Background Virtual Memory(虚拟存储器) 是指具有请求调页功能和置换功能，能从逻辑上对内存容量 加以扩充的一种存储器系统 Logical size: 从系统角度看：内存容量+外存容量 从进程角度看：地址总线宽度范围内；内存容量+外存容量 Speed:close to main memory Cost per bit:close to secondary storage(disks) Virtual memory separation of user logical memory from physical memory. Only part of the program needs to be in memory for execution Logical address space can therefore be much larger than physical address space Allows address spaces to be shared by several processes Allows for more efficient process creation 4口”484在4色，主月QC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Background ▶ Virtual Memory (虚拟存储器) 是指具有请求调页功能和置换功能，能从逻辑上对内存容量 加以扩充的一种存储器系统 ▶ Logical size: 从系统角度看：内存容量＋外存容量 从进程角度看：地址总线宽度范围内；内存容量＋外存容量 ▶ Speed: close to main memory ▶ Cost per bit: close to secondary storage (disks) ▶ Virtual memory : separation of user logical memory from physical memory. ▶ Only part of the program needs to be in memory for execution ▶ Logical address space can therefore be much larger than physical address space ▶ Allows address spaces to be shared by several processes ▶ Allows for more efficient process creation