1.  Explain the difference between internal and external
    fragmentation.

Internal fragmentation is the wasted space within each allocated block
because of rounding up from the actual requested allocation to the
allocation granularity.  External fragmentation is the various free
spaced holes that are generated in either your memory or disk space.
External fragmented blocks are available for allocation, but may be
too small to be of any use.


2.  The access bit in the PTE can be used to implement LRU page
    replacement.  In the absence of an access bit we can use the valid
    bit.  Describe how you could implement LRU page replacement using
    the valid bit in the PTE.

Mark all PTEs that are valid as invalid.  When a page fault occurs for
any page in memory, treat this as an access to the page.  (You could
keep track of which pages are in memory and which are on disk with a
separate memory structure).  Mark the page as valid and continue.
Then, when you are scanning the page table for access bits, you
instead look at the valid bits to determine if a page has been
accessed.


3.  Describe any problems one will encounter when trying to mix the
    notion of shared pages with an inverted page table implementation.

Inverted page table entries point to the process and virtual address
that contain the page.  If more than one process or virtual address
location share a physical page, then the inverted page table can't
point to all of them (unless you do something fancy, thus the
problem).


4.  Describe the difference between logical and virtual clusters.

Logical clusters are associated with the numbering of clusters on the
disk or volume.  Virtual clusters are associated with the offset
within a file.


5.  Describe the pros and cons of paging against the system versus
    paging against the process.

Paging against the process is good because it keeps each process
within its own little area and a renegade process can't affect other
processes.  Paging against the system is good because it allows a
process that really needs the space to consume memory as necessary and
run better.