Storage
There are three types of storage:
- volatile storage
- nonvolatile storage
- stable storage
In stable storage, several copies of information are stored on various disk blocks.
Data Access :
The transactions input information from the disk to the main memory and then output the information back onto the disk.
Physical Block: The blocks residing on the disk are known as ‘Physical Block’.
Buffer Block: The blocks residing temporarily in the main memory
are known as ‘Buffer Block’.
Disk Buffer: The area of memory where a block resides temporarily is called the ‘Disk Buffer’.
Block Transfer:
a) Input (B): Transfers the physical block B to main memory.
b) Output (B): Transfers the buffer block B to the disk and replaces the appropriate physical block there.
c) Read (X): Assigns the value of data item (X) to the local variable x. It executes the following operations :
i) If block Bx on which X resides is not in main memory, it issues input(Bx).
ii) It assigns to x the value of X from the buffer block.
d) write (X): Assigns the value of local variable x to data item X in the buffer block. It executes the following operations :
i) If block Bx on which X resides is not in main memory, it issues input(Bx).
ii) It assigns the value of x to X in buffer Bx.
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