Patent ID: 8051415

Claim:
A disk array apparatus which includes a plurality of disk apparatus and is connected to one or more host computers, and reads and writes data of said disk array apparatus based on an I/O instruction issued by said one or more host computers, comprising: a ROM which stores a first firmware; a CPU which carries out said first firmware; a RAM which stores said first firmware in a first storage area of physical address space, wherein said CPU carrying out said first firmware from said RAM such that said first firmware is executed from said RAM and not from said ROM prior to firmware exchange; and a TLB (Translation Look-aside Buffer) which is a buffer memory which belongs to said CPU, and stores information which makes said first storage area of physical address space of said RAM associated with a first logical area of logical address space, wherein said CPU has a function which, in case an instruction to exchange firmware and a second firmware are received, evacuates work data of said first firmware to an evacuation area, which is set in said RAM in advance, stores said second firmware in a second storage area of said physical address space of said RAM, updates said TLB to make said second storage area associated with said first logical area, and after that, makes said work data evacuated return from evacuation, and makes said second firmware continue to work with said work data, wherein said CPU carries out said second firmware from said RAM such that said second firmware is executed from said RAM and not from said ROM subsequent to firmware exchange, and wherein said first firmware is exchanged for said second firmware such that said second firmware becomes operable for said disk array apparatus without said second firmware having to be stored in said ROM.