Universal Naming Convention

Universal Naming Convention

UNC paths provide a standardized way of accessing files and devices over a network without specifying or referencing a local drive letter that has been mapped to a remote file system. This is important because it allows applications to become drive-letter–independent and work seamlessly in a network environment. UNC names are better than names that reference a local drive letter because you don't have to worry about running out of drive letters when forming connections to access server shares. Drive letters also operate on a per-user basis—processes that are not running in your user context cannot access your drive mappings.

UNC names are specified as follows:

\\[server]\[share]\[path]

The first portion, \\[server], starts with two backslashes followed by a server name. The server name represents a remote server in which an application wants to reference a remote file. The second portion, \[share], represents a share point on the remote server. A share point is simply a directory in a file system that is identified on a network as shared for network user access. The third portion, \[path], represents a directory path to a file in a file system. For example, suppose you have a server named Myserver that contains a directory on a local drive named D:\Myfiles\CoolMusic that is shared out as Myshare. Let's also assume the shared directory contains a file named SAMPLE.MP3. If you would like to reference SAMPLE.MP3 from a remote machine, simply specify the UNC name \\Myserver\Myshare\Sample.mp3. As you can see, it's much easier to reference a file across a network than it is to map a local drive to the shared directory Myshare.

Referencing files over a network using UNC names hides the details of forming a connection over a network from an application. This is great—a system can easily locate network server directory shares and file paths with UNC names, even over a modem connection. All of the network communication details are handled by a network provider's redirector, which we discuss later in this chapter. As discussed in Chapters 19 and 20, the mailslot and named pipe technologies depend solely on the use of UNC names for identification.

Figure 18-1 illustrates the common components that form UNC connections on the NOS in Windows. The figure also shows how the data flows among client and server NOS components. Using the UNC path \\Myserver\ Myshare\Sample.mp3 described earlier, the remainder of this chapter describes each component and demonstrates what happens when we open this file across a network.

Figure 18-1 Redirector components