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THE INSTRUCTION SET ARCHITECTURE using barcode integration for vs .net control to generate, create pdf 417 image in vs .net applications. Recommended GS1 barcodes for mobile apps The Instruction Set The i visual .net pdf417 nstruction set is the collection of instructions that a processor can execute, and in effect, it de nes the processor. The instruction sets for each processor type are completely different one from the other.

They differ in the sizes of instructions, the kind of operations they allow, the type of operands they operate on, and the types of results they provide.This incompatibility in instruction sets is in stark contrast to the compatibility of higher level languages such as C, Pascal, and Ada. Programs written in these higher level languages can run almost unchanged on many different processors if they are re-compiled for the target processor.

(One exception to this incompatibility of machine languages is programs compiled into Java bytecodes, which are a machine language for a virtual machine. They will run unchanged on any processor that is running the Java Virtual Machine. The Java Virtual Machine, written in the assembly language of the target machine, intercepts each Java byte code and executes it as if it were running on a Java hardware ( real ) machine.

See the Case Study at the end of the chapter for more details.) Because of this incompatibility among instruction sets, computer systems are often identi ed by the type of CPU that is incorporated into the computer system. The instruction set determines the programs the system can execute and has a signi cant impact on performance.

Programs compiled for an IBM PC (or compatible) system use the instruction set of an 80x86 CPU, where the x is replaced with a digit that corresponds to the version, such as 80586, more commonly referred to as a Pentium processor. These programs will not run on an Apple Macintosh or an IBM RS6000 computer, since the Macintosh and IBM machines execute the instruction set of the Motorola PowerPC CPU. This does not mean that all computer systems that use the same CPU can execute the same programs, however.

A PowerPC program written for the IBM RS6000 will not execute on the Macintosh without extensive modi cations, however, because of differences in operating systems and I/O conventions. We will cover one instruction set in detail later in the chapter. Software for generating machine language programs A compiler is a computer program that transforms programs written in a high-level language such as C, Pascal, or Fortran into machine language.

Com-. THE INSTRUCTION SET ARCHITECTURE pilers for the same high pdf417 for .NET level language generally have the same front end, the part that recognizes statements in the high-level language. They will have different back ends, however, one for each target processor.

The compiler s back end is responsible for generating machine code for a speci c target processor. On the other hand, the same program, compiled by different C compilers for the same machine can produce different compiled programs for the same source code, as we will see. In the process of compiling a program (referred to as the translation process), a high-level source program is transformed into assembly language, and the assembly language is then translated into machine code for the target machine by an assembler.

These translations take place at compile time and assembly time, respectively. The resulting object program can be linked with other object programs, at link time. The linked program, usually stored on a disk, is loaded into main memory, at load time, and executed by the CPU, at run time.

Although most code is written in high level languages, programmers may use assembly language for programs or fragments of programs that are time or space-critical. In addition, compilers may not be available for some special purpose processors, or their compilers may be inadequate to express the special operations which are required. In these cases also, the programmer may need to resort to programming in assembly language.

High level languages allow us to ignore the target computer architecture during coding. At the machine language level, however, the underlying architecture is the primary consideration. A program written in a high level language like C, Pascal, or Fortran may look the same and execute correctly after compilation on several different computer systems.

The object code that the compiler produces for each machine, however, will be very different for each computer system, even if the systems use the same instruction set, such as programs compiled for the PowerPC but running on a Macintosh vs. running on an IBM RS6000. Having discussed the system bus, main memory, and the CPU, we now examine details of a model instruction set, the ARC.

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