IDE Variations


There have been four main types of IDE interfaces, based on three bus standards:

  • SATA

  • PATA (based on the 16-bit AT-bus, also called ISA)

  • XT IDE (based on 8-bit ISA, obsolete)

  • MCA IDE (based on 16-bit Micro Channel, obsolete)

Of these, only the PATA and SATA versions are used today. PATA and SATA have evolved with newer, faster, and more powerful versions. The newer versions of PATA are referred to as ATA-2 and higher. They are also sometimes called EIDE (Enhanced IDE), Fast ATA, Ultra ATA, or Ultra DMA (UDMA). Even though PATA has hit the end of the evolutionary road with ATA-7, SATA picks up where PATA leaves off and offers greater performance, higher reliability, easier installation, lower cost, and an established roadmap for future upgrades.

Note

It is important to note that only the ATA IDE interface has been standardized by the industry. The XT and MCA IDE interfaces were never adopted as industrywide standards and never became very popular. These interfaces were only used from 1987 to 1993 and only in IBM PS/2 (and some early ThinkPad) systems.


In most modern server systems, you find one or more PATA connectors on the motherboard, and systems that offer ATA RAID have two additional PATA connectors, which can be used for an ATA RAID array or for additional ATA drives running as independent devices. If your motherboard does not have one of these connectors and you want to attach an ATA drive to your system, you can purchase an adapter card that adds an ATA interface (or two) to a system via the PCI or PCI-X bus slots. Some of the cards offer additional features, such as an onboard ROM BIOS or cache memory.

Because only the PATA and SATA versions of IDE are in use today, this chapter focuses on them.

Note

Many people who use systems with ATA connectors on the motherboard believe that a hard disk controller is built in to their motherboard, but in a technical sense, the controller is actually in the drive. Although the integrated ATA ports on a motherboard are often referred to as controllers, they are more accurately called host adapters (although you rarely hear this term). A host adapter can be thought of as a device that connects a controller to a bus.


PATA is a 16-bit parallel interface, meaning that 16 bits are transmitted simultaneously down the interface cable. A serial interface called SATA was officially introduced in late 2000 and began appearing in systems starting in 2003. SATA sends 1 bit down the cable at a time, enabling thinner and smaller cables to be used and providing higher performance due to the higher cycling speeds allowed. SATA is a completely new and updated physical interface design, while remaining compatible on the software level with PATA. (Throughout this book, ATA refers to both the parallel and serial versions, whereas PATA and SATA refer to the specific versions, as indicated.) Figure 6.1 shows how the power and data cables used by SATA compare in size to those used by PATA.

Figure 6.1. SATA data cables (lower right) are much smaller than those used by PATA (upper right), whereas the power cables (left) are similar in size.


The primary advantage of ATA drives over the older, separate controller-based interfaces and newer host bus interface alternatives, such as USB, SCSI, and IEEE 1394 (i.LINK or FireWire), is cost. Because the separate controller or host adapter is eliminated and the cable connections are simplified, ATA drives cost much less than a standard controller-and-drive combination.

See "ANSI SCSI Standards," p. 449.

See "USB," p. 468.


In terms of performance, ATA drives are often some of the highest-performance drives available, but they can also be among the lowest-performance drives. This apparent contradiction is a result of the fact that all ATA drives are different. You can't make a blanket statement about the performance of ATA drives because each drive is unique. The high-end models, however, offer performance equal to or superior to that of any other type of drive on the market for a single-user, single-tasking operating system. However, because of the simplicity of the ATA design, PATA in particular is not suitable for midrange or high-end server designs. PATA is adequate for entry server designs, though.

Note

Many people are confused about 16- versus 32-bit bus connections and 16- versus 32-bit hard drive connections. A PCI bus connection allows for a 32-bit (and possibly 64-bit, in some versions) connection between the bus and the ATA host interface, which is typically in the motherboard chipset South Bridge or I/O Controller Hub (ICH) chip. However, the actual PATA interface between the host connector on the motherboard and the drive (or drives) itself is only a 16-bit interface. Thus, in a PATA drive configuration, you are still getting only 16-bit transfers between the drive and the motherboard-based host interface. Even so, the clock speeds of the ATA interface are high enough that one or two hard drives normally can't supply the controller enough data to saturate even a 16-bit channel. The same is true with SATA, whichalthough it transmits only 1 bit at a timedoes so at extremely high speeds.





Upgrading and Repairing Servers
Upgrading and Repairing Servers
ISBN: 078972815X
EAN: 2147483647
Year: 2006
Pages: 240

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