A student writes, but you can delete and move on if you are more interested in getting read for the exam on Wednesday:


     I have wondered this for a while, but while skimming through the parts
     of the book we will be reading, found that this is not a topic covered
     in our class. I understand this may be an extremely complex topic, but i
     was just wondering, how does permanent storage (IE, a harddrive/cdrom,
     etc) come into play? is it another implementation of the I/O system, or
     would it contain its own opcode in an ISA with a harddrive?

     << name withheld to protect the new graduate-to-be >>

Yup, it is not covered in the book, mainly because we didn't want to make the book so big that we could give you your BS degree as soon as you finished it!

Seriously, the real answer is it depends on the system. At the first level, the more sophisticated devices have more I/O device registers that allow communication with them in the same way that we communicate with the keyboard and screen. However, the more sophisticated devices also have additional electronics to do more sophisticated stuff. This is sometimes carried out by logic (a la chapter 3) and sometimes by a program using the ISA of a simpler microprocessor that is just dealing with the paricular I/O activity of that device.

Hope that helps.

Yale Patt