In certain rare circumstances, ESXi might detect that an application is interacting badly with the Pentium IV hyperthreading technology. (This does not apply to systems based on the Intel Xeon 5500 processor microarchitecture.) In such cases, quarantining, which is transparent to the user, might be necessary.

For example, certain types of self-modifying code can disrupt the normal behavior of the Pentium IV trace cache and can lead to substantial slowdowns (up to 90 percent) for an application sharing a core with the problematic code. In those cases, the ESXi host quarantines the virtual CPU running this code and places its virtual machine in the none or internal mode, as appropriate.