Since modern hard disks have internal microprocessors, they also have internal
"software" that runs them. (Wouldn't it be neat if they had internal hard disks?
) These routines are what run the control logic and make the drive work. Of course
this isn't really software in the conventional sense, because these instructions are
embedded into read-only memory. This code is analogous to the system BIOS: low-level, hardware-based control
routines, embedded in ROM. It is usually called firmware, with the word
"firm" intending to connote something in between "hard" and
"soft". The functions that run the logic board's circuitry could be implemented
strictly with hardware devices, as was done with early drives. However, this would be
expensive and inflexible for today's sophisticated controllers, since it would make it
difficult to update or adapt the logic to match changes in hard disks or the devices they
interface with.
Much the way the system BIOS benefits from being in a changeable ROM chip that can be
modified relatively easily, the hard disk's firmware does as well. In fact, in many drives
the firmware can be updated under software control, very much the same way that a flash BIOS works. Unlike the system BIOS, this
is only very rarely done, when a particular sort of problem exists with the firmware logic
that can be fixed without requiring a physical hardware change. If you suspect that your
drive needs new firmware, check the drive manufacturer's web site. There you will find the
instructions that tell you if you need an update, and if so, how to accomplish it.
Next: Multiple Command Control and Reordering
