Forth Generation

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.