Technical The Internal Components E-IDE Interface

Enhanced - Integrated Drive Electronics

The Ultra DMA/ interface also known as Ultra ATA/ is a low cost upgrade to previous DMA interfaces that increases the data transfer rate. (See table at the end of the page). Hard drive transfer rates have been doubling every few years.

In 1994, DMA Mode 2 was introduced and could attain a possible transfer rate of about 16 Mb per second (That's bits not bytes), then at the end of 1997, Ultra DMA/33 was introduced offering 33.3 Mbs. In 1999 it doubled yet again to Ultra DMA/66 and offered 66.6 Mbs data transfer from the hard disk to the hard disk controller. When this document was written (Sept 2001), Ultra DMA/100 drives have already appeared. It now looks however, like the parallel bus architecture used by IDE devices has reached its limit. There is possibly going to be a new serial bus design that will overcome many of the limitations that plague current parallel bus drive technology, such as error checking and higher necessary voltages.

Ultra DMA/66 also improved data integrity through the use of a new a style 40 pin 80 cable connector and Cyclic Redundancy Checks (CRC's). Each cable is now also shielded by its own ground cable although there are still only 40 pins this reduces cross-talk and improves signal integrity. The Ultra DMA/66 cable connector is backward compatible with existing Ultra DMA and DMA devices such as EIDE/IDE hard disks and CD-ROM's and host systems.

The transfer of large files, often written sequentially on the hard drive is affected by the transfer rate. During sequential reads the hard drive may fill up its internal buffer faster than the host can empty it when using Ultra DMA/33 or older Multi-DMA interfaces. Improving the interface to keep up with the the internal transfer rate is accomplished with Ultra DMA/66 and Ultra DMA/100, although the real actual gains probably will go unnoticed and probably only be seen during long sequential transfers such as replaying a movie.

To use Ultra DMA/33, 66 or 100 the PC system must have the equivalent Ultra DMA logic either on the motherboard or on a PCI expansion card. The PC must also have a equivalent Ultra DMA BIOS and a Ultra DMA aware device driver for the operating system and to use Ultra DMA/66 or 100 the system needs a 40 pin 80 cable connector. Windows itself, doesn't need to be configured to use higher Ultra DMA/33 and above as long as it is already set to use DMA mode transfers.

SCSI Interface