单选题 Currently the Pentium chip or{{U}} {{U}} 71 {{/U}} {{/U}}, made by{{U}} {{U}} 72 {{/U}} {{/U}}, is the most common CPU though there are many other companies that produce processors for personal computers. One example is the CPU made by Motorola which is used in Apple computers. With faster processors the clock speed becomes more important. Compared to some of the first computers which operated at below 30 megahertz ({{U}} {{U}} 73 {{/U}} {{/U}}) the Pentium chips began at 75 megahertz in the late 1990g. As of mid 2003 speeds now exceed 3000 + megahertz or 3 gigahertz (check your local computer store for the latest speed) . It depends on the{{U}} {{U}} 74 {{/U}} {{/U}}that the chip is housed in, or the{{U}} {{U}} 75 {{/U}} {{/U}}, as to whether you are able to upgrade to a faster chip. The motherboard contains the circuitry and connections that allow the various component to communicate with each other.