In fibre-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single optical fibre by using different wavelengths (colours) of laser light to carry different signals. This allows for a multiplication in capacity, in addition to making it possible to perform bidirectional communications over one strand of fibre.
The term wavelength-division multiplexing is commonly applied to an optical carrier (which is typically described by its wavelength), whereas frequency-division multiplexing typically applies to a radio carrier (which is more often described by frequency). However, since wavelength and frequency are inversely proportional, and since radio and light are both forms of electromagnetic radiation, the two terms are closely analogous.
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The Word DMA (WDMA) interface was the fastest method used to transfer data between the computer (through the ATA controller) and an ATA device until UDMA. Single/Multiword DMA took over from PIO as the choice of interface between ATA devices and the computer. The WDMA interface is grouped into different modes.
The explanation for the difference between single and multiword DMA can be found in how the Intel DMA chip 8237 works. In single transfer mode only one word (16-bit) will be transferred between the device and the computer before returning control to the CPU and later it will repeat this cycle, allowing the CPU to process data while data is transferred.
In multiword transfer mode (Block mode) once transfer is begun it will continue until all words are transferred..........
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