HebaJallad: /* Review Notes */

2017-11-04T04:59:49Z

Review Notes

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   - mmap: The virtual address range corresponds to the contents of a file or RAM.
   - Concurrency: More than one thing is happening at the same time.
 Creating a process:

Soma at 18:32, 31 October 2017

2017-10-31T18:32:01Z

← Older revision		Revision as of 18:32, 31 October 2017
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			==Video==

			The video from the lecture given on Oct. 31, 2017 [http://homeostasis.scs.carleton.ca/~soma/os-2017f/lectures/comp3000-2017f-lec14-31Oct2017.mp4 is now available].

	==Review Notes==		==Review Notes==

Ssarazin: Created page with "==Review Notes== Definitions: - OS: A resource Manager that abstracts the hardware so that applications can get easy access to it. The OS facilitates resource sharing amon..."

2017-10-28T21:38:46Z

Created page with "==Review Notes== Definitions: - OS: A resource Manager that abstracts the hardware so that applications can get easy access to it. The OS facilitates resource sharing amon..."

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==Review Notes==

Definitions:

- OS: A resource Manager that abstracts the hardware so that applications can get easy access to it. The OS facilitates resource sharing among concurrent programs.
- Kernel: The first program to launch when the computer boots. The kernel has absolute power over the hardware; it manages and controls access to these resources.
- Process: A running program. It has one or more threads and address space.
- Thread: A function that runs in the same memory space as other functions.
- Memory: A contiguous array of bytes. Modern systems virtualize memory, mapping it to physical memory so it can be shared among processes.
- Interrupts: A mechanism used by the kernel that interrupts the CPU when other tasks are higher priority.
- Signals: Inter-process communications. A mechanism used by the kernel and processes to communicate with one another.
- System Call: Specialized functions used by programs to request more resources from the kernel.
- File: A hierarchical name with a value mapping (Key/Value pair)
- Shell: Another program that is used to send system calls to the kernel or launch other programs.
- File system: A set of files grouped together with a common hierarchical root.
- Fragmentation: Variable sized memory allocation.
- Internal Fragmentation: Space wasted in an allocation.
- Concurrency: More than one thing happening at a time.
- Atomic Variables: Variables that guarantee a strict ordering of operations.
- Segmentation: Managing memory without paging.
- Segments: A variable sized block of memory that can be placed in different parts of the address space.
- Segfault: When a virtual address does not have a corresponding physical address.
- mmap: The virtual address range corresponds to the contents of a file or RAM.
- Concurrency: More than one thing is happening at the same time.

Creating a process:
* fork() creates a process and execve() loads the binary to the new process.
** returns a process id
*** pid > 0, parent process
*** pid < 0, error
*** pid = 0, child process

* When a parent does not deal with its child processes they become zombies
* If a parent dies before its children they become orphans that are re-parented by the OS

* wait()
** suspends the current process until one, some, or all of its children have terminated
** wait() can be called anytime to check on the status of children

IO redirection:
* >, direct to stdout
* <, direct to stdin
* |, connect the output of one process to the input of another process
* when a process starts it is given file descriptors to stdout, stdin, and stderr

Inodes:
* Contain information about the blocks corresponding to the contents of a file on disk, its owner, and the file access permissions.
* A filename points to an inode
* The inode count represents all of the files and folders on disk
* Hard links create another name to the same inode number
** Only point to files within the same file system
* Symbolic links are files with their own inode
** Can point to files in other partitions or file systems

Virtual Memory:
* Every process receives a memory map with virtual addresses that correspond to physical addresses.

Memory Allocation Challenges:
* Need to have a contiguous address range
* Data Structures can not be moved once allocated
* Memory is constantly allocated and deallocated

Solution to these challenges:
* Use fixed size chunks that can be stored anywhere
** Called a page in memory or a block on disk
** Sizes are always a power of 2 because addresses are indexed in bits
** The benefit: it removes the limitations on array sizes.
** Use a table to map virtual memory to physical memory -- called a page table
** In a 32 bit system: the top 20 bits are the page locations and the lower 12 bits are the page offset

Concurrency:
* Challenge: keeping the shared state consistent; want deterministic behavior from concurrent computations
* Solution: Need mechanisms that bypass the memory hierarchy.
** Use filesystem locking primitives -> atomic variables -> semaphores
** Use signals to synchronize the shared state

Segmentation:
* The physical address can be found by adding the segment register to the offset.

Operating Systems 2017F Lecture 14 - Revision history

HebaJallad: /* Review Notes */

Soma at 18:32, 31 October 2017

Ssarazin: Created page with "==Review Notes== Definitions: - OS: A resource Manager that abstracts the hardware so that applications can get easy access to it. The OS facilitates resource sharing amon..."