A simple application which creates a StringBuffer and updates it (JProva.java) is running 3 time faster on windows machines than on solaris server using 1.4.2 or 1.5.0 beta2
It is faster on machines with a better cpu clock (no I/O in the testcase)
Even using a multithreaded version (Test.java) it is faster on Windows (1 P4) than Solaris x86 (2 cpu, virtual 4) when running 50 threads

HW OS java Cpu Mem 1 5 10 20 30 40 50
======================================================================================================================
V65x S10_55 1.4.2_04-b05 (C2) 2xIntelXeon3GHz - 5189 16075 32148 65817 100468 136357 173739
Oracle W2000SP3 1.4.1_02-b06 (C1) IntelXeon2.4GHz 768MB 2766 12078 23968 49922 78656 109719 144313


JProva.java

import java.io.*;

class JProva {
public static void main (String args[]) {
int max = 0;
long millis;

millis = System.currentTimeMillis();
for(int k = 0 ; k < 1000000; k++)
{
StringBuffer buffer = new StringBuffer(" ");
String a1 = "cgghghghghghhhhhgd";
String a2 = "12";
String a3 = "XXXXXXX";
String a4 = "";
String a5 = "";
String a6 = "-ggggggggggggg";
String a7 = "-";
String a8 = "ggggg-";
char c;
int i;
int j = 0;

String str = a1;
for(i=0; i<str.length(); ++i) buffer.setCharAt(j+i, str.charAt(i));
j += 20;
str = a2;
for(i=0; i<str.length(); ++i) buffer.setCharAt(j+i, str.charAt(i));
j += 20;
str = a3;
for(i=0; i<str.length(); ++i) buffer.setCharAt(j+i, str.charAt(i));
j += 20;
str = a4;
for(i=0; i<str.length(); ++i) buffer.setCharAt(j+i, str.charAt(i));
j += 20;
str = a5;
for(i=0; i<str.length(); ++i) buffer.setCharAt(j+i, str.charAt(i));
j += 20;
str = a6;
for(i=0; i<str.length(); ++i) buffer.setCharAt(j+i, str.charAt(i));
j += 20;
str = a7;
for(i=0; i<str.length(); ++i) buffer.setCharAt(j+i, str.charAt(i));
j += 20;
str = a8;
for(i=0; i<str.length(); ++i) buffer.setCharAt(j+i, str.charAt(i));

if (k==0) System.out.println(buffer);
}
System.out.print("Durata: ");
System.out.println((System.currentTimeMillis()-millis));

}

}

With -Xrunhprof profiling we see that 99% of the time is spent in the new StringBuffer and the StringBuffer.<init>

See details in performance.html (JProva with a graph) and StringBuffer-Performance.html (both tests) and all the java.cpu* logs from profiling

http://pluto.italy.sun.com/Case/COFACE/37134601/performance.html
http://pluto.italy.sun.com/Case/COFACE/37134601/StringBuffer-Performance.html

Solaris:

java -server -Xrunhprof:cpu=y,file=java.cpu.loop.Test,depth=5 Test 50 prime

TRACE 13:
    Test$Work.test(Test.java:82)
    Test$Work.run(Test.java:73)
    java.lang.Thread.run(Thread.java:534)

TRACE 12:
    java.lang.StringBuffer.<init>(StringBuffer.java:115)
    java.lang.StringBuffer.<init>(StringBuffer.java:130)
    Test$Work.test(Test.java:82)
    Test$Work.run(Test.java:73)
    java.lang.Thread.run(Thread.java:534)

CPU SAMPLES BEGIN (total = 338182) Mon May 24 19:14:17 2004
rank self accum count trace method
   1 72.05% 72.05% 243645 13 Test$Work.test
   2 27.75% 99.79% 93837 12 java.lang.StringBuffer.<init>
   3 0.06% 99.85% 191 16 Test$Work.test
   4 0.05% 99.90% 178 15 Test$Work.test
   5 0.03% 99.93% 109 10 java.io.FileInputStream.readBytes
   6 0.03% 99.96% 88 17 Test$Work.test
   7 0.02% 99.98% 81 18 Test$Work.test
CPU SAMPLES END

Windows:

java -Xrunhprof:cpu=y,file=javaCpuTest.txt,depth=5 Test 50 prime

TRACE 7:
        Test$Work.test(Test.java:82)
        Test$Work.run(Test.java:73)
        java.lang.Thread.run(Thread.java:536)

TRACE 8:
        java.lang.StringBuffer.<init>(StringBuffer.java:115)
        java.lang.StringBuffer.<init>(StringBuffer.java:130)
        Test$Work.test(Test.java:82)
        Test$Work.run(Test.java:73)
        java.lang.Thread.run(Thread.java:536)

CPU SAMPLES BEGIN (total = 16788) Tue May 25 18:02:04 2004
rank self accum count trace method
   1 50.36% 50.36% 8455 8 java.lang.StringBuffer.<init>
   2 49.29% 99.65% 8274 7 Test$Work.test
   3 0.33% 99.98% 56 4 java.io.FileInputStream.readBytes
CPU SAMPLES END

where Test.java:82 is: buffer = new StringBuffer(" ");

Adding the test without hostspot we see that behaviour is similar on different Operating Systems

Running: java [-server] -XX:+PrintCompilation Test prime

Platform -client -server -Xint
----------------------------------------------------------------
Blade 2x1.2GHz 8257 7043 57703
x86 Linux P3-450Mhz 10042 7502 98358
x86 Win2k P3-550Mhz 8140 6578 74718
AMD =~ 2ghz 2672 ? 23829
Opteron Linux 2x1.4GHz 2403 2065 26491
v65xc-gmp02 3ghz? sol 5364 5185 21861

It seems that creation and initialization of StringBuffer is slower on Solaris hotspot than Windows hotspot