When FTP was designed, insufficient work had been done on file system models to allow all file systems to be mapped onto a common data model. Therefore, the protocol is not completely opaque and allows -- indeed, requires -- the client to be aware of the type of system to which it connects. Within the unix world, this is not a problem, but a unix person confronting a non-unix system is frequently puzzled by a non-standard syntax for filenames, or non-hierarchical directory system.
To solve this problem and a few others, the world-wide web had to define a new protocol, HTTP. When making pointers to FTP archives, WWW clients (except the very smartest) typically assume that the system is unix or unix-like.
The WWW address for an FTP file consists of a concatenation of the host name (with optional username and password, not normally used) and the filename, in unix-style syntax.
ftp://ftp.w3.org/pub/www/doc(up to existing schemes , on to news ) Tim BL