Introduction
Since its introduction into PC motherboards and add-on controllers in 1999 (or 2000, for Apple computers), computer buyers have seen a growing number of references to UDMA/66 (UDMA stands for "Ultra Direct Memory Access"), a faster interface for your computer's hard drive than the UDMA/33 specification that was the norm in 1998 and is still the standard in some of today's motherboards and hard drives. Already, manufacturers are rolling out new lines of ATA (AT Attachment) drives exploiting this new interface.
UDMA is a currently popular hard drive specification that provides up to 33.3 MB/sec transfer rates from inexpensive mass storage devices connected to a computer's EIDE (Enhanced Integrated Drive Electronics) bus. UDMA requires a supported motherboard (or UDMA controller card add-on), a UDMA-compatible drive, and a supported operating system (e.g., Windows 98). An updated version of the specification, known as UDMA/66, provides performance comparable to much more expensive Ultra Wide SCSI 2 drives, with up to 66.6 MB/sec transfer rates. The current BX chipset does not support UDMA/66. A new generation of motherboards (or add-on UDMA/66 controller cards), using a forthcoming Intel chipset currently code-named "Camino," will be required to support UDMA/66 when the 133MHz bus versions of Pentium III and UDMA/66 devices become available in mid-1999.
IDE, or Integrated Drive Electronics is the method by which most hard drives, internal CD-ROM drives, and other internal storage devices are connected to a computer. Today’s better hard drives are referred to as UDMA or Ultra ATA (two ways of saying the same thing), but they are still IDE-based. Some high-performance systems use SCSI drives instead of those connected via IDE. See also: EIDE, UDMA.
UltraATA or UltraDMA?
Generally, the term UltraDMA refers to the motherboard, bus or add-in controller; UltraATA or UltraIDE is commonly used in reference to the drives. In other words, an UltraATA drive connects to an UltraDMA controller. See the glossary for more details.
Speed
As noted above, performance of the UltraDMA/66 bus is comparable to much more expensive Ultra Wide SCSI 2, which delivers up to 80MB/sec. Notably, drives based on the much ballyhooed "FireWire" IEEE 1394 spec deliver a maximum throughput of only 50MB/sec. In all cases, the words "up to" should be noted. ATA/66 drives may deliver up to 66MB/sec transfer rates, but these are "burst" data transfer rates; the average number of megabytes per second transferred will be much lower, due to limitations of the operating system, file fragmentation, bus contention, and other issues. Also, just because a drive employs UltraDMA doesn't mean it is a fast mechanism to start with. Quantum's new CR Ultra ATA-66 13.3 GB hard drive, for example, is a 5400RPM drive only slightly faster than the company's older Ultra ATA/33 EX drive -- and both are slower than a good UltraATA/33 drive such as Maxtor's now-aging DiamondMax 4320.
Cost compared to SCSI
The big advantage, of course, of UltraATA drives is their relatively low cost. Seagate, for example, has announced the U4, which it says is the first Ultra ATA/66 drive in the entry-level market, and Seagate's second generation of disc drives designed specifically for the growing sub-$1,000 PC market. For details, see the Press Release.
How to add it
There are several PCI add-on UDMA controllers available on the market, from Promise Technologies, Abit, Iwill and others. There units will add support for the latest drives to existing UDMA/33 and other IDE/33 systems. Promise was first to market with its PCI controller, the Ultra66.
Abit's product, dubbed Hot Rod66 offers support for four devices, and is claimed to automatically detect any combination of UDMA/66,UDMA/33,EIDE,or ATAPI devices. At this time, we think it is the top product in the category.
Iwill's SIDE Pro66 controller provides two IDE hard drive connectors that support Ultra ATA/66. Each IDE connector supports a master/slave combination of any IDE device, including IDE, EIDE and Ultra-ATA standards.
Caveats
There are some things to watch out for if you are to have success. You must not mix ATA/66 and non Ultra DMA devices on the same IDE "chain" and there are some operating system compatibility issues and other possible caveats. See the page at http://www.arstechnica.com/reviews/3q99/bp6/bp6-2.html for a list of conditions that must be true for ATA/66 to work as expected.
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