The EEPROM on a BrainStem module has a maximum 5ms write-cycle time.  While a write is in progress, no other memory access may take place.  If a VM program is executing a write operation, all other VM programs and reflex operations will halt until the write is completed.

Write operations eventually wear out an EEPROM chip.  The EEPROM on a BrainStem module has a guaranteed minimum of 100,000 write-cycles, though the actual cycles for an individual EEPROM may be much higher.  However, it is best to write to the EEPROM only when necessary.  The EEPROM should not be used as a space for frequent writing of temporary data.