It is strongly recommended that PEIMs perform only the minimum work to meet the requirements of the subsequence phase.
The PEI Foundation establishes the PEI Services Table that is usable by all PEIMs.
The PEI phase allows C-codes PEIMs to be executed prior to the availability of main memory. This is accomplished via configuring the on-CPU resources, such as the CPU data cache to be used as a memory call stack.