What is Ultra Direct Memory Access (Ultra DMA)?

An link that transmits data between a computer and a recording device (typically a hard disk) is called Ultra DMA, also known by the abbreviation UDMA. With a rapid transmission speed of up to 133 MB/s, it replaces Word DMA (or WDMA) as the quickest DMA variant. It enables direct data transfers from system memory, skipping the Processor and all related costs, just like all other forms of DMA.

Data is transferred by computers over the Parallel ATA link from a RAM to a hard drive using different DMA protocols. Hard drives must be attached using an 80-conductor ATA connection rather than a 40-conductor one due to the higher rates provided by most UDMA options. All of the additional lines in this wire are ground lines, which are placed between the data lines to reduce crosstalk.

To enable quicker data transmission speeds over WDMA, UDMA introduces two additional functions. First, double transition timing sends data twice rather than once per clock cycle. Second, cyclic redundancy checking (CRC) generates a CRC code along with the data and employs a method to determine duplicate data in a data transmission. In order to determine whether any data was damaged during the transmission, the recipient device compares the CRC code to the data received and, if required, asks that the data be sent again. In order to improve dependability, the system may transition to a sluggish UDMA option if CRC mistakes happen frequently.

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