HW Systems Operating Systems COMP 101 Computational Thinking

HW & Systems: Operating Systems COMP 101 Computational Thinking and Design Tuesday, October 21, 2014 Carolyn Seaman Susan Martin 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: Virtual machine (OS): 1. Write program in binary 1. Write program using text 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 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

Operating Systems Schedule processes and pieces of processes Manage resources (data, I/O devices) Give users and programmers easier ways to make the computer work

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

It’s time for… OS Jeopardy!!!!!

Rules All questions and answers come from the assigned reading or the first part of this lecture I’ll show you an answer, you have to come up with the question If your team knows the question, one person needs to stand up If I call on your team, someone DIFFERENT from the person who stood up has to give the question If I call on your team, you must answer within 5 seconds No team can respond twice in a row

Answer: Operating system. Question: What does OS stand for?

Answer: A core component of the operating system that coordinates all other programs Question: What is the kernel?

Answer: One is static and written down, the other is dynamic and running. Question: What is the difference between a process and a program?

Answer: One has its own address space and the other shares an address space with other entities of the same type. Question: What is the different between a process and a thread?

Answer: It lets processes act as if there is more memory available than there actually is. Question: What is virtual memory?

Answer: When the kernel switches back and forth between programs, giving each its turn with the CPU. Question: What is multitasking?

Answer: Because it keeps users and programmers from having to think about the low-level hardware details of the computer they’re working with. Question: How is an OS an abstraction?

Answer: Process management, memory management, file system management, network and device management Question: What are the main functions of the kernel?

Answer: This occurs when all running processes have some resources (e. g. I/O devices), and are waiting for resources held by others. Question: What is deadlock?

Answer: If a process can’t get all the resources it needs, it must release all the resources it has and try again later. Question: How can you prevent deadlocks?

Answer: What the kernel does when a process’s time slice expires. Question: What is interrupt?

Answer: When a process is stuck waiting either for data or for a device to be available. Question: What is I/O bound?

Answer: When the kernel swaps out the context of one process for the context of another. Question: What is context switching?

Answer: round-robin, FIFO, priority-based, shortest-time-remaining Question: What are some scheduling policies that could be implemented by a kernel?

Answer: CPU utilization, average latency, throughput, fairness Question: What are some ways to measure the efficiency of the CPU?

Answer: A computer without an operating system. Question: What is a naked machine?