Multilevel viewpoint of a machine

   


     

 

Level 6: The User Level

•   Program execution and user interface level.
•   The level with which we are most familiar.
•   Composed of application programs such as Word Processor,Paint etc.
•   The implementation of the application is hidden completely from the user

                                         Level 5: High-Level Language Level

•   The level with which we interact when we write programs in languages such as C, Pascal, Lisp,      and Java
•   The level allows users to write their own application with languages such as C, Java and many more
•   High-level languages are easier to read, write, and maintain
•   User at this level sees very little of the lower level

          Level 4: Assembly Language Level

•     Acts upon assembly language produced from Level 5, as well as instructions programmed directly at this level.
•     Lowest human readable form before dealing with 1s and 0s (machine language)
•     Assembler converts assembly to machine language

                                            Level 3: System Software Level

•    Controls executing processes on the system.
•    Protects system resources.
•    Assembly language instructions often pass through Level 3 without modification.
•    Operating System software supervises other programs

             1.   Controls execution of multiple programs

             2.    Protects system resources. E.g. Memory and I/O devices

•    Other utilities

             1.   Compilers, Interpreters, Linkers, Library etc.

•  The software can be written in both assembly and high-level language

              1. High-level is much more portable i.e. easier to modify to work on other machines 

                                                     Level 2: Machine Level

•     Also known as the Instruction Set Architecture (ISA) Level.
•     Consists of instructions that are particular to the architecture of the machine.
•     Programs written in machine language need no compilers, interpreters, or assemblers.
•     Also known as the Instruction Set Architecture (ISA) Level
•     Consists of instructions that are particular to the architecture of the machine
•     Programs written in machine language (0s and 1s) need no compilers, interpreters, or assemblers

                                                     Level 1: Control Level

•     A control unit decodes and executes instructions and moves data through the system.
•     Control units can be microprogrammed or hardwired.
•     A microprogram is a program written in a low-level language that is implemented by the hardware.
•     Hardwired control units consist of hardware that directly executes machine instructions.
•     Detailed organization of a processor implementation

                  1.  How the control unit interprets machine instructions (from fetch thru execute stages)

•     There can be different implementations of a single ISA
•     In the book this level is called “Control level”

                                                     Level 0: Digital Logic Level

•     This level is where we find digital circuits (the chips).
•     Digital circuits consist of gates and wires.
•     These components implement the mathematical logic of all other levels.
•     This level is where we view physical devices as just switches (On/Off)
•     Instead of viewing their physical behavior (i.e. in terms of voltages and currents) we use two value logic i.e. 0 (off) and 1(on)
•     We will briefly look at the physical electronic components – mainly the transistor technology 

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