A PC with a 486DX2 processor runs internally at 50Mhz. What speed would its external logic be running?

ANS:B - 25Mhz

The number of bits processed at one time is the processor's register size (word size). Intel's 8086 processor's register size is 16 bits, or 2 bytes. Today's CPUs have register sizes of 64 or 128 bits.
Buses

Processors operate on 1s and 0s. Processors operate on 1s and 0s. The 1s and 0s must travel from one place to another inside the processor, as well as outside to other chips. To move the 1s and 0s around, electronic lines called a bus are used. The electronic lines inside the CPU are known as the internal data bus or system bus. In the 8086, the internal data bus comprises 16 separate lines, with each line carrying one 1 or one 0. The word size and the number of lines for the internal data bus are equal. The 8086, for example, has a 16-bit word size, and 16 lines carry 16 bits on the internal data bus. In today\'s processors, 64 or 128 internal data bus lines operate concurrently.

For a CPU to communicate with devices in the outside world, such as a printer, the 1s and 0s travel on the external data bus. The external data bus connects the processor to adapters, the keyboard, the mouse, the hard drive, and other devices. An external data bus is also known as an external data path. You can see the external data lines by looking between the expansion slots on the motherboard. Some solder lines between the expansion slots are used to send data out along the external data bus to the expansion slots. Today\'s processors have 64- and 128-bit external data paths. Figure 3.3 shows the internal and external data buses.