A computer modem's rating of 56 K refers to its-

The correct answer is D, Transmission speed. The 56 K rating of a modem means it can transfer data at up to 56 kilobits per second, so the figure describes speed, not size. A modem, short for modulator-demodulator, converts the computer's digital signals into analogue form for a telephone line and converts incoming analogue signals back into digital form. Data transfer speed is measured in bits per second and its multiples, kbps, Mbps and Gbps, and the 56 kbps dial-up modem was the fastest standard for ordinary telephone lines before broadband. A is wrong because the physical size of a modem is not rated in kilobits. B is wrong because memory size is measured in bytes such as MB or GB, not in K of this kind. C is wrong because capacity here is loosely worded; the rating fixes the rate of transfer per second. Exam tip: modem speed is in bits per second; storage is in bytes.