HW & Systems:
Operating Systems
IS 101Y/CMSC 101
Computational Thinking and Design
Tuesday, October 22, 2013
Marie desJardins
University of Maryland, Baltimore County
Wherefore OS?
 A “naked machine” has no tools or programs to help
the user
 Write instructions in binary
 Write data in binary
 Load instructions into memory one cell at a time
 Initiate program run
 Too difficult for humans to do
 We must build an interface to hide the details and make
the computer easier to build
 The OS is an abstraction of the machine that keeps
users and programmers from having to think about the
low-level hardware details
Virtual Machine (abstraction!)
Naked machine:
1. Write program in binary
2. Load instructions one-byone into memory
3. Insert start into memory
address 0 and push “go”
button
4. Read results from memory
one-by-one, in binary
Virtual machine:
1. Write program using text
editor in high-level language
2. Save program to folder
3. Use translator to convert to
binary
4. Use scheduler to load and
run
5. Use I/O system to print
results
UnQuiz
 What is the kernel? What are its main functions?
 What is the difference between a program, a process,
and a thread?
 What is multitasking?
 When does the kernel interrupt a running process?
 What is a context switch?
UnQuiz Part Two
 What are some possible process scheduling policies?
 What do these different ways of measuring CPU
efficiency mean?
 CPU utilization
 Average latency
 Throughput
 Fairness
 What is virtual memory?
Deadlock
 Safe use of resources: ensure that computer doesn’t get
stuck in deadlock
 Multiple programs requesting access to resources
 Deadlock occurs when all programs have some resources,
and are waiting for resources held by others
 Deadlock prevention: if you can’t get all resources, release
all you have and try again later
 Deadlock recovery: if no acknowledgement, send message
again
Midterm Review


Any grade change requests must be made in writing, with a clear
explanation of the error (e.g., addition or transcription problem) or reason
for regrade (e.g., an explanation of why you think your answer was a
reasonable one or should have received more partial credit)
“Another student got grade X” is not a justification for a grade change
unless you can clearly explain why your answer deserves that grade
Guest Lecture
Dr. Chuck LaBerge
Computer Engineering