Background Virtual memory can be implemented via: 1.Demand paging Paging technology pager(请求调页)and page replacement Pager VS.swapper the unit of swapping in/out is not the entire process but page. 2.Demand segmentation 4口”4814在，4色，主)QC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Background ▶ Virtual memory can be implemented via: 1. Demand paging ▶ Paging technology + pager (请求调页) and page replacement ▶ Pager VS. swapper the unit of swapping in/out is not the entire process but page. 2. Demand segmentation
虚拟存储器的特征 1.多次性：最重要的特征 ·一个作业被分成多次装入内存运行 2.对换性 一允许在进程运行的过程中，（部分）换入换出 3.虚拟性 ·逻辑上的扩充 ·虚拟性是以多次性和对换性为基础的。 。多次性和对换性是建立在离散分配的基础上的 4口”484在4色，主月QC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 虚拟存储器的特征 1. 多次性：最重要的特征 ▶ 一个作业被分成多次装入内存运行 2. 对换性 ▶ 允许在进程运行的过程中，（部分）换入换出 3. 虚拟性 ▶ 逻辑上的扩充 ▶ 虚拟性是以多次性和对换性为基础的。 ▶ 多次性和对换性是建立在离散分配的基础上的
Virtual-address Space(虚拟地址空间) The virtual address space of a process refers to the logical (or virtual)view of Max how a process is stored in memory. stack Typically:0~xxx exists in contiguous memory In fact,the physical memory are organized (partitioned)in page frames the page frames assigned to a process may not be heap contiguous→MMU data code 4口”484在4色，主月QC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Virtual-address Space (虚拟地址空间) ▶ The virtual address space of a process refers to the logical (or virtual) view of how a process is stored in memory. ▶ Typically: 0~xxx & exists in contiguous memory ▶ In fact, the physical memory are organized (partitioned) in page frames & the page frames assigned to a process may not be contiguous⇒MMU Max 0 stack ❄ ✻ heap data code
Some benefits 1.Shared library using virtual memory stack stack shared library shared pages shared library heap heap data data code code 2.Shared memory 3.Speeding up process creation 4口”4814在4色，主QC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Some benefits 1. Shared library using virtual memory stack stack heap heap data data code code shared library shared pages shared library 2. Shared memory 3. Speeding up process creation
Outline Demand Paging(按需调页 Basic Concepts(Hardware support) Performance of Demand Paging 4口”4814在，4色，主)QC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Outline Demand Paging (按需调页) Basic Concepts (Hardware support) Performance of Demand Paging