1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Maximum RAM on 64-bit

Discussion in 'Windows XP' started by So Call Me Crazy, Jun 2, 2010.

  1. So Call Me Crazy

    So Call Me Crazy Flightless Bird

    What is the maximum RAM XP 64-bit will utilize? I know it's 3 GB on 32-bit,
    but...

    TIA
     
  2. John

    John Flightless Bird

  3. Mark Adams

    Mark Adams Flightless Bird

  4. Bob I

    Bob I Flightless Bird

    128 GB on XP-64 but 32-bit has 4 GB of address space, not 3.

    So Call Me Crazy wrote:

    > What is the maximum RAM XP 64-bit will utilize? I know it's 3 GB on 32-bit,
    > but...
    >
    > TIA
    >
     
  5. So Call Me Crazy

    So Call Me Crazy Flightless Bird

    Thanks to all!

    "So Call Me Crazy" wrote:
     
  6. Stefan Patric

    Stefan Patric Flightless Bird

    On Wed, 02 Jun 2010 09:17:07 -0700, So Call Me Crazy wrote:

    > What is the maximum RAM XP 64-bit will utilize? I know it's 3 GB on
    > 32-bit, but...


    Be aware that max addressable RAM is limited by hardware, too. That is,
    how much can be installed and recognized. For example, was upgrading a
    friend's old (10 years, at least) HP desktop with Windows ME on it to a
    more suitable OS. It had 2 RAM slots with one 128MB chip installed. The
    specs from HP said max RAM was 512MB (2 x 256M8) even though 32-bit can
    address 4GB. I put two old, but tested and working, 512MB compatible
    DIMMs in it for 1GB, but only 512 of it was recognized by the hardware.
    (Probably a BIOS limitation, but it had the latest BIOS available.) So,
    I put two 256MB chips in it, and it recognized 512MB. 512MB was a
    hardware limitation not an OS one.

    Just so you know...

    Stef
     
  7. Stefan Patric

    Stefan Patric Flightless Bird

    On Wed, 02 Jun 2010 13:51:37 -0500, Bob I wrote:

    > 128 GB on XP-64 but 32-bit has 4 GB of address space, not 3.


    Technically, yes. But only about 3.2 is available to the user. The
    balance is reserved exclusively for the System.

    Stef

    > So Call Me Crazy wrote:
    >
    >> What is the maximum RAM XP 64-bit will utilize? I know it's 3 GB on
    >> 32-bit, but...
    >>
    >> TIA
    >>
     
  8. Bob I

    Bob I Flightless Bird

    Stefan Patric wrote:

    > On Wed, 02 Jun 2010 13:51:37 -0500, Bob I wrote:
    >
    >
    >>128 GB on XP-64 but 32-bit has 4 GB of address space, not 3.

    >
    >
    > Technically, yes. But only about 3.2 is available to the user. The
    > balance is reserved exclusively for the System.
    >


    The variable amount of unused RAM is entirely dependant on the
    particular hardware installed on the particular computer. The OP stated
    that 3 GB was the limit and that is incorrect. As to 3.2 GB, once again
    that is NOT a limit, nor is it "reserved", it is used to comunicate with
    installed hardware. Remove or reconfigure hardware and the value will
    change. All you can say is that 3.2 GB is an approximate value for
    common pc configurations.
     
  9. Stefan Patric

    Stefan Patric Flightless Bird

    On Thu, 03 Jun 2010 07:39:24 -0500, Bob I wrote:

    > Stefan Patric wrote:
    >
    >> On Wed, 02 Jun 2010 13:51:37 -0500, Bob I wrote:
    >>
    >>
    >>>128 GB on XP-64 but 32-bit has 4 GB of address space, not 3.

    >>
    >>
    >> Technically, yes. But only about 3.2 is available to the user. The
    >> balance is reserved exclusively for the System.
    >>
    >>

    > The variable amount of unused RAM is entirely dependant on the
    > particular hardware installed on the particular computer. The OP stated
    > that 3 GB was the limit and that is incorrect. As to 3.2 GB, once again
    > that is NOT a limit, nor is it "reserved", it is used to comunicate with
    > installed hardware. Remove or reconfigure hardware and the value will
    > change. All you can say is that 3.2 GB is an approximate value for
    > common pc configurations.


    And that is why I said "about 3.2" meaning not exactly 3.2, but around
    3.2 or approximately 3.2. Even on a system with the barest of hardware,
    I myself have never seen more than about 3.35 available. Although, I've
    read claims of 3.5.

    Also, what would you call RAM that is exclusively accessible ONLY by the
    system for its use, that is, users or their apps can't access it? To me,
    that is the very definition of "reserved."

    Stef
     
  10. Paul

    Paul Flightless Bird

    Stefan Patric wrote:

    >
    > Also, what would you call RAM that is exclusively accessible ONLY by the
    > system for its use, that is, users or their apps can't access it? To me,
    > that is the very definition of "reserved."
    >
    > Stef


    That is not "reserved", it is "inaccessible" memory, since
    no mapping in the chipset decoders makes it possible to
    get to the memory locations in question. And I'm referring to
    processor access. When the processor sends an address over the
    FSB, the chipset maps the address to the appropriate piece of
    hardware. And in this case, where Windows indicates ~3.2GB
    free, it means 800MB of memory simple cannot be accessed from
    the processor. The memory continues to be refreshed by the DRAM
    controller (a function local to the Northbridge), and the
    Northbridge has visibility to the RAM, but the processor can't
    get there.

    *******

    For some interesting background on what might have been
    possible, try this article. PAE makes it possible, for a 32 bit
    OS to address a 36 bit or larger address space. Individual programs
    cannot use all the memory at once with that scheme - it would
    take multiple programs to be able to actually use all the memory,
    but PAE does offer a better alternative for someone who happens
    to buy too much memory for their computer. This person did some
    experiments, to show how easy it is to do.

    http://www.geoffchappell.com/viewer.htm?doc=notes/windows/license/memory.htm

    It is possible WinXP SP1 would have allowed this also. That is addressed
    in this section of that article.

    "Windows XP SP2

    Special mention must be made of Windows XP SP2 and SP3. If you were
    fortunate enough to have 4GB in a machine for running a client version
    of Windows up to and including Windows XP SP1, and your hardware had
    memory remapping so that some of your 4GB was above the 4GB address,
    and your third-party drivers worked correctly with memory above 4GB,
    then you will have faced an unfortunate side-effect when upgrading to
    Windows XP SP2: you will have bought a downgrade of how much RAM
    Microsoft permits you to use."

    If you wanted to use the entire 4GB, then your best bet would be
    WinXP SP1, rather than SP2 or SP3. Remapping should be turned on in
    the BIOS, if your BIOS doesn't automatically do the right thing.
    And that is for the x32 bit version of the OS, as x64 would be
    fine on its own.

    HTH,
    Paul
     
  11. Bob I

    Bob I Flightless Bird

    Stefan Patric wrote:
    > On Thu, 03 Jun 2010 07:39:24 -0500, Bob I wrote:
    >
    >
    >>Stefan Patric wrote:
    >>
    >>
    >>>On Wed, 02 Jun 2010 13:51:37 -0500, Bob I wrote:
    >>>
    >>>
    >>>
    >>>>128 GB on XP-64 but 32-bit has 4 GB of address space, not 3.
    >>>
    >>>
    >>>Technically, yes. But only about 3.2 is available to the user. The
    >>>balance is reserved exclusively for the System.
    >>>
    >>>

    >>
    >>The variable amount of unused RAM is entirely dependant on the
    >>particular hardware installed on the particular computer. The OP stated
    >>that 3 GB was the limit and that is incorrect. As to 3.2 GB, once again
    >>that is NOT a limit, nor is it "reserved", it is used to comunicate with
    >>installed hardware. Remove or reconfigure hardware and the value will
    >>change. All you can say is that 3.2 GB is an approximate value for
    >>common pc configurations.

    >
    >
    > And that is why I said "about 3.2" meaning not exactly 3.2, but around
    > 3.2 or approximately 3.2. Even on a system with the barest of hardware,
    > I myself have never seen more than about 3.35 available. Although, I've
    > read claims of 3.5.
    >
    > Also, what would you call RAM that is exclusively accessible ONLY by the
    > system for its use, that is, users or their apps can't access it? To me,
    > that is the very definition of "reserved."
    >


    I've seen anywhere from 2.7 to 3.7 available out of 4 GB. and it is the
    memory addresses that are being used not the memory itself. Give it
    up, you're clutching at straws.
     
  12. Tim Slattery

    Tim Slattery Flightless Bird

    Bob I <birelan@yahoo.com> wrote:

    >128 GB on XP-64 but 32-bit has 4 GB of address space, not 3.


    Yes, but that 4GB space is used to access video RAM, BIOS, and a few
    other things besides system RAM.

    --
    Tim Slattery
    Slattery_T@bls.gov
    http://members.cox.net/slatteryt
     
  13. Bob I

    Bob I Flightless Bird

    Yep, that dead horse has been tenderized

    Tim Slattery wrote:
    > Bob I <birelan@yahoo.com> wrote:
    >
    >
    >>128 GB on XP-64 but 32-bit has 4 GB of address space, not 3.

    >
    >
    > Yes, but that 4GB space is used to access video RAM, BIOS, and a few
    > other things besides system RAM.
    >


    Yep, that dead horse has been tenderized
     
  14. Stefan Patric

    Stefan Patric Flightless Bird

    On Fri, 04 Jun 2010 08:01:38 -0500, Bob I wrote:

    > Stefan Patric wrote:
    >> On Thu, 03 Jun 2010 07:39:24 -0500, Bob I wrote:
    >>
    >>
    >>>Stefan Patric wrote:
    >>>
    >>>
    >>>>On Wed, 02 Jun 2010 13:51:37 -0500, Bob I wrote:
    >>>>
    >>>>
    >>>>
    >>>>>128 GB on XP-64 but 32-bit has 4 GB of address space, not 3.
    >>>>
    >>>>
    >>>>Technically, yes. But only about 3.2 is available to the user. The
    >>>>balance is reserved exclusively for the System.
    >>>>
    >>>>
    >>>>
    >>>The variable amount of unused RAM is entirely dependant on the
    >>>particular hardware installed on the particular computer. The OP stated
    >>>that 3 GB was the limit and that is incorrect. As to 3.2 GB, once again
    >>>that is NOT a limit, nor is it "reserved", it is used to comunicate
    >>>with installed hardware. Remove or reconfigure hardware and the value
    >>>will change. All you can say is that 3.2 GB is an approximate value for
    >>>common pc configurations.

    >>
    >>
    >> And that is why I said "about 3.2" meaning not exactly 3.2, but around
    >> 3.2 or approximately 3.2. Even on a system with the barest of
    >> hardware, I myself have never seen more than about 3.35 available.
    >> Although, I've read claims of 3.5.
    >>
    >> Also, what would you call RAM that is exclusively accessible ONLY by
    >> the system for its use, that is, users or their apps can't access it?
    >> To me, that is the very definition of "reserved."
    >>
    >>

    > I've seen anywhere from 2.7 to 3.7 available out of 4 GB. and it is the
    > memory addresses that are being used not the memory itself. Give it
    > up, you're clutching at straws.


    Based on Paul's explanation making a distinction between "reserved" and
    "inaccessible," it seems the word "reserved" has special meaning to those
    who's vocation are computers other than how it is general used.

    Stef
     
  15. Paul

    Paul Flightless Bird

    Stefan Patric wrote:
    > On Fri, 04 Jun 2010 08:01:38 -0500, Bob I wrote:
    >
    >> Stefan Patric wrote:
    >>> On Thu, 03 Jun 2010 07:39:24 -0500, Bob I wrote:
    >>>
    >>>
    >>>> Stefan Patric wrote:
    >>>>
    >>>>
    >>>>> On Wed, 02 Jun 2010 13:51:37 -0500, Bob I wrote:
    >>>>>
    >>>>>
    >>>>>
    >>>>>> 128 GB on XP-64 but 32-bit has 4 GB of address space, not 3.
    >>>>>
    >>>>> Technically, yes. But only about 3.2 is available to the user. The
    >>>>> balance is reserved exclusively for the System.
    >>>>>
    >>>>>
    >>>>>
    >>>> The variable amount of unused RAM is entirely dependant on the
    >>>> particular hardware installed on the particular computer. The OP stated
    >>>> that 3 GB was the limit and that is incorrect. As to 3.2 GB, once again
    >>>> that is NOT a limit, nor is it "reserved", it is used to comunicate
    >>>> with installed hardware. Remove or reconfigure hardware and the value
    >>>> will change. All you can say is that 3.2 GB is an approximate value for
    >>>> common pc configurations.
    >>>
    >>> And that is why I said "about 3.2" meaning not exactly 3.2, but around
    >>> 3.2 or approximately 3.2. Even on a system with the barest of
    >>> hardware, I myself have never seen more than about 3.35 available.
    >>> Although, I've read claims of 3.5.
    >>>
    >>> Also, what would you call RAM that is exclusively accessible ONLY by
    >>> the system for its use, that is, users or their apps can't access it?
    >>> To me, that is the very definition of "reserved."
    >>>
    >>>

    >> I've seen anywhere from 2.7 to 3.7 available out of 4 GB. and it is the
    >> memory addresses that are being used not the memory itself. Give it
    >> up, you're clutching at straws.

    >
    > Based on Paul's explanation making a distinction between "reserved" and
    > "inaccessible," it seems the word "reserved" has special meaning to those
    > who's vocation are computers other than how it is general used.
    >
    > Stef


    It does. "Reserved" means the function is not documented. It may not
    rule out absolutely, the ability to access the thing. You may still be
    able to read or write a Reserved location.

    "Inaccessible" is more absolute, in that any attempt to use the resource
    will be repulsed by force (bus fault handler etc.). In this specific case,
    the problem is, there is no architectural connection, between some 800MB
    of memory locations, and the address bus on the processor. No 32 bit addresses
    sent by the processor, can get to those memory locations.

    If the processor is set up to use 36 bit addresses (i.e. PAE),
    then those locations could be accessed. They'd no longer be
    inaccessible, due to a decoding limitation.

    Compare these two chip specifications.

    Address 0x08 Reserved
    Address 0x04 Master_Reset
    Address 0x00 Device_ID

    versus this one

    Address 0x04 Master_Reset
    Address 0x00 Device_ID

    If I probe location 0x08 on the second chip, I get a bus fault ("Inaccessible").
    If I probe location 0x08 on the first chip, I get data, but I don't
    know what it does.

    I may be able to write to location 0x08 on the first chip, but since
    I don't know what the location does, the chip may go nuts as a result
    of me playing around. Engineers at the motherboard companies, spend
    part of their day, doing exactly that, to discover functions that
    Intel does not document. In that context, Reserved means "we're not
    telling you what this does" and it also means "we reserve the
    right to change what this register does, in any new revision of
    chip we release". The register may still happen to work, but
    only a fool would depend on it for some function. Some BIOS are
    written to access Reserved locations, at the peril of a new
    chip revision failing to work properly as a result. It means if the
    chip revision is changed, the motherboard design team has to
    re-test their hardware design again, for collateral damage.
    So fooling around with a Reserved resource, wastes engineering
    resources.

    Paul
     
  16. dennis

    dennis Flightless Bird

    On 05-06-2010 02:32, Paul wrote:

    > If the processor is set up to use 36 bit addresses (i.e. PAE),
    > then those locations could be accessed. They'd no longer be
    > inaccessible, due to a decoding limitation.


    Even PAE cannot solve it alone. Memory locations must be remapped. The
    overlap between MMIO and DRAM is usually solved by moving the overlapped
    DRAM up above 4G. PAE can then be used to get to it.
     
  17. Bob I

    Bob I Flightless Bird

    Stefan Patric wrote:

    > On Fri, 04 Jun 2010 08:01:38 -0500, Bob I wrote:
    >
    >
    >>Stefan Patric wrote:
    >>
    >>>On Thu, 03 Jun 2010 07:39:24 -0500, Bob I wrote:
    >>>
    >>>
    >>>
    >>>>Stefan Patric wrote:
    >>>>
    >>>>
    >>>>
    >>>>>On Wed, 02 Jun 2010 13:51:37 -0500, Bob I wrote:
    >>>>>
    >>>>>
    >>>>>
    >>>>>
    >>>>>>128 GB on XP-64 but 32-bit has 4 GB of address space, not 3.
    >>>>>
    >>>>>
    >>>>>Technically, yes. But only about 3.2 is available to the user. The
    >>>>>balance is reserved exclusively for the System.
    >>>>>
    >>>>>
    >>>>>
    >>>>
    >>>>The variable amount of unused RAM is entirely dependant on the
    >>>>particular hardware installed on the particular computer. The OP stated
    >>>>that 3 GB was the limit and that is incorrect. As to 3.2 GB, once again
    >>>>that is NOT a limit, nor is it "reserved", it is used to comunicate
    >>>>with installed hardware. Remove or reconfigure hardware and the value
    >>>>will change. All you can say is that 3.2 GB is an approximate value for
    >>>>common pc configurations.
    >>>
    >>>
    >>>And that is why I said "about 3.2" meaning not exactly 3.2, but around
    >>>3.2 or approximately 3.2. Even on a system with the barest of
    >>>hardware, I myself have never seen more than about 3.35 available.
    >>>Although, I've read claims of 3.5.
    >>>
    >>>Also, what would you call RAM that is exclusively accessible ONLY by
    >>>the system for its use, that is, users or their apps can't access it?
    >>>To me, that is the very definition of "reserved."
    >>>
    >>>

    >>
    >>I've seen anywhere from 2.7 to 3.7 available out of 4 GB. and it is the
    >> memory addresses that are being used not the memory itself. Give it
    >>up, you're clutching at straws.

    >
    >
    > Based on Paul's explanation making a distinction between "reserved" and
    > "inaccessible," it seems the word "reserved" has special meaning to those
    > who's vocation are computers other than how it is general used.
    >


    Have you ever seen a "Reserved" Sign? It means "set aside" just in case
    something "might need it". Memory addresses are assigned to hardware,
    they are being used, not "reserved", whether that hardware is a video
    card, USB port or RAM. Everybody just seems to get into a regular tizzy
    about the RAM assignments though.
     
  18. dennis

    dennis Flightless Bird

    On 07-06-2010 16:45, Bob I wrote:

    > Have you ever seen a "Reserved" Sign? It means "set aside" just in case
    > something "might need it". Memory addresses are assigned to hardware,
    > they are being used, not "reserved", whether that hardware is a video
    > card, USB port or RAM. Everybody just seems to get into a regular tizzy
    > about the RAM assignments though.
    >
    >


    It really depends on how you use the word "reserved" and in what context.

    To say that a part of the address space is reserved for other use than
    DRAM is very valid.
     
  19. Bob I

    Bob I Flightless Bird

    dennis wrote:
    > On 07-06-2010 16:45, Bob I wrote:
    >
    >> Have you ever seen a "Reserved" Sign? It means "set aside" just in case
    >> something "might need it". Memory addresses are assigned to hardware,
    >> they are being used, not "reserved", whether that hardware is a video
    >> card, USB port or RAM. Everybody just seems to get into a regular tizzy
    >> about the RAM assignments though.
    >>
    >>

    >
    > It really depends on how you use the word "reserved" and in what context.
    >
    > To say that a part of the address space is reserved for other use than
    > DRAM is very valid.


    Since those addresses aare already in use addressing the hardware, it is
    somewhat difficult to say they are "reserved" for other use?
     

Share This Page