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33 Cards in this Set
- Front
- Back
- 3rd side (hint)
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OS |
Layer of software that provides applications programs with a cleaner model of the computer (hardware) |
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First OS |
Invented in 1950s |
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OS in the 70s |
Unix and Apple dos |
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First Gen OS |
Vacuum tubes, programs hard wired or on punch cards, no OS |
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Transistors and batch systems |
Queue multiple jobs to execute, normally Fortran & COBOL on punch cards |
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ICs and multiprogramming |
Multiple jobs in each memory partition, CPU executes other jobs while waiting. No more tapes, it reads jobs from cards to disk. |
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CPU cycle |
Fetch, decode, execute |
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CPU caching |
Goal is to increase performance by copying information from slow storage to fast storage |
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Trap |
Instruction that switches from user mode to kernel mode and invoking a predefined function |
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Interrupts |
Device driver to controller to CPU, handles interrupt, then resumes |
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Direct memory access |
Device controller transfers bulk data to main memory without CPU |
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Kernel mode |
CPU is unrestricted, all instructions, memory i/o is allowed |
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How does the kernel do I/O? |
When the i/o finishes an operation, generate an interrupt, letting the os know if it's done or an error occurs |
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Monolithic kernel |
Entire os runs as a single program in kernel mode |
Faster but really hard to debug |
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Microkernels |
Only essential components in kernel, rest is implemented as system programs in user mode |
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Modular kernel |
Smaller kernel with modules, only loaded on demand |
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Context switching |
Saving a state of a process and then later restoring that state to give the illusion of multitasking. Normally when processes exceeds time slice |
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Asynchronous thread cancellation |
One thread manually terminates the target thread, but it can leave data in an undefined state |
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Deferred thread cancellation |
Controlling thread indicates the thread it wishes to cancel and uses flags to check for safe termination. |
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Reentrant function |
Functions that can be interrupted in the middle of an operation and then called again, finally the original function can finish executing |
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Race condition |
Output is dependent on the sequence or timing of other uncontrollable events such as context switching or scheduling |
Often a result of multiple processes or threads operating on a shared resource |
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Requirements to avoid race conditions |
No 2 processes may be simultaneously inside their critical sections. No assumptions be made about the speed or number of CPUs. No process running outside its critical region may block other processes. No process should have to wait forever to enter its critical section. |
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Deadlock |
Nothing useful happens |
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Livelock |
Form of starvation, something is happening but nothing useful |
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Arbitrator solution |
Parallelism, in which there is non-optimal use of resources |
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Random timeout problem? |
Prevents deadlocks but has a fairness problem |
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Resource hierarchy |
Partial order on resources, starvation is still possible and not practical for large numbers of resources |
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Semaphore |
Special integer variable used for signalling among processes. Can be locked by a thread and unlocked by any thread. |
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Condition variable |
Useful for implementing CS containing loops waiting for conditions. Can block threads while other threads does something to satisfy that condition |
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Bash script |
find . - type f - name "$1" - printf '%p%s\n' |sort - k 2 - n - t '' - r |head - 2 |awk '{x += $2; print $2} END |
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Print all lines in txt that are longer than 80 characters |
Cat file.txt |awk 'length($0) > 80' |
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Predicted burst equation |
P = a * b + (1-a) * p' |
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Deadlock conditions |
Mutual exclusion - resources are unshareable Hold and wait - a process holding at least one resource is waiting to acquire additional resource No preemption - a resource can only be released by the process holding it Circular wait - Cycle of processes |
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