Windows Username maximum length

Read this

for windows 2000: http://technet.microsoft.com/it-it/library/bb726984(en-us).aspx

for windows 2003: http://technet.microsoft.com/en-us/library/cc783323.aspx

Rules for Logon Names

Logon names must follow these rules:

• Local logon names must be unique on a workstation and global logon names must be unique throughout a domain.
• Logon names can be up to 104 characters. However, it isn't practical to use logon names that are longer than 64 characters.
• A Microsoft Windows NT version 4.0 or earlier logon name is given to all accounts, which by default is set to the first 20 characters of the Windows 2000 logon name. The Windows NT version 4.0 or earlier logon name must be unique throughout a domain.
• Users logging on to the domain from Windows 2000 computers can use their Windows 2000 logon name or their Windows NT version 4.0 or earlier logon name, regardless of the domain operations mode.

The maximum lengths are hash defined in lmcons.h. DNLEN is the maximum domain length and UNLEN is the maximum user name length.

In the version of this file I have on my XP machine (installed as part of Visual Studio 8), DNLEN = 15 and UNLEN = 256.

There is a constant UNLEN which is defined in Lmcons.h that defines the maximum length of a username