Source : Free On-Line Dictionary of Computing

ATA-4
     
         /ul'tr* D M A/ (Or "Ultra DMA", "UDMA", "Ultra-ATA",
        "Ultra-DMA/33") A development of the {Advanced Technology
        Attachment} specifications which gives nearly twice the
        maximum transfer speed 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)