...Memory Management in Mac OS Memory Management in Mac OS Mindfire Solutions www.mindfiresolutions.com March 6, 2002 Abstract: This paper discusses memory management by macintosh operating system. This paper is a summarized form of “Inside Macintosh: Memory” and is directed towards developers who are new to Mac development but had previous development experience on other operating system. After going through this article you will be familiar with memory architecture in Mac, ways to allocate and deallocate memory, using temporary memory, A5 world, heap management, heap zones, heap fragmentation and several other features provided by memory manager. MEMORY MANAGEMENT IN MAC OS.................................................................. 1 ORGANIZATION OF MEMORY IN MAC OS ......................................................... 3 The System Heap ..................................................................................................... 4 The System Global Variables................................................................................... 4 ORGANIZATION OF MEMORY IN AN APPLICATION PARTITION 1...................................... 4 The Application Stack 1........................................................................................... 6 The Application Heap 1........................................................................................... 6 The Application Global Variables and A5 World 1 .................................................
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...parts... http://www.ccleaner.com Run Disk Cleanup (Start>All Programs>Accessories>System Tools) check/tick all boxes, they're all safe to remove. Run Disk Defragmenter (Start>All Programs>Accessories>System Tools). Increase Virtual Memory... Open Computer Management, click Start, and then click Control Panel. Double-click Administrative Tools, and then double-click Computer Management. XP In the console tree, right-click Computer Management (Local), and then select Properties. On the Advanced tab, click Performance Options, and under Virtual memory, uncheck the check box of Automatically manage paging file size for all drives, click Change. In the Drive list, click the drive that contains the paging file you want to change (usually C:). Under Paging file size for selected drive, type a new paging file size (4095 for both) in the Initial Size and Maximum Size box, and then click Set. Click Apply and OK. Vista/Win 7 1.Open Control Panel>System and Maintenance>System. 2.In the left “Tasks”, click on 'Advanced System Settings'. 3.Click the “Advanced” tab. In “Performance” section, click on 'Settings' button. 4.Click on 'Advanced' tab. 5.In the “Virtual Memory” section, click on 'Change' button. 6.By default, “Automatically manage paging file size for all drives” setting is selected so that Windows Vista system can manage the paging file without user’s interruption. If you want change the paging file size,uncheck...
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...80386 MICROPROCESSOR It is a 32-bit microprocessor. It has 32 bit data bus and 32 bit address bus, so it can address up to 232 = 4GB of RAM. Features -Multitasking -Memory management -Software protection -Segmentation and paging -Large memory system(64Tbytes in virtual mode) Operating modes -Real mode -Protected mode -Virtual mode Internal architecture: There are 6 parallel functional units: -The bus unit: The bus interface unit provides a 32-bit data bus, a 32-bit address bus and control signals. 8-bit (byte), 16-bit (word) and 32-bit (double word) data transfers are supported. It has separate pins for its address and data bus lines. This processing unit contains the latches and drivers for the address bus, transceivers for the data bus, and control logic for signaling whether a memory input/output, or interrupt acknowledgement bus cycle is to be performed. -The prefetch unit: The prefetch unit performs a mechanism known as an instruction stream queue. This queue permits a prefetch up to 16 bytes (8 memory words) of instruction code which is used by the instruction decoder. Whenever bytes are loaded into the queue they are automatically shifted up through the FIFO to the empty location near the output. -The decode unit: It reads the machine-code instructions from the output side of the prefetch queue and decodes them into microcode instruction format...
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...The Benefits and Uses of Virtual Memory Marcia Amnay POS/355 Steven Kernan April 22nd, 2013 The Benefits and Uses of Virtual Memory This paper will discuss the benefits and uses of virtual memory. Programs require memory to start and run on computers. When several jobs are being processed at the same time, the operating system must keep track of how the computer’s memory and make sure there is enough. Computers come with a limited amount of random access memory which is known as RAM. RAM is the main memory on a computer. If a user is running multiple applications at the same time, the RAM on it will not be enough to execute the processes. This is when virtual memory comes in and balances the process. Virtual memory is a memory management technique. Virtual memory is secondary memory that can act as if it were part of the main memory. When the RAM is used up, virtual memory places data by using the hard disk or another disk of some kind for space. The hard disk is much slower then RAM so the more virtual memory used, the slower your computer will run. The computer will look for areas on the RAM that are not in use and copy it to the hard disk to free up space on the RAM. Virtual memory keeps ‘active’ process in the RAM and keeps the ‘inactive’ processes on the address space on the disk. When an ‘inactive’ process is needed, it will bring that process back to the RAM from the disk. This process is running in the background without the user being aware...
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...you prefer. 1. With a fresh system (reboot to make sure), dump the first 4 PTEs and analyze them (status bits, what VA->PA translation they do). 2. Find and dump the first 4 PTEs for the Tutor program and analyze them. The Tutor program starts at VA 50000. Find some PTEs for pages that have never been touched since system reset, above VA 50000, i.e. after Tutor. We can play with pages 0-20 or so without much worry about necessitating a reset, because these are left over from being bootstrap scratch memory. All the sensitive data is above 0x50000, including the interrupt vector table. 3. Set page 3 as valid but not yet referenced. Then do a read on it, check the PTE, then a write, check the PTE and interpret your findings. 4. Now set page 3 as invalid (not present) and try reads and writes. You see that nothing special has happened. That's because the PTE in the TLB is still showing the page as present, and the MMU checks the TLB before looking at memory PTs. 5. Writing a value in the CR3 registers flushes the TLB, i.e., makes it drop all its cache entries. This can be done using the Tutor register-set command. Use the same old CR3 value, of course, or expect to reboot, for example: "Tutor> rs cr3 51000". Do this and retry 4. You should see a page fault, exception 14. Use "rd all" to see CR2, the "linear address", which is the address that causes the page fault. Note on linear addresses (LAs): We have...
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...Memory Management Requirements Memory management requirement is important to operating systems. The memory management function is to manage the computer’s primary memory storage. Since all new computers and laptops run multiple programs at any one time, it is imperative to manage what programs can run in the main memory or RAM and which programs can be swapped to secondary memory storage. Using memory management techniques and virtual memory systems process can efficiently manage an operating system. The quality of these techniques or systems can have an extensive effect on the overall system performance of the operating system. Memory management methods such as single allocation, partitioned allocation, paged memory management, and segmented memory management are processes that are used to determine how memory is distributed through different processes. This process decides which program gets a space of the main memory, when the program can get the space, and how much memory space is available for each program. Single contiguous allocation is the easiest memory management method. The entire computer’s memory, except for the operating systems reserved memory, is available to a single application. Any operating system that uses single contiguous allocation can still multi-task by swapping the contents of memory to switch among applications. A partitioned allocation splits the main memory into multiple main memory partitions. In addition, each partition may contain information...
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...Markus Robinson Memory Management James Welti, Jr. POS/355 July 10, 2015 Memory Management And Its Requirements Memory management is the act of managing computer memory at the system level. The essential requirement of memory management is to provide ways to dynamically allocate portions of memory to programs at their request, and free it for reuse when no longer needed. Memory needs to be allocated to ensure a reasonable supply of ready processes to consume available processor time. Memory management also involves subdividing memory to accommodate multiple processes. This process, involving controlling and coordinating computer memory, assigns portions called blocks to various running programs. By doing this the overall system performance is optimized to its maximum performance. Memory management resides in hardware, the operating system, as well as in programs and applications. Within hardware, memory management involves components that physically store data. The components that are involved in memory management include random access memory (RAM) chips, memory caches, and flash-based solid-state drives (SSDs). As users demand change, memory management involves the allocation and ongoing reallocation of specific memory blocks to individual programs in the operating system. By combining two related tasks, known as allocation and recycling, application memory management ensures the availability of adequate memory for the objects and data structures of each running...
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...Memory Management Requirements POS/355 Introduction to Operating Systems March 3, 2014 Paul Rouk Introduction The main memory of a computer is divided into two categories; the operating system and programs that are currently being executed. Memory management itself is the task of subdivision. There are also four basic requirements to memory management which include; relocation, protection, sharing, logical organization and physical organization. Relocation Main memory is generally shared among a number of various processes. Since programmers cannot know in advance what other programs will be using the main memory when their program is executed thus creates the need for having the ability to swap processes in and out of the main memory. During swapping it is possible that the memory may be placed within different memory regions. Protection Each process should be protected against unwanted interference by other processes. This means programs in other processes should not be able to reference memory locations in a process for reading or writing purposes without permission. Since the operating system is unable to anticipate all of the memory references that a program will make it is important; the hardware rather than the software must satisfy the memory protection requirements. Sharing When it comes to sharing the protection mechanism must have the flexibility to allow several processes to access the same portion of the main memory. The memory management system...
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...Memory Management Requirements Main memory is an important part in a computer system because the operating system and many user applications must input into the main memory before the execution stage begins. The effectiveness of memory management affects the efficiency of the computer system. Efficient amount of memory must be obtainable to reduce the quantity of processor idle time while the computer’s devices are arranging to react. Effect memory management consists of a series of important requirements, which are relocation, protection, sharing, logical and physical organization. Relocation Once a source code is translated into an object code, there is no indication were loading of the code will occur when a program asks for it to execute. The code may even reside in a different portion of the memory every time the run is executed (Stallings, 2012). Program occasionally will switch in and out of memory and reside in different physical locations at different times. Physical addresses to the instructions and data values in programs are impossible to assign by the translator. Precise physical addresses must be located once the program code and data are loaded by the processor and operating system (Stallings, 2012). Memory management decides where instructions and data are located and relocation is a method of changing the logical address to physical address (AW-BC, 2013). Protection Once two programs occupy memory simultaneously, the programs can interfere with each other...
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...Memory management requirements can be broken up into five different sections: Relocation, Protection, Sharing, Local organization, and Physical organization. Many online resources confirm these exact requirements and seem to have the same information published so it is difficult to find something unique. It will be necessary to use information from the referenced textbook to explain memory management requirements. In a multiprogramming system, relocation is the act of moving a process into different areas of memory from which it began. To maximize efficiency, processes move into and out of main memory. Relocation therefore is essential for moving the process into available memory while keeping the memory reference information up to date. Protection of memory is best understood as preventing unwanted access to processes resident in memory and allowing authorized access only to the level allowed when permission is granted. It is important to understand that the physical processor and not the operating system is responsible for protecting memory since the operating system cannot always be scanning for memory reference violations (Stallings, 2012). Sharing capabilities are essential to reduce the amount of wasted or duplicated data in memory. Stallings stated, “The memory management system must therefore allow controlled access to shared areas of memory without compromising essential protection” (p. 309). In addition, shared memory is one of the fastest methods used for interprocess...
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...What is AMD’s Heterogeneous System Architecture? By Ralph Efftien Polytechnia Institute CGS-1280C Computer Hardware Berkeley Open Infrastructure for Network Computing (BOINC) evolved from the SetiAtHome screensaver program created by Dr. David Anderson at University of California – Berkeley. BOINC over the major revisions has gone from running scientific applications during a CPUs idle time to also running the apps on the GPU (BOINC, 2013). They first started with NVIDIA’s CUDA routines and added ATI’s CAL routines to enable projects applications to perform scientific calculations on their various GPUs. With the acquisition of ATI by AMD, AMD has since dropped support for the CAL routines and has gone with supporting OpenCL for running general applications of the graphics coprocessor. The following list are some of the projects that use the GPU: 1. http://einstein.phys.uwm.edu/ 2. http://boinc.thesonntags.com/collatz/ 3. http://milkyway.cs.rpi.edu/milkyway/ 4. http://boinc.fzk.de/poem/ 5. http://www.primegrid.com/ 6. http://setiathome.berkeley.edu/ 7. http://setiweb.ssl.berkeley.edu/beta/ 8. http://moowrap.net/ These projects are the first that use the GPU to perform calculations on work units. They all started with applications that BOINC ran CPUs and the programmers at the various projects then adapted to run on the GPU. BOINC being a multi-threaded program is able to run one project on each core of a systems CPU and anywhere...
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...Memory Management Requirements Effective memory management is vital for multiprogramming. The first goal of memory management is to pack in main memory as many processes as possible, and in order to meet this goal, there are five requirements a memory management system needs to satisfy. These requirements include the following: 1. Relocation In a multiprogramming system, the available main memory is shared among a number of processes. It is not possible for the programmer to know which programs will be already running in the memory while writing the code. In addition, swapping is important to move processes in and out of main memory to maximize processor utilization by providing a large pool of ready processes to execute. Once the program is swapped out to disk, it would be quite limiting to specify that when it is next swapped back in, it must be placed in the same memory region as before. Instead, we may need to relocate the process to a different area of memory. The operating system will need to know the location of process control information and the execution stack, as well as the entry point to begin execution of the program for this process. In addition, however, the processor must deal with memory references within the program. The processor hardware and the operating system software must be able to translate the memory references found in the code of the program into actual physical memory addresses, reflecting the current location of the program in the main memory...
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...computers need system memory to operate and require a method of management to insure the proper handling of the data stored within it. Memory management involves relocation, protection, sharing, logical organization, and physical organization of the data. Without proper memory management page faults would climb out of control and data could become corrupted or lost. As a process waits for its turn with the CPU the operating system may move the process out of the main system memory into the page file and back again into main memory. When it is moved around it may not be in the same memory address as it was before it was relocated. This is where memory management comes into play as it helps the operating system translates the memory references found in the processes code to the physical address of the program in the main system memory. Processes also need the protection from other processes for interfering with its operation. In this case process cannot access or reference memory addresses without permission. This is handled by the computers processor as the operate system cannot predict every memory reference that all running programs will make (Stallings, 2009). Sharing of system memory is another technique used by memory management. If you have many processes accessing the same program, allowing all processes to access the same memory address instead of requiring each process to have its own memory space will free up system memory. The part where memory management comes into play...
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...Memory Management Paper Gene Cotton POS/355 Terance Carlson 10/06/2014 The act of managing computer memory is known as memory management. This system is also known for allocating memory for certain programs as requested. Managing the memory properly is vital to any CPU system. If the there isn’t enough memory to run a program or application then the CPU may freeze or fail. There are two types of memory allocations systems that are commonly used Virtual Memory and Garbage Collection. Virtual Memory systems separate memory from physical addresses to distinguish between the amounts of RAM used efficiently through disk swapping. Basically the quality of the virtual manager can positively or negatively impact the overall CPU performance. The Garbage collection system is a distribution and or redistribution of the computer memory cores for a program or application. Usually this is maintained and managed at the programming level. The downside to Garbage collection is it may take up a large amount of total processing time and this also can affect the outcome of CPU performance. With memory management systems on multi-tasking operating systems the virtual memory programs must be able to be launched from different parts of the memory at any given time. So relocation is very important and is a requirement. The reason behind this is that when a program is closed or swapped back into memory it may not always be transitioned back to same place it came from. Most virtual memory...
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...What is Data Execution Prevention or DEP? A set of hardware and software technologies that perform additional checks on memory to help prevent malicious code from running on a system. What that means is it is basically the virus scanner of your memory looking for intrusions into your computer. DEP can be enforced by both hardware and software applications. Some of the major benefits are to help prevent code execution from data pages. How this is accomplished is by checking where the code is running this is done by software enforced DEP. Code is not typically executed from a default heap and the stack, this is how the software application can detect if there is code running from an inappropriate area. The first type of DEP we will talk about is the Hardware-enforced DEP. Hardware-enforced DEP marks all memory locations in a process as non-executable unless the location explicitly contains executable code. A class of attacks exists that tries to insert and run code from non-executable memory locations. DEP helps prevent these attacks by intercepting them and raising an exception. Hardware-enforced DEP relies on processor hardware to mark memory with an attribute that indicates that code should not be executed from that memory. DEP functions on a per-virtual memory page basis, and DEP typically changes a bit in the page table entry (PTE) to mark the memory page. Software enforced DEP is the other side of the coin. An additional set of Data Execution Prevention security...
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