![]() ![]() Instead, if the amount of free memory drops below a certain threshold, the system asks the running applications to free up memory voluntarily to make room for new data. Writable data is never removed from memory by the operating system. In iPhone applications, read-only data that is already on the disk (such as code pages) is simply removed from memory and reloaded from disk as needed. The portion of the disk that stores the unused data is known as the backing store because it provides the backup storage for main memory.Īlthough OS X supports a backing store, iOS does not. As memory gets full, sections of memory that are not being used are written to disk to make room for data that is needed now. To give processes access to their entire 4 gigabyte or 18 exabyte address space, OS X uses the hard disk to hold data that is not currently in use. Even for computers that have 4 or more gigabytes of RAM available, the system rarely dedicates this much RAM to a single process. In addition, OS X provides approximately 18 exabytes of addressable space for 64-bit processes. Both systems also provide up to 4 gigabytes of addressable space per 32-bit process. In order to properly tune your code though, you need to understand something about how the underlying system manages memory.īoth OS X and iOS include a fully-integrated virtual memory system that you cannot turn off it is always on. Minimizing memory usage not only decreases your application’s memory footprint, it can also reduce the amount of CPU time it consumes. Next Previous About the Virtual Memory SystemĮfficient memory management is an important aspect of writing high performance code in both OS X and iOS. ![]()
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