Once again there's stuff I understand and more stuff I really don't understand. I think the answer is: "This is not a 64-bit CPU, but I'm not 100% sure. Interesting /proc/cpuinfo is slightly different on the hostOS for VMware ESX Server, an odd proprietary cousin of Red Hat, and a CentOS5 x86 VM. here's the info from the host OS cpu processor : 0 vendor_id : GenuineIntel cpu family : 15 model : 4 model name : Intel(R) Xeon(TM) MP CPU 3.16GHz stepping : 1 cpu MHz : 3169.453 cache size : 1024 KB fdiv_bug : no hlt_bug : no f00f_bug : no coma_bug : no fpu : yes fpu_exception : yes cpuid level : 5 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss tm lm bogomips : 6330.77 Hmm. There's two processors in there with sockets for more. But I only see info for one CPU. and heres the info from the Guest processor : 0 vendor_id : GenuineIntel cpu family : 15 model : 4 model name : Intel(R) Xeon(TM) MP CPU 3.16GHz stepping : 8 cpu MHz : 3169.074 cache size : 1024 KB fdiv_bug : no hlt_bug : no f00f_bug : no coma_bug : no fpu : yes fpu_exception : yes cpuid level : 5 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss constant_tsc up pni ds_cpl bogomips : 6441.62