The Free On-line Dictionary of Computing (30 December 2018):

ATA-4
UDMA
Ultra-ATA
Ultra DMA

    (Or "Ultra DMA", "UDMA", "Ultra-ATA", "Ultra-DMA/33") A
   development of the Advanced Technology Attachment specifications
   which gives nearly twice the maximum transfer rate of the ATA-3
   standard (PIO Mode 4).

   ATA-4 Extensions Ultra DMA/33 Synchronous DMA Mode maximum burst
   transfer rates:

   	Mode 	Cycle Time 	Transfer Rate
   		ns		MB/s
   	0 	235 		16
   	1 	160 		24
   	2 	120 		33

   This is achieved by improving timing windows in the protocol
   on the ATA interface; reducing propagation delays by
   pipelining data transfers and transferring data in
   synchronous (strobed) mode.

   Developed by Quantum Corporation, ATA-4 has been freely
   licensed to manufacturers and is supported by Intel
   Corporation.

   (1998-09-30)