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The I/O request packet mechanism is also used by Digital Equipment Corporation's VMS operating system, and was used by Digital's RSX-11 family of operating systems before that. An I/O request packet in RSX-11 is called a directive parameter block, [ 1 ] as it is also used for system calls other than I/O calls.
A name used for asynchronous I/O in the Windows API is overlapped I/O. Input and output (I/O) operations on a computer can be extremely slow compared to the processing of data. An I/O device can incorporate mechanical devices that must physically move, such as a hard drive seeking a track to read or write; this is often orders of magnitude ...
A further complication is that a device traditionally considered an input device, e.g., card reader, keyboard, may accept control commands to, e.g., select stacker, display keyboard lights, while a device traditionally considered as an output device may provide status data (e.g., low toner, out of paper, paper jam).
Virtual device drivers represent a particular variant of device drivers. They are used to emulate a hardware device, particularly in virtualization environments, for example when a DOS program is run on a Microsoft Windows computer or when a guest operating system is run on, for example, a Xen host.
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.
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[4] [5] Linux kernels support AHCI natively since version 2.6.19, and FreeBSD fully supports AHCI since version 8.0. Windows Vista and Windows 7 also natively support AHCI, but their AHCI support (via the msahci service) must be manually enabled via registry editing if controller support was not present during their initial install.
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