A virtual machine is a program running on a computer that creates a self-contained operating environment and presents the appearance to the user of a different computer. A virtual machine simulates at a minimum the instruction set of the computer it emulates.
A virtual memory is a technique for creating the illusion that a computer has more memory than it really has by swapping blocks or pages of data between memory and external storage.
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Virtual memory: Memeory that’s not really there. Computer’s Operating system takes a portion of the hard disk and fakes it like memory to keep the applications happy.
Virtual machine: Machine that’s not really there. A software — like a java program — interacts with this shell (not really the computer itself). That program has to know only how to interact with the virtual machine — It doesn’t need to know anything about the underlying hardware.
Virtual Machine:A software program that emulates a hardware system.In general terms, a virtual machine in computer science is software that creates an environment between the computer platform and the end user in which the end user can operate software.
Common, meaning of virtual machine is a piece of computer software that isolates the application being used by the user from the computer. Because versions of the virtual machine are written for various computer platforms, any application written for the virtual machine can be operated on any of the platforms, instead of having to produce separate versions of the application for each computer and operating system. The application is run on the computer using an interpreter or Just In Time compilation.The Term Virtual Machine coined most commonly in Java programming language.
Virtual Memory:Memory, often as simulated on a hard disk, that emulates RAM, allowing an application to operate as though the computer has more memory than it actually does.This memory created by using the hard disk to simulate additional random-access memory; the addressable storage space available to the user of a computer system in which virtual addresses are mapped into real addresses.
Most frequently Virtual memory is combination of RAM of your system and swapped memory from your Hard Disk Drive. This memory regulated by size of paging files.
Diference between Virtual machine and virtual memory is:
In virtual machine software emulates the operating system environment.
In virtual memory hardware simulates (CPU+RAM+MMU(Memory Management Units)) virtual memory of system based on size of paging file.
VIRTUAL MACHINE is software that creates an environment between the computer platform and the end user in which the end user can operate software.
The original meaning of virtual machine is that of a number of different identical execution environments on a single computer, each of which exactly emulates the host computer. This provides each user with the illusion of having an entire computer, but one that is their “private” machine, isolated from other users, all on a single physical machine.
VIRTUAL MEMORY is the use of space on a hard disk drive (HDD) to simulate additional main memory.
Memory is used to hold portions of the operating system, programs and data that are currently in use or that are frequently used. Physically, main memory (also referred to as primary memory) consists of random access memory (RAM) chips that are combined into modules which, in turn, are inserted into slots on the motherboard (i.e., the main circuit board) on a computer. The times required to access different addresses (i.e., locations) in RAM are extremely short and nearly equal, in contrast to the varying delay times for accessing locations on the HDD and other storage devices.
In order to free up space in memory, an operating system with a virtual memory capability transfers data that is not immediately needed from memory to the HDD; when that data is needed again, it is copied back into memory. That is, when all of the RAM is being used (e.g., if there are many programs open simultaneously or if one very large program is in use), a computer with virtual memory enabled will swap data to the HDD and back to memory as needed, thus, in effect, increasing the total system memory.
Virtual memory permits software to run in a memory space (i.e., a logical memory) whose size is greater than the computer’s RAM. Most personal computers sold today contain from 256MB to 1024MB of RAM. While this is huge in comparison to what was common just a few years ago, it is still often insufficient to simultaneously run all of the programs that users attempt to run. The reason is that the size of many programs has continued to increase accompanying the growth in memory sizes and HDD capacities, largely in order to add more features (including fancier graphics).
Application programs cannot distinguish between primary memory and virtual memory, and thus they run as if all the data is in primary memory. Virtual memory is likewise usually invisible to the user. However, its existence can become apparent in the form of degraded performance if it is used too heavily, because the CPU (central processing unit) will spend more of its time copying data back and forth to the HDD and less of its time doing useful work. This is termed thrashing. The reduced efficiency is also a result of the facts that HDDs are far slower than RAM and that they are not designed for accessing small pieces of data (e.g., single bytes) one at a time.
and they r 2 diffrent concepts and cant b compared…
Hey u messed them completely!
actually they r world apart.
Virtual machine is a collection of software that provides run time environment(eg data structure support) to ur applications like v have JVM(java vitual m/c).Only the JVM knows abt the internal architecture of ur computer,the applications thus become portable.For appl.s VM is the architecture support and for VM the actual architecture is with which it is communicating.The memory used is still that of the original h/w.
Virtual memory : This is system memory that is simulated by the hard drive. When all the RAM is being used (for example if there are many programs open at the same time) the computer will swap data to the hard drive and back to give the impression that there is slightly more memory
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