diff --git a/nsprpub/config/system-headers b/nsprpub/config/system-headers
index 7a2869e78421..cf0f11498f5f 100644
--- a/nsprpub/config/system-headers
+++ b/nsprpub/config/system-headers
@@ -6,6 +6,7 @@ bsd/syscall.h
 bstring.h
 builtin.h
 c_asm.h
+cf.h
 CFBundle.h
 CFData.h
 CFDictionary.h
@@ -54,6 +55,8 @@ machine/builtins.h
 machine/clock.h
 machine/endian.h
 machine/inline.h
+mach/mach_init.h
+mach/mach_host.h
 mach-o/dyld.h
 MacTypes.h
 Math64.h
@@ -105,6 +108,7 @@ support/TLS.h
 synch.h
 sys/atomic_op.h
 syscall.h
+sys/cfgodm.h
 sys/file.h
 sys/filio.h
 sys/immu.h
diff --git a/nsprpub/pr/include/prsystem.h b/nsprpub/pr/include/prsystem.h
index 0dc420b8df16..b0dfcf9e0905 100644
--- a/nsprpub/pr/include/prsystem.h
+++ b/nsprpub/pr/include/prsystem.h
@@ -116,6 +116,22 @@ NSPR_API(PRInt32) PR_GetPageShift(void);
 */
 NSPR_API(PRInt32) PR_GetNumberOfProcessors( void );
 
+/*
+** PR_GetPhysicalMemorySize() -- returns the amount of system RAM
+**
+** Description:
+** PR_GetPhysicalMemorySize() determines the amount of physical RAM
+** in the system and returns the size in bytes.
+**
+** Parameters:
+**   none
+**
+** Returns:
+**   The amount of system RAM, or 0 on failure.
+**
+*/
+NSPR_API(PRUint64) PR_GetPhysicalMemorySize(void);
+
 PR_END_EXTERN_C
 
 #endif /* prsystem_h___ */
diff --git a/nsprpub/pr/src/misc/prsystem.c b/nsprpub/pr/src/misc/prsystem.c
index 898cc3ceb868..89986d483d79 100644
--- a/nsprpub/pr/src/misc/prsystem.c
+++ b/nsprpub/pr/src/misc/prsystem.c
@@ -1,4 +1,4 @@
-/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
 /* ***** BEGIN LICENSE BLOCK *****
  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
  *
@@ -38,6 +38,7 @@
 #include "primpl.h"
 #include "prsystem.h"
 #include "prprf.h"
+#include "prlong.h"
 
 #if defined(BEOS)
 #include <kernel/OS.h>
@@ -45,6 +46,7 @@
 
 #if defined(OS2)
 #define INCL_DOS
+#define INCL_DOSMISC
 #include <os2.h>
 /* define the required constant if it is not already defined in the headers */
 #ifndef QSV_NUMPROCESSORS
@@ -60,8 +62,14 @@
 #include <sys/sysctl.h>
 #endif
 
+#if defined(DARWIN)
+#include <mach/mach_init.h>
+#include <mach/mach_host.h>
+#endif
+
 #if defined(HPUX)
 #include <sys/mpctl.h>
+#include <sys/pstat.h>
 #endif
 
 #if defined(XP_UNIX)
@@ -69,6 +77,29 @@
 #include <sys/utsname.h>
 #endif
 
+#if defined(AIX)
+#include <cf.h>
+#include <sys/cfgodm.h>
+#endif
+
+#if defined(WIN32)
+/* This struct is not present in VC6 headers, so declare it here */
+typedef struct {
+    DWORD dwLength;
+    DWORD dwMemoryLoad;
+    DWORDLONG ullTotalPhys;
+    DWORDLONG ullAvailPhys;
+    DWORDLONG ullToalPageFile;
+    DWORDLONG ullAvailPageFile;
+    DWORDLONG ullTotalVirtual;
+    DWORDLONG ullAvailVirtual;
+    DWORDLONG ullAvailExtendedVirtual;
+} PR_MEMORYSTATUSEX;
+
+/* Typedef for dynamic lookup of GlobalMemoryStatusEx(). */
+typedef BOOL (WINAPI *GlobalMemoryStatusExFn)(PR_MEMORYSTATUSEX *);
+#endif
+
 PR_IMPLEMENT(char) PR_GetDirectorySeparator(void)
 {
     return PR_DIRECTORY_SEPARATOR;
@@ -231,3 +262,101 @@ PR_IMPLEMENT(PRInt32) PR_GetNumberOfProcessors( void )
 #endif
     return(numCpus);
 } /* end PR_GetNumberOfProcessors() */
+
+/*
+** PR_GetPhysicalMemorySize()
+** 
+** Implementation notes:
+**   Every platform does it a bit different.
+**     bytes is the returned value.
+**   for each platform's "if defined" section
+**     declare your local variable
+**     do your thing, assign to bytes.
+** 
+*/
+PR_IMPLEMENT(PRUint64) PR_GetPhysicalMemorySize(void)
+{
+    PRUint64 bytes = LL_ZERO;
+
+#if defined(LINUX) || defined(SOLARIS)
+
+    long pageSize = sysconf(_SC_PAGESIZE);
+    long pageCount = sysconf(_SC_PHYS_PAGES);
+    LL_I2L(bytes, pageSize * pageCount);
+
+#elif defined(HPUX)
+
+    struct pst_static info;
+    int result = pstat_getstatic(&info, sizeof(info), 1, 0);
+    if (result == 1)
+        LL_I2L(bytes, info.physical_memory * info.page_size);
+
+#elif defined(DARWIN)
+
+    struct host_basic_info hInfo;
+    mach_msg_type_number_t count;
+
+    int result = host_info(mach_host_self(),
+                           HOST_BASIC_INFO,
+                           (host_info_t) &hInfo,
+                           &count);
+    if (result == KERN_SUCCESS)
+        LL_I2L(bytes, hInfo.memory_size);
+
+#elif defined(WIN32)
+
+    /* Try to use the newer GlobalMemoryStatusEx API for Windows 2000+. */
+    GlobalMemoryStatusExFn globalMemory = (GlobalMemoryStatusExFn) NULL;
+    HMODULE module = GetModuleHandle("kernel32.dll");
+
+    if (module) {
+        globalMemory = (GlobalMemoryStatusExFn)GetProcAddress(module, "GlobalMemoryStatusEx");
+
+        if (globalMemory) {
+            PR_MEMORYSTATUSEX memStat;
+            memStat.dwLength = sizeof(memStat);
+
+            if (globalMemory(&memStat))
+                LL_UI2L(bytes, memStat.ullTotalPhys);
+        }
+    }
+
+    if (LL_EQ(bytes, LL_ZERO)) {
+        /* Fall back to the older API. */
+        MEMORYSTATUS memStat;
+        memset(&memStat, 0, sizeof(memStat));
+        GlobalMemoryStatus(&memStat);
+        LL_I2L(bytes, memStat.dwTotalPhys);
+    }
+
+#elif defined(OS2)
+
+    ULONG ulPhysMem;
+    DosQuerySysInfo(QSV_TOTPHYSMEM,
+                    QSV_TOTPHYSMEM,
+                    &ulPhysMem,
+                    sizeof(ulPhysMem));
+    LL_I2L(bytes, ulPhysMem);
+
+#elif defined(AIX)
+
+    if (odm_initialize() == 0) {
+        int how_many;
+        struct CutAt *obj = getattr("sys0", "realmem", 0, &how_many);
+        if (obj != NULL) {
+            PRUint64 kbytes;
+            LL_I2L(kbytes, atoi(obj->value));
+            LL_MUL(bytes, kbytes, 1024);
+            free(obj);
+        }
+        odm_terminate();
+    }
+
+#else
+
+    PR_SetError(PR_NOT_IMPLEMENTED_ERROR, 0);
+
+#endif
+
+    return bytes;
+} /* end PR_GetPhysicalMemorySize() */
diff --git a/nsprpub/pr/src/nspr.def b/nsprpub/pr/src/nspr.def
index 0549fd048d8e..bfcf527841f7 100644
--- a/nsprpub/pr/src/nspr.def
+++ b/nsprpub/pr/src/nspr.def
@@ -460,3 +460,9 @@ EXPORTS ;-
 		PR_GetAddrInfoByName;
 		PR_GetCanonNameFromAddrInfo;
 ;+} NSPR_4.4;
+;+
+;+NSPR_4.6 {
+;+	global:
+		PR_GetPhysicalMemorySize;
+;+} NSPR_4.5;
+
diff --git a/nsprpub/pr/src/nspr_symvec.opt b/nsprpub/pr/src/nspr_symvec.opt
index b6a132a8917d..d9ca566ecffe 100644
--- a/nsprpub/pr/src/nspr_symvec.opt
+++ b/nsprpub/pr/src/nspr_symvec.opt
@@ -41,7 +41,7 @@ case_sensitive=YES
 ! These replace stubs 49-52
 ! --------------------------------------------------------------------------
 ! Ident 2,8 introduced for NSPR 4.6.
-! PR_FindLibrary removed. Replaced by Stub49 (resurrected).
+! PR_FindLibrary removed. Replaced by PR_GetPhysicalMemorySize.
 ! --------------------------------------------------------------------------
 !
 SYMBOL_VECTOR=(PR_Accept=PROCEDURE)
@@ -133,7 +133,7 @@ SYMBOL_VECTOR=(PR_FD_ZERO=PROCEDURE)
 SYMBOL_VECTOR=(PR_FileDesc2NativeHandle=PROCEDURE)
 SYMBOL_VECTOR=(PR_FindFunctionSymbol=PROCEDURE)
 SYMBOL_VECTOR=(PR_FindFunctionSymbolAndLibrary=PROCEDURE)
-SYMBOL_VECTOR=(PR_VMS_Stub49=PROCEDURE)
+SYMBOL_VECTOR=(PR_GetPhysicalMemorySize=PROCEDURE)
 SYMBOL_VECTOR=(PR_FindSymbol=PROCEDURE)
 SYMBOL_VECTOR=(PR_FindSymbolAndLibrary=PROCEDURE)
 SYMBOL_VECTOR=(PR_FloorLog2=PROCEDURE)
diff --git a/nsprpub/pr/tests/system.c b/nsprpub/pr/tests/system.c
index b4a89a0a20db..e75a452071a0 100644
--- a/nsprpub/pr/tests/system.c
+++ b/nsprpub/pr/tests/system.c
@@ -75,6 +75,7 @@ PRIntn main(PRIntn argc, char **argv)
     PR_fprintf(output, "Host page size is %d\n", PR_GetPageSize());
     PR_fprintf(output, "Page shift is %d\n", PR_GetPageShift());
     PR_fprintf(output, "Number of processors is: %d\n", PR_GetNumberOfProcessors());
+    PR_fprintf(output, "Physical memory size is: %llu\n", PR_GetPhysicalMemorySize());
 
     return 0;
 }  /* main */