A modem is used to link a computer to the telephone system, allowing data to be transferred to it and from it and thus to be sent and received. A modem can be internal (part of the "box" part of the computer) or external (linked to the central processing unit by a lead).

Dr Ju Gosling aka ju90's ABNORMAL: How Britain became body dysphoric and the key to a cure is available now for just £3.09 for the Kindle or in a limited-edition hardback with full-colour art plates for £20 inc UK postage and packing. Book cover