Protocol Prefixes :// and :/

[Ken VdB]

Hi everyone,

I have a strange question that I cant find the answer to anywhere on the
web. Why do some protocols, such as HTTP, use a :// in their prefix while
others use just :/ (such as SMB)? There are still other protocols that use
just the : character such as telnet.

http://myhost.com
smb:/samehost.com
-or-
telnet:samehostagain.com

Does anyone know the history behind this and/or the reason for it?

Thanks,

Ken.