OS Walkthrough 04— File Management & I/O

PKU’s OS on Coursera: Week 09 ~ Week 11

The notes I took here were fewer since I was not quite fascinated by the contents over these 3 weeks.

This article is about FCB (file control block), abstraction, HDD vs. SSD, file system data structure, block cache, disk scheduling algorithm of HDD [FCFS (first come first serve), SSTF (shortest seek time first), SCAN, C-SCAN] , RAID, & I/O management diagram.

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OS Walkthrough 03 — Memory Management

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OS Walkthrough 05 — Deadlock

(1) Week 09: File Management-1

(2) Week 10: File Management-2

(1) Week 09: File Management-1

1. File name — (mapping) — > disk space
2. FCB (file control block): A file has its unique FCB, and a file directory entry is an FCB.

• cf. PCB (process control block)

3. Abstraction

• Files are abstractions of disks
• Address spaces are abstractions of memory
• Processes are abstractions of CPU

4. HDD vs. SSD / sector / disk head

5. File system data structure

• Bitmap
• Idle block list
• Idle block linked list

6. Cache writing policies

• Write-through: More costly but safer.
• Write-back (or write-behind): Lazy-write. More efficient but less safe than write-through.
• Transaction log

7. Read-ahead: Read more for data blocks, read less for code blocks

8. Direct memory access (DMA)

(2) Week 10: File Management-2

1. Windows — FAT16 & FAT32
2. Block cache
3. HDD:

• Seek time
• Rotational latency

1. Disk scheduling algorithm of HDD

• FCFS (First Come First Serve)
• SSTF (Shortest Seek Time First)
• SCAN
• C-SCAN / N-step-SCAN / FSCAN

4. RAID: “redundant array of independent disks” or “redundant array of inexpensive disks”

• RAID 0: a stripe set or striped volume.
• RAID 1: consists of an exact copy (or mirror) of a set of data on two or more disks
• RAID 4: consists of block-level striping with a dedicated parity disk.

(3) Week 11: I/O

I/O management diagram & a typical PC bus structure [1] [2]

(4) References

[1] https://www.cs.uic.edu/~jbell/CourseNotes/OperatingSystems/13_IOSystems.html

[2] https://www.tutorialspoint.com/operating_system/os_io_software.htm