UDMA

UDMA ( abbreviation for Ultra Direct Memory Access) is an access log of the ATA standard that defines how data between the controller an ATA hard drive and the memory to be transferred. It is a follow-up protocol of the PIO mode.

UDMA DMA as well as allow the hard drive data using a DMA controller to transfer directly to and from the memory, without using the processor. Thus the system is relieved. In Bus Mastering the disk controller itself takes over the task of a DMA controller. The various standards are UDMA33, UDMA66, UDMA100, UDMA133, etc. and give the theoretically achievable data transfer rate in MB / s.

The first was UDMA33. To increase the transmission rate, the signal rate is doubled. This is possible because both the rising and the falling edges of the clock signal, data is transmitted. This data transfer increased from 33 MB / s on first 66 MB / s

To ensure the correctness of the data, has been introduced with UDMA Cyclic Redundancy Check ( CRC ).

Often UDMA mode is specified. Here are the following correspondences apply:

For transfer rates greater than 33.3 MB / s ( ie from UDMA mode 3 ) is a finer, 80-conductor ribbon cable necessary in the every second conductor is connected to ground, what the signal wires better shielding from each other and the higher speed only possible makes. The plugs have 40 poles as usual, but the host adapter - side plug has a special encoding, where the ATA host adapter can be seen that this type of cable is being used. Only then he will unlock the faster modes of larger 33.3 MB / s. It contains the old, 40 -wire cable is used, warn (some ) BIOSes and refuse higher modes. In the 80-conductor cables to identify the host adapter cable side end of the connector at this end is blue. When connecting the ATA / ATAPI device with such a cable is therefore important to ensure that the blue cable end is connected to the motherboard or the ATA host adapter.

For the meaning of the black and the gray connector on the ATA cable see ATA cable: color of the plugs.