MicroprocessorsA 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 everything 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 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 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 different processors that Intel has introduced over the years.Table1.2NameDateTransistorsMicron1ClockspeedData width2MIPS3808019746,00062 MHz8 bits0.648088197929,00035 MHz16 bits8-bit bus0.33802861982134,0001.56 MHz16 bits1803861985275,0001.516 MHz32 bits58048619891,200,000125 MHz32 bits20Pentium19933,100,0000.860 MHz32 bits64-bit bus100Pentium II19977,500,0000.35233 MHz32 bits64-bit bus300Pentium III19999,500,0000.25450 MHz32 bits64-bit bus510Pentium 4200042,000,0000.181.5 GHz32 bits64-bit bus1,700From this table you can 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 executed 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 instructions 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 complete 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 be 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 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):Figure 1.11. Registers A, B and C are simply latches made out of flip flops.2. The address latch is just like registers A, B and C.3. The program counter is a latch with the extra ability to increment by 1 when told to do so, and also to reset to zero when told to do so.4. The ALU could be as simple as an 8 - bit adder, or it might be able to add, subtract, multiply and divide 8 bit values. Lets assume the latter here.5. The test register is a special latch that can hold values from comparisons performed in the ALU. An ALU can normally compare two numbers and determine if they are equal, if one is greater than the other, etc. The test register can also normally hold a carry bit from the last stage of the adder. It stores these values in flip-flops and then the instruction decoder can use the values to make decisions.6. There are six boxes marked “3-State” in the diagram. These are tri-state buffers5. A tri-state buffer can pass a 1, a 0 or it can essentially disconnect its output. A tri-state buffer allows multiple outputs to connect to a wire, but only one of them to actually drive a 1 or a 0 onto the line.