Explain binary coded decimal?

BCD uses binary digits as if they were decimal digits. There are two BCD numbers per one 8-bit byte. For example, 23 decimal would be coded as 0010 0011, while in binary (not BDC), it would be 0001 0111. Similarly, 255 in BCD is 0000 0010 0101 0101, while in binary, it would b simply 1111 1111. As you can see, BCD is not as compact as binary, but it does have mathematical and software properties that makes it desirable (some games use BDC to store a "score", for example, because it takes fewer CPU cycles to display a BCD than a binary number).