ESXi

I have multiple hosts with Esxi 5.5 and 5.1. All CPU have IMC.

How can I see the current memory frequency on each host?

run this command

esxcli hardware memory get

For more details check this link

vSphere Documentation Center

this is a joke? this command does not provide information about IMC frequency.

VI client, hardware status.

IF you have vCenter and IF you are running the CIMs for your hardware vendor, then you should be able to see the capacity, type and speed of the memory in each slot in the Hardware Status tab. If you don't have vCenter, but you have the CIMs, you might be able to get the info from dmesg. Without the CIMs I don't see that info being available anywhere else.

On server with two Xeon E5620 processors, on Hardware Status tab i see: Memory "Speed: 1333 MHz"

but the specs, this processor only supports 800/1066 MHz memory:

ARK | Intel® Xeon® Processor E5620 (12M Cache, 2.40 GHz, 5.86 GT/s Intel® QPI)

any comments?

It may be too late, but

ssh:

cd /sbin

smbiosDump | more

thanks, this saved me cracking open the case prematurely.

This.  Search for Max Speed under the Memory Device Mapping sections.  (takes a bit of scrolling on my system to reach that part.