节而不是位来寻址内存，按位的操作非常慢。

然而，在c++中可以使用位分配。对于位向量，有std::vector专门化，还有接受位大小条目的结构。

即使最小大小可能是1字节，你可以在1字节上有8位布尔信息:

http://en.wikipedia.org/wiki/Bit_array

Julia语言有BitArray，我读过c++实现。