6.1. ATAIDE Hard Drive Technology

6.1. ATA/IDE Hard Drive Technology

ATA was developed as a device attachment interface for the original IBM AT computer. HP, CDC, and Western Digital developed the original ATA interface and disk drives in the 1980s. In the late 1980s, the ATA interface design was set as an American National Standards Institute (ANSI) standard.

The ATA interface is the drive controller interface and the standard that defines the drive and how it operates. IDE is the actual drive and the 40-pin interface and drive controller architecture designed to implement the ATA standard.

6.1.1 ATA/IDE in Servers

Traditionally, ATA/IDE hard drives have been used in desktops and portable computers, but they have not been common in servers. However, low-cost ATA/IDE hard drives are an emerging opportunity for specific environments in which server duty cycle is relatively low and low price is the motivating force.

ATA/IDE hard drive technology offers several basic advantages, including the following:

• Lowest dollar per gigabyte

• Lowest power consumption

• Lower thermals

• Entry-level reliability

ATA/IDE is also known as parallel ATA. Because of the recent development of the serial ATA standard, parallel ATA is the now preferred term because it distinguishes between the two standards.

6.1.2 ATA/IDE Standards

Each version of ATA is backward compatible with the previous versions. Newer versions of ATA are built on older versions. With just a few exceptions, new versions can be thought of as extensions of the previous versions.

The ATA standards are described in Table 6.1.

Table 6.1. ATA Standards

Standard	Description
ATA-1	Defines the original ATA interface, which is an integrated bus interface between disk drives and host systems based on the ISA bus.
ATA-2	Includes performance-enhancing features such as programmed input/output (PIO) and direct memory access (DMA) modes. EIDE is an extension of ATA-2 and builds on both the ATA-2 and ATA Packet Interface (ATAPI) standards.
ATA-3	Improves the reliability of PIO mode 4; offers a simple password-based security scheme, more sophisticated power management features, and Self-Monitoring Analysis and Reporting Technology (S.M.A.R.T.). ATA-3 is backward compatible with ATA-2, ATAPI, and ATA-1 devices.
ATA-4 (Ultra-ATA/33)	Provides high-performance bus mastering at burst data rates up to 33MB/s using DMA data transfers. The implementation of Ultra-ATA is usually called Ultra-DMA/33 or UDMA/33. Implementing an Ultra-ATA drive system requires an Ultra-ATA drive, controller, and supporting BIOS.
ATA-5 (Ultra-ATA/66)	Supports high-performance bus mastering with burst data rates up to 66MB/s using DMA data transfers. This implementation of Ultra-ATA is usually called Ultra-DMA/66 or UDMA/66. An Ultra-ATA/66 drive requires a controller, cable, and supporting BIOS.
	The signal cable is a specially designed 40-pin/80-conductor cable for Ultra-ATA/66 or Ultra-ATA/100. It is fully backward compatible with previous ATA standards, but will not provide the UDMA performance with a standard 40-pin cable. The operating system must be DMA-capable, and the DMA mode must be activated.
ATA-6 (Ultra-ATA/100)	Provides backward compatibility with existing EIDE/UDMA hard drives, removable media drives, and CD-ROM and R/RW drives. Ultra-ATA/100 drives, also called Ultra-DMA/100 or UDMA/100, are capable of 100MB/s data burst rates, which is a design modification originally created by Intel, Quantum, and Seagate.
	A sensing mechanism allows the host to detect the 80-conductor cable and determine whether to enable Ultra ATA/66/100 transfer rates. Ultra ATA/100 requires the same 80-conductor cable as Ultra ATA/66. The Ultra ATA/33 requires a 40-conductor cable.
ATA-7 (Ultra-ATA/133)	Raises the ATA interface speed to 133MB/s and aligns the interface rate with the PCI bus data rate. Introduced by Maxtor, it was built on the double-edge clocking technology and cyclical redundancy checking of Ultra ATA/33 and the 80-conductor cable introduced with the Ultra ATA/66 interface. Backward compatible with all parallel ATA devices, it uses the same 80-conductor, 40-pin cable currently deployed for ATA/100.

6.1.3 ATAPI

ATA Packet Interface (ATAPI) is an extension of the ATA interface, designed to allow devices other than hard drives to plug into an ordinary ATA/IDE port.

ATAPI is a standard, packet-based interface that derives its command set from SCSI. It provides the commands needed for devices such as CD-ROMs and tape drives that plug into an ordinary ATA/IDE connector. ATAPI also runs other removable storage devices, such as the LS-120 super-disk drives and internal Iomega Zip and Jaz drives.

The ATAPI specification was first defined under ATA-2, which is now obsolete. The current version of ATAPI was defined as part of ATA-4 specification.

6.1.4 Emerging Technologies Serial ATA

Serial ATA technology enables the industry to move to the lower voltages and lower pin count required for efficient integration in future chipsets. Serial ATA is a point-to-point interface in which each device is directly connected to the host, using a dedicated link. As with parallel ATA, Serial ATA was designed only as an internal storage interface.

Serial ATA offers improvements and capabilities over parallel ATA, including the following:

• No drive jumpers Eliminates the primary/secondary interaction between devices. Each device has the entire interface bandwidth dedicated to it.

• Lower voltage Serial ATA reduces the signaling voltages from 5V to approximately 250 millivolts.

• Pin efficiency The ATA interface has 26 signal pins going into the interface chip. Serial ATA uses only 4 signal pins, improving the pin efficiency.

• Improved cable and connector The serial ATA cable length is 1 meter, which is considerably longer than the 18-inch maximum for parallel ATA. The current parallel ATA cable and connector is an 80-conductor ribbon cable and 40-pin header connector. Serial ATA uses much thinner cables with only 7 pins and smaller redesigned cable connectors.

• Hot-plug capability Serial ATA includes all the mechanical and electrical features necessary to allow devices to be inserted directly into receptacles when the system is powered, and the protocol ensures that device discovery and initialization are handled.

• Compatibility Serial ATA is compatible at the register level with the current parallel ATA. Serial ATA supports all existing ATA and ATAPI devices.

• Scalability The current parallel ATA interface does not have scalability to support several more speed doublings. Serial ATA defines a road map starting at 1.5Gb/s and migrating to 3Gb/s, then to 6Gb/s.

• Reliability Serial ATA uses a special encoding scheme called 8B/10B to encode and decode data sent along the cable. This guarantees steady streamed voltage signal pulses on the circuits to increase reliability.

6.1.4.1 SERIAL ATA II

In the first quarter of 2002, the formation of the Serial ATA II Working Group was announced. The group's charge is to develop a Serial ATA II specification that will enhance the existing Serial ATA specification for the server and networked storage market segments, as well as deliver second-generation signaling speed.