David Crystal distinguishes among five areas of the Internet where slang is used- The Web itself, email, asynchronous chat (for example, mailing lists), synchronous chat (for example, Internet Relay Chat), and virtual worlds. The electronic character of the channel has a fundamental influence on the language of the medium. Options for communication are constrained by the nature of the hardware needed in order to gain Internet access. Thus, productive linguistic capacity (the type of information that can be sent) is determined by the preassigned characters on a keyboard, and receptive linguistic capacity (the type of information that can be seen) is determined by the size and configuration of the screen. Additionally, both sender and receiver are constrained linguistically by the properties of the internet software, computer hardware, and networking hardware linking them. Electronic discourse refers to writing that is "very often reads as if it were being spoken – that is, as if the sender were writing talking".