(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.