An area of confusion that seems to arise quite often is that around that of the Hyperthreading (HT) feature within ESX Virtual Infrastructure Client (VIC) being displayed as being ‘Inactive’.

Here is a link to Wikipedia that outlines what Hyperthreading is about and how it works.  This is another article with easy to follow information on the different CPU architectures.

If you see Hyperthreading within the VIC set to ‘Inactive’ you’re probably thinking “Hey, what’s going on here?  I’ve got a modern processor that can do this sorta stuff.”

Well, the answer is.. it depends.

If you have a single core processor and it is a Pentium 4 or early’ish (vague technical term ) Xeon then if it likely that you have Hyperthreading on the CPU’s die.  Sometimes it must be enabled in the BIOS first.  This article tells you what to look for.  Also, this list from Intel outlines which Intel processors and chipsets support Hyperthreading technology.

Hyperthreading disappeared from the Intel range of CPU’s with the introduction of the Merom, Conroe, and Woodcrest range of multi-core processors.

So if you are using a semi-recent PC/Server to run ESX then chances are you don’t have Hyperthreading technology on your CPU(s) and hence it is showing up as ‘Inactive’ within the Virtual Infrastructure Client.