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SSDs that use SDRAM cache are volatile and lose data when powered off. Others that use nonvolatile flash memory such as NAND retain data when power is turned off or disconnected. (See Chapter 13, “Removable Media,” for the scoop on flash memory technology.)

SSDs are more expensive than traditional HDDs. Less expensive SSDs typically implement less reliable multi-level cell (MLC) memory technology in place of the more efficient single-level cell (SLC) technology to cut costs.

Parallel and Serial ATA

Over the years, many interfaces existed for hard drives, with such names as ST-506 and ESDI. Don’t worry about what these abbreviations stood for; neither the CompTIA A+ certification exams nor the computer world at large has an interest in these prehistoric interfaces. Starting around 1990, an interface called advanced technology attachment (ATA) appeared that now virtually monopolizes the hard drive market. ATA hard drives are often referred to as integrated drive electronics (IDE) drives. Only one other type of interface, the moderately popular small computer system interface (SCSI), has any relevance for hard drives.

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NOTE The term IDE (integrated drive electronics) refers to any hard drive with a built-in controller. All hard drives are technically IDE drives, although we only use the term IDE when discussing ATA drives.

ATA drives come in two basic flavors. The older parallel ATA (PATA) drives send data in parallel, on a 40- or 80-wire data cable. PATA drives dominated the industry for more than a decade, but have been mostly replaced by serial ATA (SATA) drives that send data in serial, using only one wire for data transfers. The leap from PATA to SATA is only one of a large number of changes that have taken place with ATA. To appreciate these changes, we’ll run through the many ATA standards forwarded over the years.

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NOTE Modern external drives connect to a FireWire, Hi-Speed USB 2.0, or eSATA port. All three interfaces offer high data transfer rates and hot-swap capability, making them ideal for transporting huge files such as digital video clips. Regardless of the external interface, however, inside the casing you’ll find an ordinary PATA or SATA drive, just like those described in this chapter.

ATA-1

When IBM unveiled the 80286-powered IBM PC AT in the early 1980s, it introduced the first PC to include BIOS support for hard drives. This BIOS supported up to two physical drives, and each drive could be up to 504 MB—far larger than the 5-MB and 10-MB drives of the time. Although having built-in support for hard drives certainly improved the power of the PC, installing, configuring, and troubleshooting hard drives could at best be called difficult at that time.

To address these problems, Western Digital and Compaq developed a new hard drive interface and placed this specification before the American National Standards Institute (ANSI) committees, which in turn put out the AT Attachment (ATA) interface in March of 1989. The ATA interface specified a cable and a built-in controller on the drive itself. Most importantly, the ATA standard used the existing AT BIOS on a PC, which meant that you didn’t have to replace the old system BIOS to make the drive work—a very important consideration for compatibility, but one that would later haunt ATA drives. The official name for the standard, ATA, never made it into the common vernacular until recently, and then only as PATA to distinguish it from SATA drives.

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NOTE The ANSI subcommittee directly responsible for the ATA standard is called Technical Committee T13. If you want to know what’s happening with ATA, check out the T13 Web site: www.t13.org.

Early ATA Physical Connections

The first ATA drives connected to the computer with a 40-pin ribbon cable that plugged into the drive and into a hard drive controller. The cable has a colored stripe down one side that denotes pin 1 and should connect to the drive’s pin 1 and to the controller’s pin 1. Figure 11-7 shows the business end of an early