物理和虚拟内存之间的差异

Physical vs Virtual Memory

Physical memory and Virtual memory are two forms of memory used for storing data in a computer. Physical memory refers to chips such as RAM (Random Access Memory) memory and storage devices such as hard disks that are used to store data. Virtual memory is a memory space created by Operating system when the computer does not have enough physical memory to execute a program. Virtual memory is created by combining RAM with the hard drive space. Virtual memory allows executing large programs faster when the RAM is not enough.

Physical Memory

As mentioned earlier, physical memory refers to the RAM and the hard disks in the computer that are used to store data. In a computer the operating system, application programs and currently used data are kept in the RAM, so that they could be accessed quickly by the processor. RAM could be accessed faster than the other storage devices such as the hard disk and CD-ROM. But the data in the RAM exists only while the computer is running. When the power is turned off, all the data in the RAM are lost and the operating system and other data are loaded again to the RAM from the hard disk when the computer is turned on. Hard disk is a non-volatile memory (a memory that keeps data even when it is not powered) that is used to store data in a computer. It is made up of circular disks called platters that stores magnetic data. Data is written and read to and from the platters using read/ write heads.

Virtual Memory

虚拟内存is used when the computer lacks the RAM space for executing a program. Virtual memory combines the RAM space with the hard disk space. When the computer does not have enough RAM space to execute a program, the virtual memory transfers data from the RAM to a paging file, which frees up the space in the RAM. A portion of the hard disk is used to store the page file. This transferring process is done so rapidly so that the user does not feel a difference. Virtual memory can hold an entire block of data while the part that is currently executing resides on the RAM. Therefore the virtual memory allows the operating system to run several programs at the same time thus increasing the degree of multiprogramming. While increasing the size of the programs that could be executed, virtual memory provides cost benefits since hard disk memory is less expensive than the RAM.

What is the difference between Physical and Virtual Memory

While physical memory refers to physical devices that stores data in a computer such as the RAM and hard disk drives, virtual memory combines the RAM space with the hard drive space to store data in the RAM, when the RAM space is not enough. Part of the hard disk is used to store the page files that are used by the virtual memory to store the data that are transferred from the RAM. Even though swapping the data between the page files in the hard disk and the RAM (via the virtual memory) is very fast, too much swapping could slower the overall performance of the system.