OS的四大子系统
| Process | Memory | I/O Devices | File |
|---|---|---|---|
| Hardware | Hardware | Hardware | Software |
逻辑组织
- 文件管理
- 系统文件的逻辑组织
- 文件目录
- 文件共享
- 文件存储空间的管理
文件管理（File Management）
- File management system is consideredpart of the operating system.文件管理系统被认为是操作系统的一部分。
- Input to applications is by means of a file.应用程序的输入是通过文件进行的。
- Output is saved in a file for long-termstorage. 输出保存在文件中以便长期存储。
Objectives for a File Management System
- Meet the data management needs and
requirements of the user.
(符合系统管理数据的需要及用户的需求) - Guarantee that the data in the file are valid.
(确保文件中的数据有效) - Optimize performance.
(保证系统性能及用户对响应时间的要求) - Provide I/O support for a variety of storagedevice types.
(为各种存储设备类型提供I/O支持) - Minimize or eliminate the potential forlost or destroyed data.
(减少或避免数据丢失及损坏) - Provide a standardized set of L/Ointerface routines.
(提供标准的IO接口) - Provide I/O support for multiple users.
(支持多用户环境下多个用户的IO操作)
File Management Functions
- Identify and locate a selected file.
标识并找到选定的文件。 - Use a directory to describe the location ofall files plus their attributes.
使用目录来描述所有文件的位置以及它们的属性。 - On a shared system describe user accesscontrol.
在共享系统上描述用户访问控制。 - Blocking for access to files.
阻止对文件的访问。
-Allocate files to free blocks.
将文件分配给空闲块。 - Manage free storage for available blocks.
-管理可用区块的空闲空间。
Device Drivers
- Lowest level.
最低级别。 - Communicates directly with peripheraldevices.
直接与外围设备通信。 - Responsible for starting I/O operationson a device.
负责启动I/O操作设备。 - Processes the completion of an I/orequest.
处理I/O请求的完成。
Basic File System
- Physical I/O.
物理I/O - Deals with exchanging blocks of data.
处理数据块的交换。 - Concerned with the placement of blocks.
与块的放置有关 - Concerned with buffering blocks in main memory.
与内存中的缓冲块有关。
Basic I/O Supervisor
- Responsible for file I/O initiation andtermination.
- Control structures are maintained.
- Concerned with scheduling access tooptimize performance.
- I/O buffers are assigned and secondarymemory is allocated.
Logical I/O
-
Enables users and applications to access records.
允许用户和应用程序访问记录。 -
Provides general-purpose record I/ocapability.
提供通用记录I/ocapability。 -
Maintains basic data about file.
维护有关文件的基本数据。
Access Method
- Reflect different file structures.
- Different ways to store and process data.
如Pile、顺序访问、索引顺序访问、索引访问、Hash访问法等访问方法
File Organization
- File organization refers to the logicalstructuring of the records as determinedby the way in which they are accessed.
文件组织是指由访问方式决定的记录的逻辑结构。 - The physical organization of the file onsecondary storage depends on theblocking strategy and the file allocationstrategy.
存储上文件的物理组织取决于阻塞策略和文件分配策略。
Criteria for File Organization
- Rapid access
Needled when accessing a single record.
Not needed for batch mode. - Ease of update
File on CD-ROM will not be updated, so thisis not a concern. - Economy of storage
Should be minimum redundancy in the data.- Redundancy can be used to speed accesssuch as an index.
-Simple maintenance· - Reliability
File Organization
- Pile file（堆文件)
- Sequential file（顺序文件)
- Indexed sequential file（索引顺序文件)
- Indexed file（索引文件)
- Direct, or Hashed file（直接或hash文件)
堆文件（pile）
- Data are collected in the order theyarrive.
数据是按到达的顺序收集的。 - Purpose is to accumulate a mass of data and save it.
目的是积累大量数据并保存它。 - Records may have different fields.
记录可能有不同的字段。 - No structure.
无结构文件。
顺序文件（Sequential File）
- Fixed format used for records.
用于记录的固定格式。 - Records are the same length.
记录的长度相同。 - All fields the same (order and length).
所有字段都相同(顺序和长度)。 - Field names and lengths are attributes ofthe file.
字段名和长度是文件的属性。
One field is the key filed
-Uniquely identifies the record.
-Records are stored in key sequence. - The only one that is easily stored on tapes as wellas disk .
唯一 一种可以同时存储在磁带和磁盘上的。 - Typically used in batch applications and theapplications processing of all records.
通常用于批处理应用程序和处理所有记录的应用程序。 - For querying and/or updating an individlual record，it provides poor performance.
对于查询和/或更新单个记录，它的性能较差。 - New records are placed in a log file or transactionfile.
新记录放置在日志文件或transactionfile中。 - Batch update is performed to merge the log filewith the master file.
执行批更新以将日志文件与主文件合并。
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