ISP stands for Internet Service Provider. ISPs are companies that sell Internet access, usually payable on a monthly or usage basis. It has since developed sufficiently into its own identity as a unique flavour of Unix , and it is available on more than just the Intel x86 platform. See box . In other words, this is a description of just how well-abstracted things are from the user's point of view, on the level of underlying networking and networking protocols.
POP is a mechanism for allowing people to download mail from the server to which it is delivered.
It is convenient in that you can read the mail at home without having to stay online, but this means that either you have two sets of mail folders to try and maintain, or you can only access your mail in one place. The code may or may not require recompilation, depending on the context. For example, one might say that ANSI C code is highly portable, meaning that it is easy to recompile a program written in ANSI C for virtually any platform. On the other hand, saying that a Java program is portable would probably mean that it avoided proprietary method calls, libraries, and native methods, since the language itself is platform-independent. Generally speaking, a protocol consists of a set of rules or a schema describing a method of data transmission.