Pos/355 Memory Management Memo. a+

interoffice memorandum

to: department manager

FROM: KENNETH GILLAND

SUBJECT: OPEN SOURCE/CLOSED SOURCE SYSTEMS

DATE: 11/25/2013

CC: IT DEPARTMENT HEAD

INtroduction

In this memo I shall compare the relative merits of two operating systems and the functions of virtual and physical memory contained therein.

Windows Vs mac

Both systems share many common traits, especially in the area of physical memory. Physical memory, also known as Random Access Memory, or RAM, is where the majority of necessary tasks are stored, and where they are ran from. Programs such as antivirus, firewalls, etc are operated from the part of the hard disc that contains RAM. Storing programs in RAM helps them open and run much faster than if you were to open them “cold’ from the program itself.

Virtual memory is where we find the real multiprocessing capabilities however. Virtual memory uses a system of paging and segmentation to temporarily store and retrieve files on command. Programs run in virtual memory share resources, such as the necessary program files to run the program, without allocating duplicate “pages” to the various programs. These pages come from main memory and are retrieved and returned as needed.

The major differences in virtual memory between the two operating systems are in the structure of the data itself. Windows utilizes a “tree” structure composed of available addresses, which are those not in use; reserved addresses that are set aside for other uses; and committed addresses which are used to initiate the processes of virtual memory. In a windows OS about half of the address space is available for virtual memory. So, on a 32 bit system you would have about 4 GB of virtual memory per process, and 2 GB would be available for use, with the rest reserved for the OS.

Mac virtual memory uses page tables to allocate file pages. These three level table contain a page directory, which is in main memory and points to a location in the page...