1、Microprocessors A microprocessor is a computation engine that is fabricated on a single chip. The first microprocessor was the Intel 4004, introduced in 1971 .The 4004 was not very powerful all it could do was add and subtract, and it could only do that 4 bits at a time. But it was amazing that ever
2、ything was on one chip. Prior to the 4004, engineers built computers either from collections of chips or from discrete components. The 4004 powered one of the first portable electronic calculators. The first microprocessor to make it into a home computer was the Intel 8080, a complete 8-bit computer
3、 on the chip, introduced in 1974. The first microprocessor to make a real splash in the market was the Intel 8088 , introduced in 1979 and incorporated into the IBM PC. The PC market moved from the 8088 to the 80286 to the 80386 to the 80486 to the Pentium to the Pentium II to the Pentium III to the
4、 Pentium 4. All of these microprocessors are made by Intel and all of them are improvements on the basic design of the 8088. The Pentium 4 can execute any piece of code that ran on the original 8088, but it does it about 5,000 times faster! The following table shows the differences between the diffe
5、rent processors that Intel has introduced over the years. Table1.2 Name Date Transistors Micron1 Clock speed Data width2 MIPS3 8080 1974 6,000 6 2 MHz 8 bits 0.64 8088 1979 29,000 3 5 MHz 16 bits 8-bit bus 0.33 80286 1982 134,000 1.5 6 MHz 16 bits 1 80386 1985 275,000 1.5 16 MHz 32 bits 5 80486 1989
6、 1,200,000 1 25 MHz 32 bits 20 Pentium 1993 3,100,000 0.8 60 MHz 32 bits 64-bit bus 100 Pentium II 1997 7,500,000 0.35 233 MHz 32 bits 64-bit bus 300 Pentium III 1999 9,500,000 0.25 450 MHz 32 bits 64-bit bus 510 Pentium 4 2000 42,000,000 0.18 1.5 GHz 32 bits 64-bit bus 1,700 From this table you can
7、 see that, in general, there is a relationship between clock speed and MIPS. The maximum clock speed is a function of the manufacturing process and delays within the chip. There is also a relationship between the number of transistors and MIPS. For example, the 8088 clocked at 5 MHz but only execute
8、d at 0.33 MIPS(about one instruction per 15 clock cycles). Modern processors can often execute at a rate of two instructions per clock cycle. That improvement is directly related to the number of transistors on the chip. Inside a Microprocessor A microprocessor executes a collection of machine instr
9、uctions that tell the processor what to do. Based on the instruction, a microprocessor does three basic things: 1. Using its ALU (Arithmetic/Logic Unit), a microprocessor can perform mathematical operations like addition, subtraction, multiplication and division. Modern Microprocessors contain compl
10、ete floating point processors that can perform extremely sophisticated operations on large floating point numbers. 2. A microprocessor can move data from one memory location to another. 3. A microprocessor can make decisions and jump to a new set of instructions based on those decisions. These may b
11、e very sophisticated things that a microprocessor does, but those are its three basic activities. The following diagram shows an extremely simple microprocessor capable of doing those three things: This microprocessor has an address bus that sends an address to memory, a data bus that can send data
12、to memory or receive data from memory, an RD (read) and WR (write) line to tell the memory whether it wants to set or get the addressed location, a clock line that lets a clock pulse sequence the processor and a reset4 line that resets the program counter to zero (or whatever) and restarts execution. And lets assume that both the address and data buses are 8 bits wide here. Here are the components of this simple microprocessor (Figure 1.1):
