Ultra DMA
UDMA (abbreviation for Ultra Direct Memory Access ) is an access protocol of the ATA standard that specifies how data is transferred between the controller of an ATA hard disk and the main memory . It is a follow-up protocol to the PIO mode.
UDMA as well as DMA enable the hard disk to transfer data directly from or to the main memory using a DMA controller without using the processor. This relieves the system. With bus mastering , the hard disk controller itself takes on the task of a DMA controller. The different standards are UDMA33, UDMA66, UDMA100, UDMA133 etc. and indicate the theoretically achievable data transfer rate in MByte / s (MB / s).
UDMA33 made the start. To increase the transmission rate, the signal rate was doubled. This is possible because data is transmitted on both the rising and falling edges of the clock signal. This increased the data transfer from 33 MB / s to 66 MB / s initially.
In order to ensure the correctness of the data, a cyclical redundancy check (CRC check) was introduced with UDMA .
The UDMA mode is also often specified. The following equations apply here:
| UDMA | Transfer rate in MB / s |
designation |
|---|---|---|
| Mode 0 | 16.7 | UDMA16 |
| Mode 1 | 25.0 | UDMA25 |
| Mode 2 | 33.3 | UDMA33 |
| Mode 3 | 44.4 | UDMA44 |
| Mode 4 | 66.7 | UDMA66 |
| Fashion 5 | 100.0 | UDMA100 |
| Mode 6 | 133.3 | UDMA133 |
| Mode 7 | 166.0 | UDMA166 |
For transfer rates greater than 33.3 MB / s (i.e. from UDMA mode 3) a finer, 80-core flat ribbon cable is required, in which every second core is connected to ground, which better shields the signal cores from one another and makes the higher speed possible power. The connectors have as usual 40 poles, the host adapter -side connectors but has a special code to which the ATA - Host Adapter can see that such a cable is used. Only then does it enable the faster modes of greater than 33.3 MB / s. If you use the old, 40-wire cable, (some) BIOSes warn and refuse higher modes. In the case of 80-core cables, the connector at this end is blue to identify the end of the cable on the host adapter. When connecting the ATA / ATAPI devices with such a cable is therefore important to ensure that the blue end of the cable to the motherboard or the ATA - host adapter is connected.
For the meaning of the black and gray plugs on the ATA cable, see ATA cable: colors of the plugs .
See also
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- ↑ Ultra DMA (UDMA) modes from PCGuide.com
- ↑ Ernst Ahlers: Ultra-ATA / 66 doubles hard disk data rate. In: Heise online . February 19, 1998 . Retrieved January 2, 2018.