Ch. 9 Secondary Storage Flashcards
What are the 5 common Disk Scheduling Strategies?
> First Come First Serve (FCFS/FIFO)
Shortest Seek Time First (SSTF)
SCAN (“Elevator”)
C-SCAN (circular SCAN)
C-LOOK (circular LOOK)
Attributes of Memory
> Volatile (lose data on shutdown)
Transient (impermanent)
Controlled by OS
Attributes of Secondary Storage
> Non-volatile (data kept when machine is off)
Persistent (permanent until deleted)
Can be controlled by users
What is the most costly component of a disk I/O operation?
A. Seek Time
B. Rotational Time
C. Transfer Time
A) Seek Time.
Requires motor movement of the read/write head (slow)
Seek Time
Cost of moving the read/write head to the right position (motor movement)
Rotational Time
Time to wait until the disk rotates into position
Transfer Time
Time taken to read/write the data
Disk scheduling strategies try to reduce which component of a disk I/O operation
Seek Time.
Scheduling strategies schedule multiple disk requests
If a process is forked, will the parent and child process share the same files?
Yes, even though they run independently, the parent and child share the same files. The read/write pointer for the file is the same for the parent and child.
What does a directory contain?
A directory is just a file with a list of file names and a pointer (index for entry in I-Node table)
Contiguous Allocation
Allocate disk space like paged segmented memory. Keep a free list of unused disk space.
Chained Allocation
Indexed Allocation
Allocate an array of pointers during the file creation. Fill the array as new disk blocks are assigned.
Name 3 ways file systems maintain a list of free blocks
> Bit Vectors
Linked list
Indexing
Why is it desirable to use segmentation?
A segment is smaller than a whole process which means less I/O time is required to swap a segment.
