VLSI technology of IC made it possible to design the complete circuit of ALU Arithmetic logic unit and cu ( Control Unit ) within single chip which comprises teh main proc3essing part called central processing unit (CPU) of computer systems see this chip was named microprocessor. The main different between third & forth generation is the invention of microprocessor ( Processor on single chip) although in both generation technology of IC issued. We identify the microprocessor by a chip number given to the it. Since it is the most important part of a computer system we identify the whole computer system by that chip number of the microprocessor. For example we usually say that we are working on 80386, 80486 or Pentium ( 80586) computer. Actually these are the number given by the microprocessor used inside that computer.
Intel 4004 (first 4 bit microprocessor ) Intel 8008 ( 8 - bit processor ) Intel 8080 Zilog Z 80 and Motorola 6800 were few early microprocessor of this generation which had the features of addressing mode and instruction type. Due to very fast growth in the technology and demand a series of microprocessors were invented in a very short period like Intel 8085,8088,8016,80286,80386,80486,then Pentium ( 805686).
Figure Basic Block Diagram of Computer Systems
Here are the main features of various Intel processor:
8085 : 8 bit processor 8 bit data bus 8 bit general purpose register 16 bit address bus which can access 64 K of memory simple architecture.
8086 : 16 bit processor 16 bit data bus 16 bit general purpose registers 20 bit address bus which can address 1MB of memory first member of 80 x 86 family concept of segmented memory new instruction set supported by all upcoming processor of the family of 80 x 86 .
80286 : Similar to 8086 except it has 8 bit address bus which can address 16 MB of storage new memory management provides virtual storage space of 1GB allows larger program to run operates in two addition of new registers.
80386: 32 bit processor with data bus of 32 bit address but 32 bit capable of accessing 4GB of physical memory and over 64 trillion bytes of virtual storage general purpose resisters are extended to 32 bit with addition of new registers.
80486 : Similar features as 80386 with a new feature of cache memory internal architecture redesigned which reduces the execution time of same in structions of 80386 has on chip co processor earlier external co processor was required.
Pentium : 63 bit processor with 64 bit data bus 32 bit address bus it is a mixture of CISC ( Complex instruction set computer) and RISC ( Reduced Instruction Set Computer ) has separate 8 KB data and instruction cache dual integer pipelines and prediction.