.1 Clients, Servers and Peers 
 The most common categories of network software nowadays are clients and servers .Though this common usage has no detrimental practical effects for 
the majority of I.T. tasks, those I.T. personnel who are unaware of the distinction 
and subsequently undertake network programming are likely to be caused a signifi -
cant amount of conceptual confusion until this distinction is made known to them.(These clients, of course, are also programs and are not human clients!) 
Common services provided by such servers include the 'serving up' of Web pages 
(by Web servers) and the downloading of fi les from servers' host machines via the 
File Transfer Protocol (FTP servers).Indeed, it is often very convenient (as will be 
seen in subsequent chapters) for server and client(s) to be run on the same machine, 
since this provides a very convenient 'sandbox' within which such applications 
may be tested before being released (or, more likely, before fi nal testing on separate machines).In some applications, such as messaging services, it is possible for programs on 
users' machines to communicate directly with each other in what is called peer-topeer (or P2P ) mode.For the former service, the corresponding 
client programs would be Web browsers (such as Firefox, Chrome or Internet 
Explorer).