Quiz 2 Solutions

1. Use the hexadecimal codes in the left column to fill in the icon grid, assuming 1 bit per pixel.

   

   Icon

2. Suppose you work for a CPU manufacturer that has exhausted its supply of XOR gates. Show whether or not the following expression is equivalent to A⊕B by completing a truth table of all possible values of inputs A and B.

   A·B' + A'·B

   They are the same. Below is the truth table that proves it. You do not need to write the circuit diagram shown above the table – that’s just a convenient way to show how each column is calculated.

   

   Truth table

   Recall that XOR is a way to say “not equal to.” Its result is true when A and B are different.

3. In the memory hierarchy, what is the main difference between volatile and persistent memory?

   Some of you just stated the main organizing principle of the memory hierarchy: faster, smaller capacity vs. slower, larger capacity. That may be true, but the main difference is what happens when the power is cut.

   Volatile memory loses its content, while persistent memory retains it.