Q

"Roll" memory and "page" memory explained

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Could you tell me the difference between "roll" memory and "page" memory? I'm using an Oracle/Unix-based OLTP System. I am not a techie.

I'm not quite sure what "roll" is as it refers to Operating Systems. But I can give you an idea of paging and swapping.

Computers have a finite amount of memory. It would be great if all of your programs could fit into that memory. But this is often not the case. To make computers appear as if they have more physical memory (RAM) than they do, we can temporarily use some space on disk. Any space used on disk for the computer's memory is called Virtual Memory.

When a program executes, its instructions are placed into memory. A unit of memory than can hold a programs instructions is called a "page". If the physical memory, or RAM, becomes full, the OS can take portions, or pages of memory that are not currently being used and copy them to disk, copy them to the Virtual Memory. So a page of memory is written to disk. When the instructions in that page are needed, the system reads that page of memory from disk. This often requires a page of memory to be written to disk first to make room for the page to be read in.

If an entire program is moved from memory to disk, this is called a "swap". Swapping can kill performance of any server. If only a portion of a program is moved to disk, this is called "paging".

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This was first published in August 2002

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