UDMA

For the main article about the interface, see Parallel ATA.

The Ultra DMA (Ultra Direct Memory Access, UDMA) modes were the fastest method used to transfer data through the ATA hard disk interface, usually between the computer and an ATA device. UDMA succeeded Single/Multiword DMA as the interface of choice between ATA devices and the computer. There are eight different UDMA modes, ranging from 0 to 6 for ATA (0 to 7 for CompactFlash), each with its own timing.

80-conductor cable used for modes faster than UDMA 2 on the left compared to a 40-conductor cable

Modes faster than UDMA mode 2 require an 80-conductor cable to reduce data settling times, lower impedance and reduce crosstalk.^[1]

Transfer Modes

Mode	Number	Also called	Maximum transfer rate (MB/s)	Minimum cycle time	Defining standard
Ultra DMA	0		016.7	120 ns	ATA-4
	1		025.0	080 ns	ATA-4
	2	Ultra ATA/330	033.3	060 ns	ATA-4
	3[2]		044.4	045 ns	ATA-5
	4[2]	Ultra ATA/660	066.7	030 ns	ATA-5
	5[2]	Ultra ATA/100	100.0	020 ns	ATA-6
	6[2]	Ultra ATA/133	133.0	015 ns	ATA-7
	7	Ultra ATA/167	167.0	012 ns	CompactFlash 6.0[3]

See also

• PIO—The first interface type used between devices (mainly hard disks) and the computer.
• Parallel ATA
• Serial ATA

References

1. AT Attachment with Packet Interface - 7 Volume 2 - Parallel Transport Protocols and Physical Interconnect (ATA/ATAPI-7 V2) E.2.1.1 Cabling p172
2. 80-conductor cable required
3. CompactFlash 6.0 Introduction Archived 2010-11-21 at the Wayback Machine