A BUS "only" a collection of parallel wires or tracks which holds a digital value 0/1 or they could be undefined (not driven)

The last state called Z or the high impedance state

More elements which present in a PC

•  Instruction set:
  •  A collection of simple commands which the CPU "born" with
  •  Transfer instructions for moving data between registers and the I/O
  •  Arithmetic instructions for addition, subtraction, multiplication and division available.
  •  Logic instructions like AND, OR, NOT, COM and XOR handy as well.
  •  Branch and Jump instructions makes it possible for a program to make decisions
  •  The internal CPU control also needed for a programmer.

•  Addressing of memory and IO:
  •  Direct makes it possible to access a specific memorycell
  •  Immediate made for loading constants into registers
  •  Register indirect makes it possible to perform calculation at a address at runtime
  • .Inherent for moving data between registers.
  •  Input / Output for reaching the IO-Space

•  Operating system: (Link to timeline)
  •  The first version for PCs was DOS, CP/M-86, OS2
  •  Now the most popular Windows and Linux
  •  A OS enable the user to start and stop programs
  •  The OS performs multitasking (more the one program running at the same time)
  •  Manage the file-system.
  •  Enables net-working.

•  Applications:
  •  99% of PC uses doesn't have worries about the internal of their PC's such as hardware structure and assembler programming.
    (The same true for car-owners - they just hit the road)
  •  Word processing, Browsers and Games popular applications.
  •  With a compiler for high level languages like: C, C++ C#, Java, Delphi, Visual Basic and so on .. will it be possible to write programs for a PC without detailed knowledge of the internal. (Link to timeline )

•  Conclusion:
  •  PC's by nature "general purpose"
  •  Its possible to buy PC's for harsh environments.
  •  Special applications programs for PC's makes them act like PLC's (Search for more information about SoftPLCs yourself)
  •  Programming of a PC not and easy task if you must work with the hardware in order to get input/output.