Squeeze the best performance from your ATA disks

Should you use ATA (aka IDE) or SCSI hard disks in your Windows 2000 Professional systems? Whether to use ATA-based disks or their SCSI-based counterparts is one of the industry's oldest debates. In "SCSI and IDE: Defining the Differences," June 1997, I compared the technical underpinnings of the technologies' various flavors and discussed how to use either technology in Windows NT-based systems.

Since I wrote that article, the ATA and SCSI interfaces (not to mention NT) have evolved into newer, more powerful versions. The SCSI realm has expanded to include Ultra2 SCSI, fibre channel, Ultra160 SCSI, and the latest Ultra320 SCSI, providing maximum data transfer rates of 80MBps, 100MBps, 160MBps, and 320MBps, respectively. However, fast performance has always been a SCSI birthright, so perhaps a more significant development is how ATA specifications have bridged the price and performance gaps with their SCSI competitors.

ATA Bridges the Gap
The latest ATA/66 (aka Ultra DMA/66 or UDMA/66) and ATA/100 (aka Ultra DMA/100 or UDMA/100) standards offer fast burst and sustained data transfer rates (66MBps and 100MBps, respectively). The forthcoming SerialATA standard (scheduled to arrive in 2002 at initial speeds of 150MBps and later extend to 300MBps and 600MBps) will stretch ATA's performance boundaries even further. These developments make ATA a viable choice not only for consumer systems and low-end corporate desktops but also for systems that require excellent disk performance.

In real-world environments that use single-disk workstations, the aforementioned maximum data transfer rates aren't typically attainable. System constraints (e.g., ATA chipset limitations, the system bus architecture, physical disk limitations) often prevent such fast data delivery. Nevertheless, largely because of the price premium that SCSI commands (because of higher controller and disk costs), ATA is the primary storage for all but the highest-end desktop workstations. But maximizing the performance of ATA disks under Win2K isn't quite as simple as installing new disk drives and cables.

In an effort to keep up with advancements in ATA storage technology, Microsoft has built some new capabilities into Win2K and has augmented Win2K's ATA support in various service packs and hotfixes. To get ATA devices working properly under Win2K, you need a basic understanding of the ATA interface, required hardware, and related software (e.g., Win2K service packs and hotfixes, built-in and third-party drivers).

Necessary Hardware
First, your system must contain a controller that supports your disks' advanced ATA modes. The most common standards that today's disks support are ATA/33 (aka Ultra DMA/33 or UDMA/33), ATA/66, and ATA/100. Virtually all ATA controllers are backward compatible with disks that use earlier standards. For example, an ATA/100 controller will typically support a disk that supports ATA/33 or even the older IDE or EIDE standards.

On most systems, this controller support is part of the motherboard's ATA chipset. (Intel commands most of the ATA chipset market, but chipset manufacturers such as VIAHardware.com also produce ATA controller chipsets.) However, in some cases, the controller might be an add-on PCI card, such as an ATA RAID controller.

The chipset—the most important component of your ATA system configuration—and its supporting driver control which features are available to disks and other devices attached to the controller. Therefore, an important first task is to thoroughly research the chipset on your motherboard or controller card and determine its capabilities. You can obtain this information from your system, motherboard, or controller-card vendor.

If your ATA chipset is embedded on your system motherboard, you need to verify that your system BIOS supports the ATA modes you intend to use. Although the chipset probably supports a particular ATA mode, the system's BIOS revision (which the system or chipset manufacturer typically updates regularly) might not support that mode. In such a case, you should be able to obtain a BIOS update from your system or motherboard manufacturer's support Web site.

Next, you need to ensure that your hardware offers the proper ATA support and is properly configured for optimal performance. First, make sure that all involved hard disks support the desired ATA modes of operation (e.g., ATA/66, ATA/100). Second, isolate the disks onto separate channels. This isolation is important because an ATA channel defaults to the speed of the slowest disk on the channel. If ATA/33- and ATA/100-capable disks reside on the same channel, the maximum attainable speed will be that of ATA/33. Therefore, place your slow ATA devices (e.g., CD-ROM, CD-R, CD-RW, Zip, older hard disks) on one channel and your fast ATA hard disks on another channel.

You also need to ensure that you're using the correct cables. The ATA/33, ATA/66, and ATA/100 specifications require the use of special 80-conductor ribbon cables, as opposed to the 40-conductor cables that earlier ATA disks use. The additional conductors function as grounding paths that improve the cable's signal-to-noise ratio. Finally, drive-placement requirements for the 80-conductor cables are different from earlier cables' requirements. You must place the master device (Drive 0) at the end of an 80-conductor cable, and you must place the slave device (Drive 1) at the middle connector. The blue connector at one end is for the host system or controller card, the gray connector in the middle is for the slave device, and the black connector at the other end is for the master device.

In my next column, I'll discuss your next step—software—and Win2K's built-in ATA drivers and third-party drivers. In the meantime, if you'd like to explore the details of today's various ATA and SCSI specifications, check out "Web Resources".


WEB RESOURCES
SCSI specifications
Gary Field's SCSI Info Central
http://www.scsifaq.org
SCSI Trade Association
http://www.scsita.org
Ultra160 SCSI
http://www.ultra160-scsi.com
ATA specifications
AnandTech
http://www.anandtech.com/guides/viewfaq.html?i=53
Intel
http://support.intel.com/support/chipsets/
storagedrivers/ultraata
Seagate Technology
http://www.seagate.com/support/kb/disc/ultra_
ata_faq.html
SerialATA's FAQ
http://www.serialata.com
Cabling
Micro Firmware
http://www.firmware.com/support/bios/udmacabl.htm
ConnectWorld
http://www.connectworld.net/c6.html