Students' Guide to Information Technology, 2nd Edition

Computers

of the other components. So replacing an 8086 processor in an old

PC by an 80386 processor does not mean that the PC will be able to

run at 20 or

25

MHz.

The original IBM PC with its 8086 chip supported a clock speed

of 4.77 MHz. To execute the average instruction required about 15

clock cycles, so its processing speed was 0.3

MIPS.

The latest PCs

using the 80486 chip have clock speeds of 30 or 35 MHz and execute

an instruction in just over 2 clock cycles, giving a processing speed

of around

15

MIPS.

The i860 RISC chip has a clock speed of around

40 MHz and executes about 1 instruction per clock cycle, giving a

processing speed o