First published in 1998, ATA-4 included several important additions to the standard. It included the Packet Command feature known as the AT Attachment Packet Interface (ATAPI), which allowed devices such as CD-ROM and CD-RW drives, LS-120 SuperDisk floppy drives, Zip drives, tape drives, and other types of storage devices to be attached through a common interface.

Until ATA-4 came out, ATAPI was a separately published standard. ATA-4 also added the 33MB per second (MBps) transfer mode known as Ultra-DMA or Ultra-ATA. ATA-4 is backward-compatible with ATA-3 and earlier definitions of the ATAPI. The major revisions added in ATA-4 were as follows:

• Ultra-DMA (UDMA) transfer modes up to Mode 2, which is 33MBps (called UDMA/33 or Ultra-ATA/33)

• Integral ATAPI support

• Advanced power management support

• Defined an optional 80-conductor, 40-pin cable for improved noise resistance

• Compact Flash Adapter (CFA) support

• Introduced enhanced BIOS support for drives over 9.4ZB (zettabytes or trillion gigabytes) in size (even though ATA was still limited to 136.9GB)

ATA-4 was published as ANSI NCITS 317-1998, ATA-4 with Packet Interface Extension. The speed and level of ATA support in your system is mainly dictated by your motherboard chipset.

Most motherboard chipsets come with a component called either a South Bridge or an I/O Controller Hub that provides the ATA interface (as well as other functions) in the system. Check the specifications for your motherboard or chipset to see whether yours supports the faster ATA/33, ATA/66, ATA/100, or ATA/133 mode.

One indication is to enter the BIOS Setup, put the hard disk on manual parameter settings (user defined), and see which (if any) Ultra-DMA modes are listed. Most boards built during 1998 support ATA/33; in 2000 they began to support ATA/66; and by late 2000 most started supporting ATA/100. ATA/133 support became widespread in mid-2002.

ATA-4 made ATAPI support a full part of the ATA standard, and thus ATAPI was no longer an auxiliary interface to ATA but merged completely within it. Thus, ATA-4 promoted ATA for use as an interface for many other types of devices. ATA-4 also added support for new Ultra-DMA modes (also called Ultra-ATA) for even faster data transfer.

The highest-performance mode, called UDMA/33, had 33MBps bandwidth—twice that of the fastest programmed I/O mode or DMA mode previously supported. In addition to the higher transfer rate, because UDMA modes relieve the load on the processor, further performance gains were realized.

An optional 80-conductor cable (with cable select) is defined for UDMA/33 transfers. Although this cable was originally defined as optional, it would later be required for the faster ATA/66, ATA/100, and ATA/133 modes in ATA-5 and later. Many hard drives purchased in retail kits include the 80-wire cable, although other types of devices, such as optical drives, include only a 40-wire cable.

Also included was support for queuing commands, which is similar to that provided in SCSI-2. This enabled better multitasking as multiple programs make requests for ATA transfers.

Another standard approved by the T13 committee in 1998 is "ANSI NCITS 316-1998 1394 to AT Attachment - Tailgate," which is a bridge protocol between the IEEE-1394 (iLink/FireWire) bus and ATA that enables ATA drives to be adapted to FireWire.

A tailgate is an adapter device (basically a small circuit board) that converts IEEE-1394 (iLink or FireWire) to ATA, essentially allowing ATA drives to be plugged into a FireWire bus.

This has enabled vendors such as Maxtor, Western Digital, and others to quickly develop IEEE-1394 (FireWire) external drives for backup and high-capacity removable data storage. Inside almost any external FireWire drive enclosure you will find the tailgate device and a standard ATA drive.