abstraction：抽象

As this figure suggests, files are abstractions for I/O devices, virtual memory is an abstraction for both the main memory and disk I/O devices, and processes are abstractions for the processor, main memory, and I/O devices.

如图所示，文件是I/O设备的抽象，虚拟内存是内存和磁盘I/O设备的抽象，处理过程是处理器、内存和I/O设备的抽象。