Detachable processor module containing external microcode expansion memory

An electronic system comprising:

• a system circuit board including a first connector;
• a processing unit coupled to the system circuit board, the processing unit including
• a package,
• a processor circuit board substantially covered by the package, the processor circuit board including a second connector protruding from the package for attachment to the first connector,
• an embedded controller coupled to the processor circuit board at a first location and covered by the package, the embedded controller including an internal core memory having a microcode space to contain microcode, and
• an on-substrate memory unit coupled to the processor circuit board at a second location different than the first location and covered by the package, the on-substrate memory unit containing microcode executable by the embedded controller;
• and
• a system firmware attached to the system circuit board and in communication with the embedded controller and the on-substrate memory unit, the system firmware is accessed to initiate a boot procedure and includes at least one microcode instruction, which when executed by the embedded controller, allows the microcode located in the on-substrate memory unit to be read and executed by the embedded controller during a boot procedure.