On Jun 28, 5:56 pm, Charles Hooper <hooperc2..._at_yahoo.com> wrote:
> On Jun 28, 4:04 pm, zigzag..._at_yahoo.com wrote:
>
>
>
>
>
> > On Jun 28, 2:15 pm, sybra..._at_hccnet.nl wrote:
> > > On Thu, 28 Jun 2007 01:42:07 -0700, zigzag..._at_yahoo.com wrote:
> > > >When /3GB switch is turned on, will all oracle instances (5 in my
> > > >example) still have access only to 3GB memory combined or each
> > > >instance will have limit of 3GB memory. Various metalink articels say
> > > >this limit to be per instance so I am confused.
>
> > > They are discussing *virtual* memory, not *physical* memory. As soon
> > > as a system runs out of *physical* memory, it will swap memory it no
> > > longer needs to disk. When this memory is needed again it will be read
> > > from disk. This is called a page fault.
> > > A disk is a *slow* device.
> > > So, please, pray tell me, how desirable do you think it is to
> > > configure 3 Gb *per instance*?
>
> > > --
> > > Sybrand Bakker
> > > Senior Oracle DBA
>
> > If my server has 8GB physical meory, it will be nice to make use of
> > 8GB instead of restricted only to 3GB. I have seen
> > so many articles which talk about 3GB or 2GB per instance
> > restriction, but now I am told that is not correct, 3GB or 2GB
> > restriction is all instances combined, so it is confusing. Apparently
> > there is some restriction related to how much shared memory one can
> > allocate on Windows Server, otherwise each instance should be able to
> > address 2GB or 3GB (with /3GB switch).
>
> Google search:
> site:microsoft.com windows 2000 maximum memory
>
> Finds this web page:http://www.microsoft.com/whdc/system/platform/server/PAE/PAEmem.mspx
> "Operating systems based on Microsoft Windows NT technologies have
> always provided applications with a flat 32-bit virtual address space
> that describes 4 gigabytes (GB) of virtual memory. The address space
> is usually split so that 2 GB of address space is directly accessible
> to the application and the other 2 GB is only accessible to the
> Windows executive software.
>
> The 32-bit versions of the Windows 2000 Advanced Server and Windows NT
> Server 4.0, Enterprise Edition, operating systems were the first
> versions of Windows to provide applications with a 3-GB flat virtual
> address space, with the kernel and executive components using only 1
> GB. In response to customer requests, Microsoft has expanded the
> availability of this support to the 32-bit version of Windows XP
> Professional and all 32-bit versions of Windows Server 2003."
>
> http://msdn2.microsoft.com/en-US/library/aa196734(SQL.80).aspx
> "Windows NT 4.0 and Windows 2000 provide a 4-gigabyte (GB) virtual
> address space at any time, the lower 2 GB of which is private per
> process and available for application use. The upper 2 GB is reserved
> for system use. Windows NT Server, Enterprise Edition provides a 4-GB
> virtual address space for each Microsoft Win32® application, the lower
> 3 GB of which is private per process and available for application
> use. The upper 1 GB is reserved for system use.
>
> The 4-GB address space is mapped to the available physical memory by
> Windows NT Virtual Memory Manager (VMM). The available physical memory
> can be up to 4 GB, depending on hardware platform support."
>
> http://msdn2.microsoft.com/en-us/library/ms178067.aspx
> "The 32-bit operating systems such as Windows 2000 and Windows Server
> 2003 provide access to 4-gigabyte (GB) of virtual address space. The
> lower 2 GB of virtual memory is private per process and available for
> application use. The upper 2 GB is reserved for operating system use.
> All operating system editions, starting with Microsoft Windows XP
> Professional and later, including Windows Server 2003, include a
> boot.ini switch that can provide applications with access to 3 GB of
> virtual memory, limiting the operating system to 1 GB. See your
> Windows documentation for more information on using the /3GB switch
> memory configuration."
>
> >From "Microsoft Windows 95 Resource Kit" paperback version (c)1995
>
> page 976-977:
> "Windows 95 addresses this issue by using the 32-bit capabilities of
> the 80386 (and above) processor architecture to support a flat, linear
> memory model for 32-bit operating system functionality and Win32-based
> applications. A linear addressing model simplifies the development
> process for application vendors, and removes the performance penalties
> imposed by the segmented memory architecture.
>
> With this addressing model, Windows 95 allows full use of the 4 GB of
> addressable memory space for all 32-bit operating system components
> and applications. Each 32-bit application can access up to 2 GB of
> addressable memory space, which is large enough to support even the
> largest desktop application.
>
> The Memory Pager maps virtual addresses from the process's address
> space to physical pages in the computer's memory. In doing so, it
> hides the physical organization of memory from the process's threads."
>
> Hopefully, the above clarifies how memory is allocated on 32 bit
> Windows, which seems to be consistent all the way back to 1995.
>
> Charles Hooper
> IT Manager/Oracle DBA
> K&M Machine-Fabricating, Inc.- Hide quoted text -
>
> - Show quoted text -
Another useful link:
http://blogs.msdn.com/slavao/archive/2005/01/29/363181.aspx
Received on Sun Jul 01 2007 - 17:57:43 CDT
