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Figure 11-7 Back of IDE drive showing 40-pin connector (left), jumpers (center), and power connector (right)

The controller is the support circuitry that acts as the intermediary between the hard drive and the external data bus. Electronically, the setup looks like Figure 11-8.

Figure 11-8 Relation of drive, controller, and bus

Wait a minute! If ATA drives are IDE, they already have a built-in controller. Why do they then have to plug into a controller on the motherboard? Well, this is a great example of a term that’s not used properly, but everyone (including the motherboard and hard drive makers) uses it this way. What we call the ATA controller is really no more than an interface providing a connection to the rest of the PC system. When your BIOS talks to the hard drive, it actually talks to the onboard circuitry on the drive, not the connection on the motherboard. But, even though the real controller resides on the hard drive, the 40-pin connection on the motherboard is called the controller. We have a lot of misnomers to live with in the ATA world.

The ATA-1 standard defined that no more than two drives attach to a single IDE connector on a single ribbon cable. Because up to two drives can attach to one connector via a single cable, you need to be able to identify each drive on the cable. The ATA standard identifies the two drives as “master” and “slave.” You set one drive as master and one as slave by using tiny jumpers on the drives (Figure 11-9).

Figure 11-9 A typical hard drive with directions (top) for setting a jumper (bottom)

The controllers are on the motherboard and manifest themselves as two 40-pin male ports, as shown in Figure 11-10.

Figure 11-10 IDE interfaces on a motherboard

PIO and DMA Modes

If you’re making a hard drive standard, you must define both the method and the speed at which the data’s going to move. ATA-1 defined two methods, the first using programmed I/O (PIO) addressing and the second using direct memory access (DMA) mode.

PIO is nothing more than the traditional I/O addressing scheme, where the CPU talks directly to the hard drive via the BIOS to send and receive data. Three different PIO speeds called PIO modes were initially adopted:

PIO mode 0: 3.3 MBps (megabytes per second)

PIO mode 1: 5.2 MBps

PIO mode 2: 8.3 MBps

DMA modes defined a method to enable the hard drives to talk to RAM directly, using old-style DMA commands. (The ATA folks called this single-word DMA.) This old-style DMA was slow, and the resulting three ATA single-word DMA modes were also slow:

Single-word DMA mode 0: 2.1 MBps

Single-word DMA mode 1: 4.2 MBps

Single-word DMA mode 2: 8.3 MBps

When a computer booted up, the BIOS queried the hard drive to see what modes it could use and then automatically adjusted to the fastest mode.

ATA-2

In 1990, the industry adopted a series of improvements to the ATA standard called ATA-2. Many people called these new features Enhanced IDE (EIDE). EIDE was really no more than a marketing term invented by Western Digital, but it caught on in common vernacular and is still used today, although its use is fading. Regular IDE drives quickly disappeared, and by 1995, EIDE drives dominated the PC world. Figure 11-11 shows a typical EIDE drive.

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Figure 11-11 EIDE drive

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NOTE The terms ATA, IDE, and EIDE are used interchangeably.

ATA-2 was the most important ATA standard, as it included powerful new features such as higher capacities, support for non–hard drive storage devices, support for two more ATA devices for a maximum of four, and substantially improved throughput.

Higher Capacity with LBA

IBM created the AT BIOS to support hard drives many years before IDE drives were invented, and every system had that BIOS. The developers of IDE made certain that the new drives would run from the same AT BIOS command set. With this capability, you could use the same CMOS and BIOS routines to talk to a much more advanced drive. Your