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Practical Application

ATA-7

ATA-7 brought two new innovations to the ATA world: one evolutionary and the other revolutionary. The evolutionary innovation came with the last of the parallel ATA Ultra DMA modes; the revolutionary was a new form of ATA called serial ATA (SATA).

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EXAM TIP You need to know this whole chapter for the Essentials exam, so don’t skip the rest just because of the “Practical Application” heading.

ATA/133

ATA-7 introduced the fastest and probably least adopted of all of the ATA speeds, Ultra DMA mode 6 (ATA/133). Even though it runs at a speed of 133 MBps, the fact that it came out with SATA kept many hard drive manufacturers away. ATA/133 uses the same cables as Ultra DMA 66 and 100.

While you won’t find many ATA/133 hard drives, you will find plenty of ATA/133 controllers. There’s a trend in the industry to color the controller connections on the hard drive red, although this is not part of the ATA-7 standard.

Serial ATA

The real story of ATA-7 is SATA. For all its longevity as the mass storage interface of choice for the PC, parallel ATA has problems. First, the flat ribbon cables impede airflow and can be a pain to insert properly. Second, the cables have a limited length, only 18 inches. Third, you can’t hot-swap PATA drives. You have to shut down completely before installing or replacing a drive. Finally, the technology has simply reached the limits of what it can do in terms of throughput.

Serial ATA addresses these issues. SATA creates a point-to-point connection between the SATA device—hard disk, CD-ROM, CD-RW, DVD-ROM, DVD-RW, BD-R, BD-RE, and so on—and the SATA controller, the host bus adapter (HBA). At a glance, SATA devices look identical to standard PATA devices. Take a closer look at the cable and power connectors, however, and you’ll see significant differences (Figure 11-19).

Figure 11-19 SATA hard disk power (left) and data (right) cables

Because SATA devices send data serially instead of in parallel, the SATA interface needs far fewer physical wires—seven instead of the eighty wires that is typical of PATA—resulting in much thinner cabling. This might not seem significant, but the benefit is that thinner cabling means better cable control and better airflow through the PC case, resulting in better cooling.

Further, the maximum SATA-device cable length is more than twice that of an IDE cable—about 40 inches (1 meter) instead of 18 inches. Again, this might not seem like a big deal unless you’ve struggled to connect a PATA hard disk installed into the top bay of a full-tower case to an IDE connector located all the way at the bottom of the motherboard.

SATA does away with the entire master/slave concept. Each drive connects to one port, so no more daisy-chaining drives. Further, there’s no maximum number of drives—many motherboards are now available that support up to eight SATA drives. Want more? Snap in a SATA HBA and load ’em up!

The big news, however, is in data throughput. As the name implies, SATA devices transfer data in serial bursts instead of parallel, as PATA devices do. Typically, you might not think of serial devices as being faster than parallel, but in this case, that’s exactly the case. A SATA device’s single stream of data moves much faster than the multiple streams of data coming from a parallel IDE device—theoretically up to 30 times faster. SATA drives come in two common varieties, the 1.5Gb and the 3Gb, that have a maximum throughput of 150 MBps and 300 MBps, respectively.

Number-savvy readers might have noticed a discrepancy between the names and throughput of the two SATA drives. After all, 1.5 Gb per second throughput translates to 192 MB per second, a lot higher than the advertised speed of a “mere” 150 MBps. The same is true of the 3Gb/300 MBps drives. The encoding scheme used on SATA drives takes about 20 percent of the overhead for the drive, leaving 80 percent for pure bandwidth. The 3 Gb drive created all kinds of problems,