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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.
In a computer using virtual memory, accessing the location corresponding to a memory address may involve many levels. In computing, a memory address is a reference to a specific memory location in memory used by both software and hardware. [1] These addresses are fixed-length sequences of digits, typically displayed and handled as unsigned ...
Diagram of relationship between the virtual and physical address spaces. In computing, a physical address (also real address, or binary address), is a memory address that is represented in the form of a binary number on the address bus circuitry in order to enable the data bus to access a particular storage cell of main memory, or a register of memory-mapped I/O device.
Address spaces are created by combining enough uniquely identified qualifiers to make an address unambiguous within the address space. For a person's physical address, the address space would be a combination of locations, such as a neighborhood, town, city, or country. Some elements of a data address space may be the same, but if any element ...
Linux tmpfs (previously known as shm fs) [6] is based on the ramfs code used during bootup and also uses the page cache, but, unlike ramfs, it supports swapping out less-used pages to swap space, as well as filesystem size and inode limits to prevent out-of-memory situations (defaulting to half of physical RAM and half the number of RAM pages ...
Some operating system kernels, such as Linux, divide their virtual address space into two regions, devoting the larger to user space and the smaller to the kernel. In current 32-bit x86 computers, this commonly (although does not have to, as this is a configurable option) takes the form of a 3GB/1GB split of the 4 GB address space, so kernel ...
In computer architecture, 31-bit integers, memory addresses, or other data units are those that are 31 bits wide. In 1983, IBM introduced 31-bit addressing in the System/370-XA mainframe architecture as an upgrade to the 24-bit physical and virtual, [ 1 ] and transitional 24-bit-virtual/ 26-bit physical, [ 2 ] [ 3 ] addressing in System/370 .
In a system using segmentation, computer memory addresses consist of a segment id and an offset within the segment. [3] A hardware memory management unit (MMU) is responsible for translating the segment and offset into a physical address, and for performing checks to make sure the translation can be done and that the reference to that segment and offset is permitted.