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Java Forum / General / December 2006JVM Sizing
Hi Is there a maximum amount of memory that can be addressed by the JVM and, if so, does it vary by JVM version? Regards > Hi > > Is there a maximum amount of memory that can be addressed by the JVM > and, if so, does it vary by JVM version? > > Regards Yes, there is a maximum. It varies by platform, I know. As far as I'm aware, it didn't change between 1.4.x and 1.5, and I don't think it has for 1.6. But what it is depends on the underlying architecture.  SignatureSteve W. Jackson Montgomery, Alabama > Yes, there is a maximum. It varies by platform, I know. As far as I'm > aware, it didn't change between 1.4.x and 1.5, and I don't think it has > for 1.6. But what it is depends on the underlying architecture. Do you know where this might be documented - I've not been able to find anything to date. Regards > > Yes, there is a maximum. It varies by platform, I know. As far as I'm > > aware, it didn't change between 1.4.x and 1.5, and I don't think it has [quoted text clipped - 4 lines] > > Regards First, let me qualify this by saying that I'm talking about the largest value that can be used with the -Xmx switch. Other respondents mention the JVM's default maximum heap size, which is not what I thought the original query wanted. I haven't seen any written documentation on the allowable values for this setting, but I have experimented with it because of questions and issues I've dealt with. So I know, for instance, that the Java mailing list for Mac developers has discussed it and concluded that the largest setting is 2108m. I don't recall the largest value in a Linux setting, but I've experimented on Windows XP and found that it's 1612m. I learned this using the command "java -Xmx####m" and playing a sort of high-low game until I got the maximum value. = Steve = SignatureSteve W. Jackson Montgomery, Alabama > Hi > > Is there a maximum amount of memory that can be addressed by the JVM > and, if so, does it vary by JVM version? It varies with the -Xmx commandline parameter. E.g. -Xmx 256m gives it 256 megs (a quarter gig). Usually enough for anything. >> Hi >> [quoted text clipped - 3 lines] > It varies with the -Xmx commandline parameter. E.g. -Xmx 256m gives it 256 > megs (a quarter gig). Usually enough for anything. Famous last words, like who could use more than 640K on a computer? Matt Humphrey matth@ivizNOSPAM.com http://www.iviz.com/ >>>Hi >>> [quoted text clipped - 5 lines] > > Famous last words, like who could use more than 640K on a computer? I'm not claiming it's "all you'll ever need", just that it's usually enough for *current* stuff. :) > Hi > > Is there a maximum amount of memory that can be addressed by the JVM > and, if so, does it vary by JVM version? > > Regards Well, a 32 bit JVM could address up to 4 GB of memory. A 64 bit JVM could address up to 2^34 GB of memory. SignatureTris Orendorff [Q: What kind of modem did Jimi Hendrix use? A: A purple Hayes.] >> Hi >> [quoted text clipped - 5 lines] >Well, a 32 bit JVM could address up to 4 GB of memory. A 64 bit JVM could >address up to 2^34 GB of memory. Why 2**34, that's only two bits more address space than the 4GB 32-bit version? -- Tim Slattery Slattery_T@bls.gov http://members.cox.net/slatteryt Tris Orendorff <triso@remove-me.cogeco.ca> wrote: >> Well, a 32 bit JVM could address up to 4 GB of memory. A 64 bit JVM could >> address up to 2^34 GB of memory. > Why 2**34, that's only two bits more address space than the 4GB 32-bit > version? 2^34 is substantially larger than 4. Both were in units of GB. - Lew >Tris Orendorff <triso@remove-me.cogeco.ca> wrote: >>> Well, a 32 bit JVM could address up to 4 GB of memory. A 64 bit JVM could [quoted text clipped - 4 lines] > >2^34 is substantially larger than 4. Both were in units of GB. 2**32 = 4,294,967,296. 2**34 = 17,179,869,184 or 4 times 2**32. substantially larger, yes, but 64-bit Windows systems, for example, implement a 37-bit address space which allows for 137,438,953,472 bytes (128GB). Far more than anybody today contemplates installing in their computer, but miniscule compared to an actual 64-bit address space. I just wondered why a 64-bit JVM expands the address space by only two bits? I agree there's no reason to go all the way to 64-bits at this point, but 34 bits doesn't seem reasonable to me. -- Tim Slattery Slattery_T@bls.gov http://members.cox.net/slatteryt >> Tris Orendorff <triso@remove-me.cogeco.ca> wrote: >>>> Well, a 32 bit JVM could address up to 4 GB of memory. A 64 bit JVM could [quoted text clipped - 13 lines] > bits? I agree there's no reason to go all the way to 64-bits at this > point, but 34 bits doesn't seem reasonable to me. Read it again. He said: 32 bits gives 4 GB (4 gibibytes, actually) 64 bits gives 2^34 GB (again, it should be GiB) 2^34 GiB = 16,777,216 tebibytes = 16,384 pebibytes = 16 exbibytes SignatureJohn W. Kennedy "The blind rulers of Logres Nourished the land on a fallacy of rational virtue." -- Charles Williams. "Taliessin through Logres: Prelude" > 32 bits gives 4 GB (4 gibibytes, actually) > 64 bits gives 2^34 GB (again, it should be GiB) > > 2^34 GiB = 16,777,216 tebibytes = 16,384 pebibytes = 16 exbibytes My one-year-old niece says things like "gibibytes", usually when we're baking cookies and she's visiting. Whoever came up with those ... words has managed the impossible: outdoing the Académie Française and won the Year's Most Boneheaded Top-Down Language-Engineering Attempt Award at the 2006 Chomskys, finally ending the illustrious French Academy's 370-year-long winning streak. Or would have, if they had Chomsky awards, and I were impaneled as a judge. (The Academy's suggested translation of "iPod" made it a very close thing, mind you.) P.S. Some references: http://netjmc.typepad.com/globally_local/2006/08/to_google_or_to.html http://techdirt.com/article.php?sid=20061215/003106 > Is there a maximum amount of memory that can be addressed by the JVM > and, if so, does it vary by JVM version? It depends on the JVM. But if you mean SUN Win32 32 bit JVM then the limit is about 1.5 GB. Arne Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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