UDMA

The Ultra DMA (Ultra Direct Memory Access, UDMA) interface was the fastest method used to transfer data through the ATA controller, 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 8 different UDMA modes, ranging from 0 to 6 for ATA (0 to 7 for CompactFlash), each with its own timing.

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		16.7	120 ns	ATA-4
	1		25.0	80 ns	ATA-4
	2	Ultra ATA/33	33.3	60 ns	ATA-4
	3^[2]		44.4	45 ns	ATA-5
	4^[2]	Ultra ATA/66	66.7	30 ns	ATA-5
	5^[2]	Ultra ATA/100	100	20 ns	ATA-6
	6^[2]	Ultra ATA/133	133	15 ns	ATA-7
	7	Ultra ATA/167	167	12 ns	CompactFlash 6.0^[3]

References

^ AT Attachment with Packet Interface - 7 Volume 2 - Parallel Transport Protocols and Physical Interconnect (ATA/ATAPI-7 V2) E.2.1.1 Cabling
^ ^a ^b ^c ^d 80-conductor cable required
^ CompactFlash 6.0 Introduction

[1] AT Attachment with Packet Interface - 7 Volume 2 - Parallel Transport Protocols and Physical Interconnect (ATA/ATAPI-7 V2) E.2.1.1 Cabling

[80c-2] 80-conductor cable required

[3] CompactFlash 6.0 Introduction

[1]

[2]

[3]

See also

References