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What does Virtual Bytes mean in Worker Processes pane in IIS7.5 Manager?

If I open IIS Manager (On WindowsServer 2008r2), and go to the Worker Processes page, I can see that one of my AppPool processes reports

Private Bytes (KB) 106,435.00
Virtual Bytes (KB) 748,788.00

However, if I look at task manager, the associated w3wp.exe process reports 69,276K.

Can anyone explain to me how these figures relate to each other?

Thanks

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1 Answer 1

up vote 4 down vote accepted

The following article should help to explain:

http://technet.microsoft.com/en-us/library/cc771273%28WS.10%29.aspx

The memory showing in task manager is the amount of physical memory in use by the process that cannot be shared with other processes.

The following should help explain Virtual Address Space:

http://msdn.microsoft.com/en-us/library/aa366912%28v=vs.85%29.aspx

Definitions from TechNet and MSDN:

Private Bytes (KB). The current size of memory committed to a worker process, which cannot be shared with other processes. This corresponds to Virtual Memory Size in Windows Task Manager.

Virtual Bytes (KB). The current size of the virtual address space for a worker process. This does not correspond to anything in Windows Task Manager.

Virtual Address Space: A virtual address does not represent the actual physical location of an object in memory; instead, the system maintains a page table for each process, which is an internal data structure used to translate virtual addresses into their corresponding physical addresses. Each time a thread references an address, the system translates the virtual address to a physical address.

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Thanks, I hadn't seen that before. I've updated the answer with the definitions (needs peer reviewing). However, I still don't really understand what Virtual Bytes represents. What is meant by 'Virtual Address Space'? –  UpTheCreek May 19 '11 at 8:49
    
Additional info added about Virtual Address Space. –  Rob May 19 '11 at 12:37
    
Thanks for the update Rob. Does anyone really understand this though? I don't think I do. For instance, if virtual addresses are just pointers to physical addresses, then what does the size of the 'the current size of the virtual address space' mean? –  UpTheCreek May 19 '11 at 13:53

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