Deadlock - Revision history

Dmiyusov at 21:17, 20 November 2007

2007-11-20T21:17:37Z

← Older revision		Revision as of 21:17, 20 November 2007
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	~~'''Memory Management & Virtual Memory Lecture 10'''~~

	~~==Swapping==~~
	A memory management technique where a process may periodically have its primary memory space deallocated. This forces the swapped-out process to compete for memory before it can once again compete for the processor

	Swapping is especially well suited to timesharing systems since such systems often have times when a user logs onto the machine but is inactive for relatively long periods ( and hence not using the CPU).


	~~[[Image:Diagram1.jpg]]~~

	~~==Overlays==~~

	~~[[Image:diagram2.jpg]]~~



	~~Significant problem with overlays is when exactly do you load x, y or z. We have to make sure they are there. Developers need to think carefully what they put in these modules.~~
	Another problem with swapping is that x, y, and z can’t talk to each other , they need some sort of cut / paste buffer. The problem is that x, y and z are different sizes and we need to fit the biggest one in the overlay area.

	~~X,Y and Z are all desired to be loaded in the same area of RAM. In traditional overlay schemes this would be an index.~~

	~~Classic problem of memory management:~~
	~~Fragmentation, difference between size of overlay area and size of the overlays~~

	~~Instead of having one overlay area what if we had many?~~

	~~[[Image:Diagram3_c3.jpeg]]~~

	~~This is primitive because programming manually has to manage memory in addition to being inefficient. How do you deal with the situation so that you don’t need to deal with it every again?~~
	~~First step is to change this and to add relocation. To do that we need to have some sort of indirection~~


	~~[[Image:diagram4.jpg]]~~

	~~==Fragmentation==~~

	~~;'''Data fragmentation'''~~
	Reduces the amount of fragmentation in file systems. Occurs when a piece of data in memory is broken up into many pieces. Two types of fragmentation which exist are internal fragmentation and external fragmentation

	~~;'''Internal Fragmentation'''~~
	Space is wasted in return for increased efficiency or simplicity. An example is that many file systems files always start at the beginning of a sector, which simplifies organization and makes it easier to grow files. Any space that is left over between the last byte of the file and the first byte of the next sector is internal fragmentation. Internal fragmentation occurs when the index pages are not being used to their maximum volume

	~~;'''External Fragmentation'''~~
	~~In such a fragmentation, the free space which is available for storage is divided into many small pieces. The storage space is of many different sizes.~~

	~~;'''Page'''~~
	~~fixed-length block of main memory, that is contiguous in both physical addressing and virtual memory addressing.~~

	~~==Memory Segmentation==~~
	Technique used to divide memory into smaller units. It is an extension of the ideas suggested by the use of relocation-limit registers for relocating and bound checking blocks of memory. Memory contents are referenced using a two-component virtual address <segmentNumber, offset> .
	~~Segment number identifies the particular logical block of memory and offset is a linear offset from the beginning of the segment.~~
	Segmentation provides more programmer control over the units of transfer in the memory system than paging does. Memory segments are distinct from memory pages because the segments are usually much larger than pages, and can be of a variable size.

	~~==Paging==~~
	Thisis an allocation strategy in a paging system to reduce external fragmentation by transferring a fixed-size unit of virtual address space(page) whenever a virtual address in it is needed to execute the program. Every process’s virtual address space is logically divided into pages, with each page having the same number of location.

	The program translation image is constructed to fit in a set of G continguous memory locations, with virtual addresses ranging between 0 and G-1. When the process executes it is allocated enough primary memory to store the contents of H memory locations where H<G (that is the process has fewer physical memory locations than virtual addresses)

	In a binary computer the paging system maps the virtual addressees in the absolute module (0-G) into a set of n = 2^g pages, each of size c = 2^h. If G is not an integer multiple of the page size then part of the last page will be lost to internal fragmentation; the paging system will adjust G upward to hold the entire virtual address space.

	Physical address space is the portion of the primary memory allocated to the process. The units of allocation are page frames and these are blocks of primary memory which are the same size as the page. The physical address space can be though of as a set of m = 2^j page frames each of size c = 2^h, so the amount of primary memory allocated to the process is H = 2^(h+j)

	~~[[Image:The_address_space_and_pages.JPG]]~~


	~~==Paging Algorithms==~~
	~~There are two basic types of pagig algorithms: static and dynamic allocation~~



	~~===Static Paging algorithms===~~
	~~allocates a fixed number of page frames to a process when it is created. The paging policy defines how these page frames will be loaded and unloaded by the virtual memory system.~~

	~~Three basic policies in defining paging algorithm are~~

	~~'''fetch policy:'''~~
	~~when a page should be loaded into memory~~

	~~'''replacement policy:'''~~
	~~determines which page should be removed from primary memory if all page frames are full~~

	~~'''placement policy:'''~~
	~~determines where the fetched page whould be loaded into primary memory~~

	~~===Dynamic Paging algorithms===~~
	~~Dynamic paging algorithms adjust the memory allocation to match the process's needs as they change.~~

Dmiyusov at 21:14, 20 November 2007

2007-11-20T21:14:37Z

← Older revision		Revision as of 21:14, 20 November 2007
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	'''Memory Management & Virtual Memory Lecture 11'''		'''Memory Management & Virtual Memory Lecture 10'''

	==Swapping==		==Swapping==

Dmiyusov at 21:13, 20 November 2007

2007-11-20T21:13:49Z

← Older revision		Revision as of 21:13, 20 November 2007
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			'''Memory Management & Virtual Memory Lecture 11'''
	'''Memory Management & Virtual Memory'''

	==Swapping==		==Swapping==

Dmiyusov at 20:40, 18 November 2007

2007-11-18T20:40:26Z

← Older revision		Revision as of 20:40, 18 November 2007
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	'''Memory Management & Virtual Memory'''		'''Memory Management & Virtual Memory'''
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	===Static Paging algorithms===		===Static Paging algorithms===
	allocates a fixed number of page frames to a process when it is created. The paging policy defines ~~hwo tehse~~ page frames will be loaded and unloaded by the virtual memory system		allocates a fixed number of page frames to a process when it is created. The paging policy defines how these page frames will be loaded and unloaded by the virtual memory system.
	~~three~~ basic policies in defining paging algorithm are
			Three basic policies in defining paging algorithm are

	'''fetch policy:'''		'''fetch policy:'''
	when a page should be loaded into memory		when a page should be loaded into memory

Dmiyusov at 12:16, 13 November 2007

2007-11-13T12:16:59Z

← Older revision		Revision as of 12:16, 13 November 2007
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	~~'''(Currently UNDER CONSTRUCTION!)'''~~

	'''Memory Management & Virtual Memory'''		'''Memory Management & Virtual Memory'''

Dmiyusov at 03:21, 13 November 2007

2007-11-13T03:21:13Z

← Older revision		Revision as of 03:21, 13 November 2007
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	Instead of having one overlay area what if we had many?		Instead of having one overlay area what if we had many?

	[[Image:~~Diagram3_c2~~.~~JPG‎~~]]		[[Image:Diagram3_c3.jpeg]]

	This is primitive because programming manually has to manage memory in addition to being inefficient. How do you deal with the situation so that you don’t need to deal with it every again?		This is primitive because programming manually has to manage memory in addition to being inefficient. How do you deal with the situation so that you don’t need to deal with it every again?

Dmiyusov: /* Static Paging algorithms */

2007-11-13T03:08:36Z

Static Paging algorithms

← Older revision		Revision as of 03:08, 13 November 2007
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	allocates a fixed number of page frames to a process when it is created. The paging policy defines hwo tehse page frames will be loaded and unloaded by the virtual memory system		allocates a fixed number of page frames to a process when it is created. The paging policy defines hwo tehse page frames will be loaded and unloaded by the virtual memory system
	three basic policies in defining paging algorithm are		three basic policies in defining paging algorithm are
	'''fetch policy'''		'''fetch policy:'''
	when a page should be loaded into memory		when a page should be loaded into memory

	'''replacement policy'''		'''replacement policy:'''
	determines which page should be removed from primary memory if all page frames are full		determines which page should be removed from primary memory if all page frames are full

	'''placement policy'''		'''placement policy:'''
	determines where the fetched page whould be loaded into primary memory		determines where the fetched page whould be loaded into primary memory

	===Dynamic Paging algorithms===		===Dynamic Paging algorithms===
	Dynamic paging algorithms adjust the memory allocation to match the process's needs as they change.		Dynamic paging algorithms adjust the memory allocation to match the process's needs as they change.

Dmiyusov: /* Static Paging algorithms */

2007-11-13T03:08:16Z

Static Paging algorithms

← Older revision		Revision as of 03:08, 13 November 2007
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	'''replacement policy'''		'''replacement policy'''
	determines which page should be removed from primary memory if all page frames are full		determines which page should be removed from primary memory if all page frames are full

	'''placement policy'''		'''placement policy'''

	determines where the fetched page whould be loaded into primary memory		determines where the fetched page whould be loaded into primary memory

	===Dynamic Paging algorithms===		===Dynamic Paging algorithms===
	Dynamic paging algorithms adjust the memory allocation to match the process's needs as they change.		Dynamic paging algorithms adjust the memory allocation to match the process's needs as they change.

Dmiyusov: /* Static Paging algorithms */

2007-11-13T03:07:56Z

Static Paging algorithms

← Older revision		Revision as of 03:07, 13 November 2007
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	three basic policies in defining paging algorithm are		three basic policies in defining paging algorithm are
	'''fetch policy'''		'''fetch policy'''

	when a page should be loaded into memory		when a page should be loaded into memory

	'''replacement policy'''		'''replacement policy'''
			determines which page should be removed from primary memory if all page frames are full

	~~determines which page should be removed from primary memory if all page frames are full~~
	'''placement policy'''		'''placement policy'''

Dmiyusov at 03:07, 13 November 2007

2007-11-13T03:07:07Z

← Older revision		Revision as of 03:07, 13 November 2007
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	allocates a fixed number of page frames to a process when it is created. The paging policy defines hwo tehse page frames will be loaded and unloaded by the virtual memory system		allocates a fixed number of page frames to a process when it is created. The paging policy defines hwo tehse page frames will be loaded and unloaded by the virtual memory system
	three basic policies in defining paging algorithm are		three basic policies in defining paging algorithm are
	1) fetch policy		'''fetch policy'''
	when a page should be loaded into memory
	2) replacement policy		when a page should be loaded into memory
	determines which page should be removed from primary memory if all page frames are full		'''replacement policy'''
	3) placement policy
	determines where the fetched page whould be loaded into primary memory		determines which page should be removed from primary memory if all page frames are full
			'''placement policy'''

			determines where the fetched page whould be loaded into primary memory

	===Dynamic Paging algorithms===		===Dynamic Paging algorithms===
	Dynamic paging algorithms adjust the memory allocation to match the process's needs as they change.		Dynamic paging algorithms adjust the memory allocation to match the process's needs as they change.