七章节存储器管理课件

1、第七讲 存储器管理中国科学技术大学计算机系 陈香兰2013Fall内容提要存储器的层次结构程序执行的基础知识、程序的装入和链接连续分配存储管理方式分页存储管理方式分段存储管理段页式存储管理存储器的层次结构存储器是计算机系统的重要组成部分容量、价格和速度之间的矛盾内存、外存；易失性和永久性内存，是稀缺资源在现代计算机系统中，存储通常采用层次结构来组织多级存储器结构主存与寄存器高速缓存和磁盘缓存多级存储器结构Storage systems in a computer system can be organized in a hierarchySpeed, access timeCost per b

2、itVolatility高级缓冲技术cachingCachingCopying information into faster storage systemWhen accessing, first check in the cache, ifIn: use it directlyNot in: get from upper storage system, and leave a copy in the cacheUsing of cachingRegisters provide a high-speed cache for main memoryInstruction cache & dat

3、a cacheMain memory can be viewed as a fast cache for secondary storageMagnetic disks 磁盘Transfer time 传输时间TT data size * Transfer rateTransfer rate (n M/s)-1 ( n Byte/us )-1 1/n us/BytePositioning time 定位时间Seek time 寻道TsRotational latency 旋转延迟TRTP Ts +TR m msTT VS. TPPlease Store data closely 程序执行的基础

4、知识Von Neumann architecture 冯诺依曼体系结构（图）Program must be brought into memoryMain memory is usually too smallProcessProgram must be placed within a process for it to be executed作业池User programsWhere to place the programseveral steps（图）地址的类型Absolute address 绝对地址Address seen by the memory unitPhysical add

5、ress 物理地址Relative address 相对地址Linear address 线性地址Logical address 逻辑地址Generated by the CPUVirtual address 虚拟地址When can the absolute address can be decided?Address binding 地址的绑定Address binding 地址绑定, the binding of instructions and data to memory, 可以在三种时刻进行Compile timeIf memory location known a priori,

6、 absolute code can be generated; must recompile code if starting location changes.Load timeMust generate relocatable code if memory location is not known at compile time.Execution timeBinding delayed until run time if the process can be moved during its execution from one memory segment to another.

7、Need hardware support for address maps (e.g., base and limit registers)Memory-Management Unit (MMU)Hardware device, 逻辑地址 物理地址Relocation register 重定位寄存器Added to every address generated by a user process at the time it is sent to memoryE.g. MS-DOS on 80 x86User program deals with logical addresses, it

8、 NEVER sees the real physical addresses.是否需要将进程的所有代码和数据一次性装入？Shall we put the entire program & data of a process in physical memory before the process can be executed?For better memory space utilizationDynamic loadingDynamic linkingOverlaysSwapping绝对装入方式编译时，产生absolute code，即使用绝对地址的代码装入时，必须装入到指定的地址无需

9、对程序和数据的地址进行修改适用于单道系统可重定位装入方式大多数情况下，不能预知装入地址，只能在装入时确定编译时，产生可重定位代码，即使用相对地址的代码装入时，必须重定位通常把在装入时对目标程序中指令和数据的修改过程称为重定位。由于地址变换是在装入时一次性完成的，以后不再改变，故称为静态重定位可用于多道系统动态运行时重定位有时候，程序会在内存中移动位置例如对换需要能支持在运行过程中动态改变程序在内存中的位置方法：推迟重定位时机即从相对地址到绝对地址的转换推迟到程序真正执行时才进行因此，装入内存中的代码和数据的地址仍然是相对地址需要重定位寄存器的支持动态运行时装入方式根据程序运行的局部性，让程序及

10、其数据在需要时才被装入Better memory-space utilization; unused routine is never loaded.Useful when large amounts of code are needed to handle infrequently occurring casesError routine No special support from OS is required implemented through program designDue to the users Overlays 覆盖技术Keep in memory only those are needed at any given time.Needed when process is larger than amount of memory allocated to it.Implemented by user, no special support needed from OS, programming design of overlay structure is complex程序的链接多个源程序编译多个目标模块；库。需要链接成可装入模块根据链接时间的不同静态链接方式：装入前很早就链接装入时动态链接：边装入，边链接运行时动态链接：运行时才链接