The size and speed of computers have changed dramatically since the development of the first general purpose electronic digital computer--the ENIAC. （1）.   in 1946, the massive computer could perform about 5,000 additions and 1,000 multiplications per second. Early computers like ENIAC used bulky, unreliable vacuum tubes. The （2）.   of the transistor in 1947 led to the production of faster, smaller, and more reliable electronic computers. Development of the integrated circuit in the （3）.   1960's continued the miniaturization process. Many of today's integrated circuits contain millions of transistors and other tiny parts on a small chip. Smaller and less （4）.   components made the development of smaller computers -- called personal computers -- possible. Today's personal computers are more powerful than the room-sized computers of the past, and are capable of carrying out millions of instructions per （5）.   . Small, portable notebook computers usually weigh less than five pounds, and powerful palm top computers weigh even less.