Transcript INFO2006/ELEC 3030 The Data Link Layer

COMP1214
Systems & Platforms:
Operating Systems Concepts
Dr. Yvonne Howard – [email protected]
Rikki Prince – [email protected]
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Lessons from last sessions
• The main concerns of an OS
– Providing application developers
with an interface to use system
resources
– Managing the system resources
• How can devices communicate with
the OS?
• The separation of concerns among
– I/O devices, I/O device controllers
(hardware), Device drivers & OS
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Plan
• Identifying OS concepts
• Discuss individual concepts
– Establish relevance to OS concerns
OS concepts
Files
Processes
Memory mgmt
System calls
Relating concepts
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Discussion
• Are you familiar with the following
OS concepts? What are they?
– Files
– Processes
OS concepts
Files
Processes
Memory mgmt
System calls
Relating concepts
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Files
OS concepts
Files
Processes
Memory mgmt
System calls
Relating concepts
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Files
• path name
• root directory
• working directory
• special files
• pipes
OS concepts
Files
Processes
Memory mgmt
System calls
Relating concepts
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Discussion
• Have you seen the list of processes
running on:
- A windows environment?
- A UNIX environment?
OS concepts
Files
Processes
Memory mgmt
System calls
Relating concepts
• What types of processes can you see?
- Is it one process per application?
• What is the life-cycle of a process?
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Windows Task Manager
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Linux ps command
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Processor modes
• Processors can be running in
– Kernel mode
– User mode
OS concepts
Files
Processes
Memory mgmt
System calls
Relating concepts
• The processor enters kernel mode:
– At start-up, interrupt, error....
• The processor enters user mode:
– By an instruction (which sets the respective
register in the CPU)
• Certain instructions can only be executed in
kernel mode (privileged instructions)
– Accessing CPU registers
– Memory used by the kernel
– I/O
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Kernel mode-User mode in Win NT
OS concepts
Files
Processes
Memory mgmt
System calls
Relating concepts
SOURCE: support.novell.com
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Processes
• Multiprogramming
– More tasks than processors
– Processors switching between tasks
– Illusion of parallelism
OS concepts
Files
Processes
Memory mgmt
System calls
Relating concepts
• Scheduling
– Which task is next?
• One application requires one or
more such tasks (processes)
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Processes
• Each task/process can access
system resources
• Illusion of exclusive use of
OS concepts
Files
Processes
Memory mgmt
System calls
Relating concepts
– Memory (Address space)
– Storage
–…
• Can be notified of events by the
OS or other processes (signals)
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Discussion
• What is the use of each type of memory in the
hierarchy below?
• How is memory shared among processes?
• What if a program needs more memory than
available in RAM?
OS concepts
Files
Processes
Memory mgmt
System calls
Relating concepts
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Memory layout & Processes
Memory available per process?
ADDRESS SPACE
OS concepts
Files
Processes
Memory mgmt
System calls
Relating concepts
Memory needed larger than RAM?
VIRTUAL MEMORY
Process Table
Process Address Space
…
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Discussion
• Which concerns of an OS does each
of the following concepts relate to?
– Process
– Files
– Memory management
OS concepts
Files
Processes
Memory mgmt
System calls
Relating concepts
• How can the OS provide a clean
interface to the resources it
manages?
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Accessing system resources
• An OS provides applications with
APIs/libraries to access system
resources
OS concepts
Files
Processes
Memory mgmt
System calls
Relating concepts
– System calls can be invoked by applications
in user mode
– And are executed in kernel mode
• It is important that these are stable or
else applications have to be re-written
each time they change
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System calls
OS concepts
Files
Processes
Memory mgmt
System calls
Relating concepts
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OS concept map
OS concepts
Files
Processes
Memory mgmt
System calls
Relating concepts
p1
p2
CPU
p3
pN
Other
File System
File System
Other
System
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Other online resources
• CPU components and animation
– http://courses.cs.vt.edu/~csonline/MachineArchitecture/
Lessons/CPU/Lesson.html
• Computer architeture resources
(advanced)
– http://williamstallings.com/COA5e.html
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Lessons learned
• We are aware of the importance of OS
• We have introduced basic OS concepts
• We are familiar with the following concepts
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OS concepts
Files
Processes
Memory mgmt
System calls
Relating concepts
Processes
Address space
Files
Processor modes: Kernel mode/User mode
System calls
The UNIX Shell
• Textbook: sections 1.5-1.6
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next OS lectures:
• How can we deal with system resources
competing for CPU and Memory?
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Process scheduling
Memory management
File system
Virtual memory
• How can processors/computers be combined?
• How can a file system be reliable and secure?
• WHAT ABOUT SPECIFIC OPERATING SYSTEMS?
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