Hardware & Infrastructure
Commentary
3/9/2006
02:43 PM
Fred Langa
Fred Langa
Commentary
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Langa Letter: How To Safely Add Or Replace A Hard Drive

Want to expand your PC without having to rebuild your operating system? Fred Langa shows you how to do that--and more.

Live-Swapping Or Upgrading A Drive
We'll spend most of our time in this column discussing live-swapping or upgrading a drive because it's more complex than simply adding a second drive to a system and thus deserves more attention. Although we'll come back to the simpler case of adding a second drive, by discussing the more complex process in some detail first, we'll automatically cover essential information that will also apply to the simpler procedure later.

Similarly, we'll focus on tasks involving classic IDE (integrated drive electronics)-type drives and cables using standard ATA connections. ATA stands for "Advanced Technology Attachment," where "Advanced Technology" in turn refers to the IBM AT PC, introduced in 1984. Believe it or not, and despite its age, ATA is still the most common kind of drive attachment technology in use today.

The concepts and principles are very similar for newer SATA drives, but the cables and connectors are different. (SATA means "Serial ATA" or "Serial Advanced Technology Attachment." For lots more information, see this.)

Some other basics: Most PCs have two "channels" for drive communication: a primary and a secondary. Furthermore, in a standard PC setup, each channel can support two drives. Historically, they've been called the "master" and "slave," so a PC with four drives would have a primary master, a primary slave, a secondary master, and a secondary slave.

I wish I were making this up, but some vendors have been accused of cultural insensitivity in the use of this nomenclature and so have started calling the drives "primary" and "secondary" as well, leading to situations where you may have a primary primary, a primary secondary, a secondary primary, and a secondary secondary. While I applaud linguistic sensitivity, this naming convention is just plain silly and confusing, so we'll use the simpler, clearer "master" and "slave" terminology just for what it is, with no deeper context implied and no offense intended to anyone.

A PC knows which drive is which by three means. First, the primary and secondary channels are separate. Each has its own cable and plugs into the motherboard via a separate socket.

Incidentally (but importantly), each drive channel may end up working at the speed of the slowest device on that channel. Thus it's usually better to group like devices together. For example, CD/DVDs are much slower than hard drives, so in a system with a mix of hard drives and CD/DVD drives, it makes sense to put the hard drive(s) on one channel and the CD drive(s) on the other. This is actually one of the reasons why PCs have separate channels in the first place--so devices with very different speeds can be grouped where they won't get in each other's way.

Better-quality cables are clearly marked, but almost all current cables are color-coded and keyed so that it's nearly impossible to plug things together the wrong way.

(click image for larger view)
Photo One
Better-quality cables are clearly marked, but almost all current cables are color-coded and keyed so that it's nearly impossible to plug things together the wrong way.
By convention, each drive cable has three connectors: one for the motherboard, and two for the drives. The two drive connectors are usually fairly close together on one end of the cable, so even if the cable has no labeling whatsoever, you can still tell which end is which. (The connector on one end of the cable that's more or less by itself is the one that plugs into the motherboard. The other two connectors, more or less together on the other end of the cable, are for the drives.)

Also by convention, the connector at the end of the cable farthest from the motherboard is for the master drive. The other connector, near the master drive's end of the cable, is for the slave drive. In systems with only one hard drive, only the master connection is used; the slave connector can be left unattached to anything.

In better-quality systems, the connections are also color-coded to make the setup even more obvious. As shown in Photo One, the blue connector plugs into the motherboard, the black connector (on the other end of the cable) plugs into the master drive, and the gray connector (midway in the cable) plugs into the slave drive. What's more, some cables even print text labels on or near the connectors, making the connection order just about foolproof. This, too, is shown in Photo One.

In newer PCs, the connectors themselves also are "keyed," meaning they're shaped so that they only fit into sockets the right way. If you try to plug a connector in the wrong way, it just won't fit.


Photo Two
The plastic ridges and slots on the plug take the worry out of connections. If you try to plug a connector in the wrong way, it just won't fit.

(click image for larger view)

The plastic ridges and slots on the plug take the worry out of connections. If you try to plug a connector in the wrong way, it just won't fit.

Although this is increasingly rare, in some older systems (older cables and/or older drives) there's no physical keying to prevent plugging things in the wrong way. These systems rely on color-coding of the cable itself for proper orientation. One side of the cable is printed with a red stripe as shown in Photo Three.


Even on older cables, the red stripe makes it easy to get things plugged in correctly. See the text for details.
Photo Three
Even on older cables, the red stripe makes it easy to get things plugged in correctly. See the text for details.

(click image for larger view)

This red stripe aligns with the side of the drive connector labeled "Pin 1," usually printed or embossed on the drive itself. But again note that this is a fall-back option; most current drives and cables use keyed connectors that can only plug in the correct way. The red-stripe/Pin 1 orientation method is only needed in cases where the drives or connectors aren't keyed.

Like many cables of current manufacture, our example cable (shown in all three photos above) actually uses all these conventions together--physical layout, color coding, text labels, connector keying, and red-stripe/Pin 1 identification--to make proper connection as blindingly obvious as possible. You'd almost have to be asleep not to be able to figure out how this cable plugs in and to what!

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