Computers communicate in numbers . In texts , each number will be translated to a corresponding letter. The meaning that will be assigned to a certain number depends on the character set (charset) that is used.
A charset can be seen as a table that is used to translate numbers to letters . Not all computers use the same charset (there are charsets with German umlauts, Japanese characters, and so on). The American Standard Code for Information Interchange (ASCII) encoding system has been the normative character encoding scheme used by computers to date. This employes a charset that contains 256 characters . Using this mode of encoding each character takes exactly one byte.
There are also charsets that support extended characters, but those need at least twice as much storage space as does ASCII encoding. Such charsets can contain 256 * 256 = 65536 characters, which is more than all possible characters one could think of. They are called multibyte charsets because they use more then one byte to store one character.
One standardized multibyte charset encoding scheme is known as unicode  . A big advantage of using a multibyte charset is that you only need one. There is no need to make sure two computers use the same charset when they are communicating.
Old Windows clients use single-byte charsets, named codepages , by Microsoft. However, there is no support for negotiating the charset to be used in the SMB/CIFS protocol. Thus, you have to make sure you are using the same charset when talking to an older client. Newer clients (Windows NT, 200x, XP) talk unicode over the wire.