CS560 Midterm Exam -- Answers and Grading
Question 4 -- 10 points
Answer
Translation Lookaside Buffer: A translation lookaside buffer is
a piece of associative memory (i.e. hardware) that caches virtual-to-physical
page translations so that frequent memory accesses can perform their
page translations without touching the page table in memory.
Interrupt Vector: The interrupt vector is a vector of program locations
that contain the operating system handlers for the various hardware interrupts
that can occur.
Direct Memory Access:
Direct Memory Access is where bytes are transferred directly from a device
to memory without using the CPU, thereby allowing the CPU to perform work
in parallel with the transfer.
Safe State: A safe state is one where there exists some ordering
of processes such that each process in that order can allocate its
maximum resource needs, then exit and free up resources for the next
process. If the system is always in a safe state, there can never be
deadlock.
Grading
Each question was worth 2.5 points. If your answer was more than two
sentences, you were docked half a point (it said one sentence, but I'll
be lenient with two). Here is what you had to say to get full credit:
- Translation Lookaside Buffer:
- 1 point for saying it was a piece of hardware (an associative memory
or cache is fine).
- 1 point for saying that it held virtual-to-physical memory translations.
- Interrupt Vector:
- 1 point for saying it defines where the OS gets control
- 1 point for saying it is indexed by interrupts
- Direct Memory Access:
- 1 point for saying that it transfers bytes directory from the device
to memory.
- 1 point for saying that it does so without affecting the CPU (or that
it only interacts with the CPU when it's finished via an interrupt).
- Safe State:
- 1 point for defining it correctly as one where there is an ordering
of processes that can complete.
- 1 point for mentioning (explicitly or implicitly) that the system
knows the processes' maximum resource needs.
- If you missed a point, you can get a half point for saying that you
can prevent deadlock by being in a safe state.
Points were deducted if you said incorrect stuff.