Named pipes and mailslots are actually written as file systems, unlike other IPC mechanisms. Thus, the Registry lists entries for the Named Pipes File System (NPFS) and the Mailslot File System (MSFS). As file systems they share common functionality, such as caching, with the other file systems. Additionally, processes on the local computer can use named pipes and mailslots to communicate with one another without going through networking components. Remote access to named pipes and mailslots, as with all of the file systems, is provided through the redirector.
Named pipes are based on OS/2 API calls, but in Windows NT they include additional asynchronous support and increased security.
Another new feature added to named pipes is impersonation, which allows a server to change its security identifier so that it matches the client's. For example, suppose a database server system uses named pipes to receive read and write requests from clients. When a request comes in, the database server program can impersonate the client before attempting to perform the request. So even if the server program does have authority to perform the function, the client may not, and the request would be denied. (For more information on impersonation, see Chapter 2, "Windows NT Security Model" of the Windows NT Resource Guide.)
Mailslot APIs in Windows NT are a subset of those in Microsoft OS/2 LAN Manager. Windows NT implements only second-class mailslots, not first-class mailslots. Second-class mailslots provide connectionless messaging for broadcast messages and so on. Delivery of the message is not guaranteed, although the delivery rate on most networks is very high. Second-class mailslots are most useful for identifying other computers or services on a network and for wide-scale notification of a service.