Search results
Results from the WOW.Com Content Network
File-backed mapping maps an area of the process's virtual memory to files; that is, reading those areas of memory causes the file to be read. It is the default mapping type. Anonymous mapping maps an area of the process's virtual memory not backed by any file, made available via the MAP_ANONYMOUS/MAP_ANON flags.
/dev/zero was introduced in 1988 by SunOS-4.0 in order to allow a mappable BSS segment for shared libraries using anonymous memory. [3] HP-UX 8.x introduced the MAP_ANONYMOUS flag for mmap(), which maps anonymous memory directly without a need to open /dev/zero. [4]
A memory-mapped file is a segment of virtual memory [1] that has been assigned a direct byte-for-byte correlation with some portion of a file or file-like resource. This resource is typically a file that is physically present on disk, but can also be a device, shared memory object, or other resource that an operating system can reference through a file descriptor.
The real advantage of MMFs is elegance and conciseness of code. For example, if you wanted to have a hash table, and have it in memory and yet also on disk (persistent), instead of writing a lot of code to manage both disk and memory, and then keep them in synch, you could use a MMF and safely just pretend the entire hash table was in memory ...
Memory-mapped file, also known as mmap() Memory-mapped I/O, an alternative to port I/O; a communication between CPU and peripheral device using the same instructions, and same bus, as between CPU and memory; Virtual memory, technique which gives an application program the impression that it has contiguous working memory, while in fact it is ...
This example may be clearer if memory is examined directly. Assume that a is located at address 0x8130 in memory and ptr at 0x8134; also assume this is a 32-bit machine such that an int is 32-bits wide. The following is what would be in memory after the following code snippet is executed:
Get AOL Mail for FREE! Manage your email like never before with travel, photo & document views. Personalize your inbox with themes & tabs. You've Got Mail!
Memory-mapped I/O is preferred in IA-32 and x86-64 based architectures because the instructions that perform port-based I/O are limited to one register: EAX, AX, and AL are the only registers that data can be moved into or out of, and either a byte-sized immediate value in the instruction or a value in register DX determines which port is the source or destination port of the transfer.