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During Power-On-Self-Test (POST) code, a ROM image is copied from an ESCD sector of a read-only memory to an ESCD original buffer and an ESCD write buffer. Following the POST operations, the contents of the ESCD write buffer are copied to an ESCD runtime buffer. If a function to read or write ESCD is called from a protected mode, the segment descriptor is created from a protected mode base segment address typically termed an ESCD Selector parameter.If the ESCD runtime buffer is the same as the contents of the compared buffer or sector, a ROM flash it not performed. In addition, a function to read or write ESCD generates a pointer to the size of ESCD for determining an entry point into the ESCD.