单项选择题

Although (21) circuits made computers smaller, the processing units still consisted (22) a number of circuits on separate chips. In 1971, an engineer working for Intel realized that a (23) of circuits commissioned for an electronic calculator could all be put (24) one chip, and that the resulting device could be used (25) a general-purpose "computer on a chip". The result was the Intel 4004 -- the world’s first microprocessor. Physically, it consisted of a silicon chip in a protective ceramic capsule, with a set of metal pins sticking (26) that connected it to other components in whatever (27) it controlled. It (28) 2,300 transistors, (29) 60,000 operations per second, and could be used for any device -- including computers and robots -- that required a "brain" for accepting (30) and following a program of (31) to produce an output. Within five years, many very powerful microprocessors had (32) .The invention of microprocessors (33) the stage for the arrival of the microcomputer, or personal computer (PC)-- an affordable machine for (34) The first PCs, in kit form, appeared in the mid 1970s, and by the mid-1980s machines such as the Apple Macintosh and those based (35) a PC first (36) by IBM in 1981 were popular throughout the world. The success of these machines led to an explosion of software, in (37) a range of spreadsheet, word-processing, graphic, educational, and games programs. Since the 1980s, a number of strong-intertwined themes have (38) the computer revolution forward, including a continuing increase in the processing power and decrease in the size and cost of PCs; a switch of emphasis from (39) to linked machines, as evidenced by the growth of local area networks and the Internet; and the spread of computer applications into virtually every (40) of home and business life.

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