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Memory Management
POS/355
August 12, 2013
Cynthia Wood
Alicia Pearlman, Advanced Facilitator, University of Phoenix
August 12, 2013
Cynthia Wood
Alicia Pearlman, Advanced Facilitator, University of Phoenix

Memory management requirements deal with relocation of processes, protection of the memory accessed from a process, sharing of memory for multiple processes, logical organization of structural for memory, and physical location of memory. The common types of memory are main memory and secondary memory. Main memory separate into two parts, the operating system and the user portion of the memory. User portion of memory sectioned off to accommodate multiple processes, which are waiting for engagement. Managing memory in a multiprogramming system is extremely important and requires main memory, on the user’s side, to share among the processes. Process stored on the main memory waits for transfer to an I/O device. To get the most value and most use of the processor’s time, it may become necessary to swap processes in and out of the main memory, for those processes not in a Ready or Running state. “The requirements that memory management is intended to satisfy.” (2012, 306) If swapping does not occur, it wastes the processors maximum output. The event of swapping processes, the process is removed from its original location. Process replaced by another process is in a ready or running state. The original process requires suspension and returned when needed. It is unknown where the process returned to the main memory. Process can move around to different locations in the main memory for processing. The operating system is responsible for management of main memory and the processes within it. The protection of memory data is crucial, when the process access to memory is a concern. The processes access to memory protected from unwanted access, whether it is accidental or purposeful. The processes should not be able to access the memory locations without special permission. Once a process has fulfilled its instruction, it goes through a check to ensure only the allocated permissions of memory is available to that process. A process should not be able to access another processes memory unless it is authorized to do so. The processor is responsible for this portion of memory management. Sharing memory for multiple processes provides the ability for processes to access the same data structure for the multiple processes need. Protection of the memory has to be adjustable to allow the processes to have access to the data and ensure no unauthorized memory has been accessed or compromised during the sharing process. Main memory and secondary memory structured in a straightforward fashion. It consists of designated address spaces, which employs a sequence of bytes or words. This structure reflects closes to the way hardware in the computer structure. Software, however, is not constructed in the same way. The difference is that software uses modules that are “read only” or enabled for editing. The OS and hardware have to manipulate the process to use the process. Main memory and secondary memory is different each other in physical size and location. Main memory is the closest in location and provides fastest access to memory will be most costly. This type of memory does not retain the memory for permanent storage. Any processing of memory saved permanently moved and placed on a secondary source of memory. Secondary memory provides a slower access to memory, which, in this regard is cheaper cost wise. Secondary memory is usually not volatile. Secondary storage provides a resource of storage to place and store data and programs permanently. This does not lose the memory. This type of memory enables programs for copying from the secondary storage to the main memory for execution of the called upon process and data as needed for the process. The OS is responsible for this flow of memory between the two levels of memory; the main memory and the secondary memory. Virtual memory is a scheme treating secondary memory like main storage and is manipulated by OS. In virtual memory, memory referenced within a process referred by logical addresses translated into physical addresses at run time. This occurrence allows for pages or segments of a process are loaded into the main memory. The initial process instructions, known as the resident set, are loaded first. These instructions execute until it encounters a logical address not in the main memory, causing an access fault. At this point, the process produces an interrupt signal and places the process in a blocking state for later use. The OS is responsible for retrieving the next logical address referred to by the process. The OS calls the disk I/O read request. Request is issued and the OS brings the translated logical address to the main memory for processing. I/O interrupt issued returns the control back to the process in a Ready state to continue. In the meantime, the OS can dispatch another request during the time the previous I/O request performed. This process continues until finished or canceled.

References
Stallings, William. (2012). Operating Systems: Internals and Design Principles, Seventh Edition. 7(340-346). Retrieved from the University of Phoenix POS/355 class materials.