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It then instructs the DMA hardware to begin the transfer. When the transfer is complete, the device interrupts the CPU. Scatter-gather or vectored I/O DMA allows the transfer of data to and from multiple memory areas in a single DMA transaction. It is equivalent to the chaining together of multiple simple DMA requests.
This kind of transfer is implemented as "single mode transfer" in the Intel 8237 DMA controller. In multiword transfer mode, once a transfer has begun it will continue until all words are transferred or the drive negates the DMA request line. This mode is implemented as "demand mode transfer" in the Intel 8237 DMA controller.
The first use of channel I/O was with the IBM 709 [2] vacuum tube mainframe in 1957, whose Model 766 Data Synchronizer was the first channel controller. The 709's transistorized successor, the IBM 7090, [3] had two to eight 6-bit channels (the 7607) and a channel multiplexor (the 7606) which could control up to eight channels.
moving large blocks of memory (e.g. string copy or DMA transfer) complicated integer and floating-point arithmetic (e.g. square root, or transcendental functions such as logarithm, sine, cosine, etc.) SIMD instruction s, a single instruction performing an operation on many homogeneous values in parallel, possibly in dedicated SIMD registers
In contrast, in direct memory access (DMA) operations, the CPU is uninvolved in the data transfer. The term can refer to either memory-mapped I/O (MMIO) or port-mapped I/O (PMIO). PMIO refers to transfers using a special address space outside of normal memory, usually accessed with dedicated instructions, such as IN and OUT in x86 architectures.
The Ultra DMA (Ultra Direct Memory Access, UDMA) modes are the fastest methods used to transfer data through the ATA hard disk interface, usually between a computer and an ATA device. UDMA succeeded Single / Multiword DMA as the interface of choice between ATA devices and the computer.
Parallel SCSI specifications include several synchronous transfer modes for the parallel cable, and an asynchronous mode. The asynchronous mode is a classic request/acknowledge protocol, which allows systems with a slow bus or simple systems to also use SCSI devices. Faster synchronous modes are used more frequently.
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