The content is based on the notes made during the class review, and the illustrations are mostly from the screenshots of the course
File Storage Management
In fact, the main topic is how to manage the free area and the corresponding usage issues. Right now
- allocated when in use
- recycle after use
| method | Be applicable | characteristic |
|---|---|---|
| free list method | continuous | There are different allocation algorithms, and multimedia files may also use this method |
| Free Disk Chain | Discrete | The operating system keeps chain head and chain tail pointers |
| chain of free extents | discrete/continuous | Same as above, and the free block records the length of the extent and the pointer of the next extent, and the retrieval speed can be improved by explicit linking (building a table) |
| bitmap | discrete/continuous | Involving (font size, bit number) to the calculation of the block |
| group chaining | discrete/continuous | Suitable for large file systems |
Free disk block method: allocate the head of the unchained chain, and recover the tail of the chain.
Bit diagram method: the corresponding bit must be changed before allocation and recycling
Group link method: (essentially a link of a fixed-length stack) allocation and recovery must deal with the situation where the stack is empty and the stack is full. When the stack is full, a new stack must be built and a pointer to the previous stack saved. When the stack is empty during allocation, it must be read into the next stack. The last block has an end mark (one less data is stored)
courseware
