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Scheduling

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Hi

1) What is the diference between Pages (pagefile pages) and frames?

2) What is the difference between Paged and Segmented Viertual Memory ?

3)Normally a big application when executed more times, its execution time is completed in much less than the first run. But why it is not same case with small application, they often have a little longer run time than first run, why?

Thanks

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The Memory Manager of your PCs Operating System uses pages are 4KB in size as the basic unit for memory allocation. This applies also when the memory contents are “Paged to Disk” (Put in virtual memory.)
Frames are the information in a transmitted data packet (Think Internet) telling the router where the Packet is to go, where it is from, how big it is, end point, etc.
They surround the data, thus the name.

All virtual memory written on the hard disk is paged.
Segmented addressing of memory was used in DOS.
Segmenting can also refer to the old page frames (Different meaning of frame.) of the LIM standard Expanded Memory used before extended memory existed.
(Think original IBM PC.)
Expanded memory allowed Lotus 123 (main application used at that time.) to address more than 640K memory, (DOS limit) and have 8 meg.

Second “instances” of large programs “run” faster because Windows shares (uses) the .exe and .dll files of the first instance and does not load a second copy of them. (Hard Disks are slow)
Only the data is a new file.

Small applications run slower with multiple instances because of the large “overhead” in “task switching” Windows. (The Operating System spends more time storing the register contents, reloading the next register contents, checking “security”, etc. than it does in running the programs.)
Task Switching consumes a lot of clock cycles.

I hope I have not used too much new vocabulary in this explanation. These are fundamental questions of computer software design, so it is necessary.

Regards, Chris

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