First implemented in the HSC50 hierarchical storage controller, the protocol quickly spread throughout the entire line of mass storage controllers built by DEC. The UDA50 is an implementation of MSCP built on a Unibus card; other implementations (for example, the RQDX) stretch down to the Q-bus and small, 5 megabyte disk drives and even diskettes.
Designed to minimize the amount of CPU involvement, the protocol depends upon two queues. Into one queue are placed packets which fully describe the commands to be executed by the mass storage subsystem. To initiate an I/O request, the CPU has only to create a small data structure in memory, append it to a "send" queue, and if that is the first packet in the send queue, wake the MSCP controller. After the command has been executed, an appropriate status packet is placed into the second queue to be read by the CPU.
Interrupts to the CPU (a costly operation) are not needed so long as further command packets remain in the command queue and the response queue is not in danger of over-flowing. I/O-space reads and writes to the MSCP controller, a less-expensive but still-costly operation, are similarly minimized.
Because MSCP packets were deliberately designed to resemble the packets exchanged on the VMScluster interconnects, it is a very inexpensive operation to ship storage requests around a VMScluster for remote execution; this greatly facilitates the creation of large-scale VMSclusters. The dependence upon in-memory packets and the minimization of interrupts and I/O-space reads and writes greatly facilitates remote operations.
Parallel ATA (PATA), originally AT Attachment, also known as IDE or Integrated Drive Electronics, is a standard interface designed for IBM PC-compatible computers. It was first developed by Western Digital and Compaq in 1986 for compatible hard drives and CD or DVD drives. The connection is used for storage devices such as hard disk drives, floppy disk drives, optical disc drives, and tape drives in computers.
The control unit (CU) is a component of a computer's central processing unit (CPU) that directs the operation of the processor. A CU typically uses a binary decoder to convert coded instructions into timing and control signals that direct the operation of the other units.
In computer architecture, a bus is a communication system that transfers data between components inside a computer, or between computers. This expression covers all related hardware components and software, including communication protocols.
In computing, a context switch is the process of storing the state of a process or thread, so that it can be restored and resume execution at a later point, and then restoring a different, previously saved, state. This allows multiple processes to share a single central processing unit (CPU), and is an essential feature of a multiprogramming or multitasking operating system. In a traditional CPU, each process - a program in execution - utilizes the various CPU registers to store data and hold the current state of the running process. However, in a multitasking operating system, the operating system switches between processes or threads to allow the execution of multiple processes simultaneously. For every switch, the operating system must save the state of the currently running process, followed by loading the next process state, which will run on the CPU. This sequence of operations that stores the state of the running process and the loading of the following running process is called a context switch.
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An operating system (OS) is system software that manages computer hardware and software resources, and provides common services for computer programs.
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libtorrent is an open-source implementation of the BitTorrent protocol. It is written in and has its main library interface in C++. Its most notable features are support for Mainline DHT, IPv6, HTTP seeds and μTorrent's peer exchange. libtorrent uses Boost, specifically Boost.Asio to gain its platform independence. It is known to build on Windows and most Unix-like operating systems.
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