VMware Server v/s ESXi on SATA drive

Hi guys, I was analyzing the performance of ESXi and VMware Server with Windows XP as host as well as guest and came up with an interesting conclusion. The performance of VMware server was wayyyy better than VMware ESXi. I used Passmark Performance Test 7.0 for benchmarking. My analysis is as follows:

Host system was a Pentium 4 2.8 GHz/2GB/80 GB. Windows virtual machine had 512 MB RAM and 8 GB HD. While performing the test no other virtual machines were running. In this test, hard disk read, write, and random seek + RW were measured.The following graph shows clearly the difference between the disk mark of two hypervisors:

The average Disk Mark for this test was 609.68 for VMware Server and 231.22 for VMware ESXi. The reason for this vast difference is unknown, due in large part because there is no official documentation from VMware discussing differences in hard drive access methods between VMware ESXi and VMware Server. I wonder if anyone else came across such a scenario.

Note: One thing to keep in mind is that the scores here are relative, and they have no units.