1. A method for specifying concurrent execution of a string of I/O command blocks stored in a memory using only information in the string of I/O command blocks comprising: configuring one I/O command block in said string as a head of string concurrent I/O command block; configuring one I/O command block in said string as an end of string concurrent I/O command block; and configuring all other I/O command blocks in said string as concurrent skipped I/O command blocks wherein only information in the string of I/O command blocks is used to specify concurrent execution of said string of I/O command block.