【正文】 lberschatz, Galvin, and Gagne ?1999 Applied Operating System Concepts Dynamic Loading ? Routine is not loaded until it is called.（ 例程在調(diào)用之前并不執(zhí)行） ? Better memoryspace utilization。） ? Stub replaces itself with the address of the routine, and executes the routine.（ 存根用例程地址來(lái)替換自己，以及執(zhí)行例程。 also referred to as virtual address.（ 邏輯地址 —由 CPU產(chǎn)生；也叫做虛擬空間。） ? The user program deals with logical addresses。 must provide direct access to these memory images.（ 備份區(qū) —是一個(gè)固定的足夠大的可以容納所有用戶內(nèi)存映像的拷貝；對(duì)于可以讓這些內(nèi)存映像直接存取。 total transfer time is directly proportional to the amount of memory swapped.（ 交換時(shí)間的主要部分是轉(zhuǎn)移時(shí)間，總的轉(zhuǎn)移時(shí)間直接同交換的內(nèi)存的數(shù)量成比例。） ? Singlepartition allocation（ 單獨(dú)分區(qū)分配） – Relocationregister scheme used to protect user processes from each other, and from changing operatingsystem code and data.（基址寄存器策略由來(lái)保護(hù)用戶進(jìn)程（同其他進(jìn)程和改變的操作系統(tǒng)代碼和數(shù)據(jù)分開(kāi)。 holes of various size are scattered throughout memory.（ 分區(qū) —可用的內(nèi)存塊，不同大小的分區(qū)分布在整個(gè)內(nèi)存中。 must search entire list, unless ordered by size. Produces the smallest leftover hole. （ 搜索整個(gè)序列，找到適合條件的最小的分區(qū)進(jìn)行分配。） Firstfit and bestfit better than worstfit in terms of speed and storage utilization.（ 在速度和存儲(chǔ)的利用上，首先適應(yīng)和最佳適應(yīng)要比最差適應(yīng)好。） – Compaction is possible only if relocation is dynamic, and is done at execution time.（ 只有重置是動(dòng)態(tài)的時(shí)候，才有可能進(jìn)行壓縮，壓縮在執(zhí)行時(shí)期進(jìn)行） – I/O problem（ I/O問(wèn)題） ? Latch job in memory while it is involved in I/O.（ 當(dāng) I/O的時(shí)候，把工作鎖定在內(nèi)存中。） ? Divide physical memory into fixedsized blocks called frames (size is power of 2, between 512 bytes and 8192 bytes).（ 把物理內(nèi)存分成大小固定的塊。） ? Set up a page table to translate logical to physical addresses. （ 建立一個(gè)頁(yè)表，把邏輯地址轉(zhuǎn)換為物理地址。） Silberschatz, Galvin, and Gagne ?1999 Applied Operating System Concepts Address Translation Architecture Silberschatz, Galvin, and Gagne ?1999 Applied Operating System Concepts Paging Example Silberschatz, Galvin, and Gagne ?1999 Applied Operating System Concepts Implementation of Page Table ? Page table is kept in main memory.（ 主存中的頁(yè)表） ? Pagetable base register (PTBR) points to the page table.（ 頁(yè)表基址寄存器指向頁(yè)表） ? Pagetable length register (PRLR) indicates size of the page table.（ 頁(yè)表限長(zhǎng)寄存器表明頁(yè)表的長(zhǎng)度） ? In this scheme every data/instruction access requires two memory accesses. One for the page table and one for the data/instruction.（ 在這個(gè)機(jī)制中，每一次的數(shù)據(jù) /指令存取需要兩次內(nèi)存存取，一次是存取頁(yè)表，一次是存取數(shù)據(jù)） ? The two memory access problem can be solved by the use of a special fastlookup hardware cache called associative registers or translation lookaside buffers (TLBs). (通過(guò)一個(gè)聯(lián)想寄存器，可以解決兩次存取的問(wèn)題） Silberschatz, Galvin, and Gagne ?1999 Applied Operating System Concepts Associative Register ? Associative registers – parallel search （ 聯(lián)想寄存器 —并行查找） Address translation (A180。 is in associative register, get frame out. （ 如果 A’在聯(lián)想寄存器中，把頁(yè)框 取出來(lái)。） ? Hit ratio = ? ? Effective Access Time (EAT)（ 有效存取時(shí)間） EAT = (1 + ?) ? + (2 + ?)(1 – ?) = 2 + ? – ? Silberschatz, Galvin, and Gagne ?1999 Applied Operating System Concepts Memory Protection ? Memory protection implemented by associating protection bit with each frame.（ 內(nèi)存的保護(hù)由與每個(gè)頁(yè)框相連的保護(hù)位來(lái)執(zhí)行。） – a page offset consisting of 12 bits.（ 一個(gè) 12位的偏移。） ? Even though time needed for one memory access is quintupled, caching permits performance to remain reasonable.（ 盡管每次內(nèi)存存取的時(shí)間是很大的，高速緩存使執(zhí)行的時(shí)間還是可以接受的。） ? Decreases memory needed to store each page table, but increases time needed to search the table when a page reference occurs.（ 減少內(nèi)存需要儲(chǔ)存每個(gè)頁(yè)表，但是當(dāng)訪問(wèn)一個(gè)頁(yè)時(shí)，尋找頁(yè)表需要增加時(shí)間。） ? Private code and data （ 私有代碼和數(shù)據(jù)） – Each process keeps a separate copy of the code and data.（ 每個(gè)進(jìn)程保留一個(gè)代碼和數(shù)據(jù)的私有拷貝。 each table entry has（ 段表 映射二維物理地址，每個(gè)表項(xiàng)包括） : – base– contains the starting physical address where the segments reside in memory.（ 基址 包括內(nèi)存中段物理地址的起始地址。（ 段表限長(zhǎng)寄存器表明被一個(gè)程序所使用的段的數(shù)目。） ? A segmentation example is shown in the following diagram（下面的是一個(gè)段的例子） Silberschatz, Galvin, and Gagne ?1999 Applied Operating System Concepts Silberschatz, Galvin, and Gagne ?1999 Applied Operating System Concepts Segmentation with Paging – MULTICS ? The MULTICS system solved problems of external fragmentation and lengthy search times by paging the segments.（ MULTICS系統(tǒng)通過(guò)結(jié)合分頁(yè)解決外碎片問(wèn)題和搜索時(shí)間長(zhǎng)的