Question

Is there a relation between overlays and contiguous allocation?

Comments

nice! you modified the tesbook question!!!

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yes I didnt feel the need for the whole question as this is the only part that confused me

can you explain the relation

Answer 1

Overlays are a solution to the limitation of contiguous memory allocation. Overlay is a memory management technique used by the programmers to split their object code into independent sections which are dynamically loaded whenever required by the overlay driver. Overlay area is the contiguous memory allocated to the user programs. But only the required instructions need to be loaded in memory at a time not the entire program. Common data and routines may be kept in memory. Needed instructions and data replace those no longer in use. It overcomes the problem of limited size of programs that can be loaded into main memory. Virtual Memory accomplishes similar goals.

Comments

but virtual memory can use non contiguous right?

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Your comment is not exactly right. Virtual memory is abstraction of contiguous memory which is physically not contiguous in memory, may be in different pages in memory. Also overlays has some overhead on the programmer. In case of virtual memory, programmer need not to bother.

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ok so is this right to say that overlay will always be contiguous both as an abstraction and physically but virtual memory may or may not be contiguous physically?

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Overlays are not generally used with virtual memory management technique. Yes it is physically contiguous and virtual memory may or may not be physically contiguous.