Demand paging scheme

• Job is compiled from addresszero onwards.
• Job is divided into pages.
• The memory is divided into blocks. Paging hardware is required.

Pages are loaded into the main memory without correcting addresses.

At least one page of the job lies in the memory. Other pages are brought into the main

memory as earlier paging scheme.

Advantages of demand principle:           

1. User written error routines are rarely required. Use demand principle, i.e, load an error routine only if it is required.
2. Input and output routines are not required throughout the execution of a program load them as required.
3. Some portions of a program are mutually exclusive.
4. Look up tables let us say, we make a table for sinelet X = 4152 34.896"

let us say , 1 page is for 1, than for 0-90 we need 90k.

so, we require too much memory (90k). so , demand  paging scheme can be used to

save memory.

• Don’t load the table during execution
• load just one page determined by the demand

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