4D uses an Extended ASCII encoding referred to as "Mac OS Roman" or "MacRoman" for short. When data is entered on a Windows machine it is converted to MacRoman encoding for storage in the database. Note that this is transparent to the user. You can find more information (including the character tables) here:
It is important to note that true ASCII only defines the first 128 characters for a 7-bit range (from 0 to 127).
The term "Extended ASCII" is often used to refer to a specific character encoding but this is not really what it means. There are many 8-bit character encodings that define what characters are represented by the additional 128 characters, going from 128 to 255. All of these encodings might generically be called Extended ASCII but Extended ASCII is not a single encoding.
Apple defined the MacRoman extended ASCII character encoding that 4D uses internally.