VIRTUAL MACHINE

• A virtual machine takes the layered approach to its logicalconclusion. It treats hardware and the operating system kerneas though they were all hardware.
• A virtual machine provides an interface identical to theunderlying bare hardware.
• The operating system creates the illusion of multipleprocesses, each executing on its own processor with its own(virtual) memory.
• The resources of the physical computer are shared to createthe virtual machines.

– CPU scheduling can create the appearance that usershave their own processor.
– Spooling and a file system can provide virtual card readeand virtual line printers.
– A normal user time-sharing terminal serves as the virtualmachine operator’s console.



IMPLEMENTATION OF VIRTUAL MACHINE



-Interpretation of Java bytecode results in slow execution of program.First version of Java Virtual Machine(JVM) implementation was relied on interpretation techniques. On the other hand performance can be improved by translating the Java bytecode into machine code by a Just-In-Time(JIT) compiler and this technique is being integrated into most JVM implementations. Java is an automatic garbage collected language, freeing the programmer from the explicit memory management. Garbage collection "pause" time can be reduced by using a generational garbage collection. This thesis describes an implementation of a JVM. The specific contributions made in this thesis include: development of a Just-In-Time(JIT) compiler using DAG construction technique, a bytecode interpreter, a generational garbage collector. Our implementation can execute Java bytecode either by an interpreter or the bytecode can be translated into machine code using the JIT compiler and the translated code is directly executed by the processor. We have implemented the Java Native Interface (JNI) to enable using C and assembly language programs with Java.





BENEFITS OF VIRTUAL MACHINE



-Virtual machines have been around for a long time but they really have not become common place in many development shops. It is unfortunate since virtual machines provide so many benefits to developers and testers alike. This article will discuss some of the benefits of virtual machines and review two of the most popular virtual machine software packages available for Windows.



EXAMPLE OF VIRTUAL MACHINE



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