20 more technical terms every Mac user should know

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Last week I introduced you to 20 computer terms you should know. In addition to a few “thanks for that” responses, I also received a few “Yeah, but what about…” queries. And each is worth our time. So, have another round on me.


Not all hardware devices have simple names like printer and keyboard. A few go by their acronyms.

UPS: I know, I know, UPS is commonly thought of as standing for United Parcel Service. But in this case it’s uninterruptible power supply. A UPS is like a large powerstrip. The difference is that it holds a battery. When you plug a device into a UPS and, sometime later, the power goes out, that device will continue to draw life-sustaining electricity from the battery.

If you have a lot of devices plugged in to that UPS—your computer, a monitor, a modem, a router, and a printer, for example—there’s a very good chance that its battery will drain in short order. For this reason, you should be careful about what you plug in to it (you might skip the printer, for example). Even then, a UPS isn’t intended to substitute for a solid power connection. Instead, it’s a safety measure—designed to allow you enough time to shut down your gear as you normally would (versus having it shut down the second the power blinks out, which can result in data corruption). I wouldn’t run my gear without one.

NAS: No, this has nothing to do with auto racing. Rather, NAS stands for network-attached storage. This is a box that contains some variety of storage device (one or more drives). As its name implies, it’s available to your computer via your local network (there are wireless as well as wired NAS devices). A NAS device is a limited computer in that it runs its own operating system and can act as a mail, Web, and media server.

Synology makes a popular line of NAS devices.

The advantage of a NAS device is that any other device on the local network can access it (and many devices can access it over the Internet). That means that if you have three Macs, an iPhone, and an iPad, all of these devices can access the files on the NAS system. You can, for example, store your iTunes library on the NAS unit and then point every one of your Macs to it so that you needn’t have multiple copies of your library spread among your computers. You could also direct all of your Macs to back up to the NAS device.

RAID: This isn’t the bug spray or the late-night action you’ve planned on your neighbor’s pantry. RAID stands for redundant array of independent disks. A RAID is made up of multiple disks that, to your computer, behave like a single disk. You can set up a RAID in a variety of ways. One of the most common is to configure the drives so that data is duplicated between them. In such a configuration, if one of your drives fails, your data is still intact because it also lives on another, still-operational drive. In such a configuration you may have two 3GB drives (totalling 6GB), but your Mac will see only a 3GB capacity, because the RAID has created two copies of your data.

You can also configure a RAID in a JBOD (just a bunch of disks) arrangement. You can use a JBOD in a couple of ways. The most common is to take all the disks and sum their capacity into a single storage destination (called concatenating or summing). So, if you have those two 3GB drives in your RAID, your Mac will see a total capacity of 6GB, since the RAID is storing just a single copy of the data on the combined drives. Or you can treat them as separate volumes or two of them as a combined volume and one of them as a separate volume. As "just a bunch of disks" it's supposed to be flexible.

MIDI: It’s possible to send music data from a keyboard, drum pad, or specially configured guitar using a scheme called MIDI (Musical Instrument Digital Interface). For example, if you attach a MIDI keyboard to your Mac and fire up GarageBand, you can use that keyboard to play GarageBand’s on-board sounds.

The important thing to understand about MIDI is that it isn’t sending sound to your Mac. Rather it’s sending instructions. In essence its commands say “Play Middle C for two beats and then stop. Now play the E above and hold down the sustain pedal.” The application it’s talking to will respond to those instructions by making sound.

With a MIDI keyboard, you can “play” your computer.

At one time you sent MIDI data over a MIDI cable (with a largish round connector with five pins) that was attached to a MIDI interface that was, in turn, connected to your Mac with a USB or FireWire connection. These days, many MIDI instruments bear a USB connector, allowing you to plug your instrument directly into your Mac.

Archive formats

It’s possible to pack a group of files and folders into a single file (or archive). Here are a two archive formats you might encounter.

Zip: This is common lossless data-compression file format that was originally found most often on Windows computers. Now supported on the Mac, these are the file archives you’re most likely to receive via email. It’s a popular format not only because it can make large files smaller (though already-compressed files such as JPEG images don’t shrink), but also because it’s used by both Apple and Microsoft. (Zip files are not, however, supported on iOS devices.) Zipped files bear the .zip extension.

DMG (Apple Disk Image): DMG is an Apple format, and files archived this way will have a .dmg extension. Unlike zip files, which, when double-clicked, open to a single file or folder, disk-image files mount as volumes, much like a USB key drive you’d plug into your Mac. Apple software that you download is often archived using this format. Additionally, using a tool such as Disk Utility, you can create password-protected disk image archives.

Image formats

Hang out in this digital world long enough and you’ll hear terms like JPEG, TIFF, Raw, PNG, GIF (or maybe even giff) float past your ears. These are all image formats, but each one is distinct. Let’s take a look.

JPEG (Joint Photographic Experts Group): JPEG (pronounced JAY-peg and showing a .jpg file extension) is one of the most common image formats around. It’s routinely used for Web-based images as well as images produced by digital cameras. It’s common because just about any device that can display an image is compatible with these images. Also JPEG images use lossy compression (meaning that some of the image’s data has been stripped out) and therefore the files are small in comparison to some other file types.

GIF (Graphics Interchange Format): If you find arguments over the number of angels capable of dancing on a pin’s head not rancorous enough, take a vocal stand on the pronunciation of this acronym. The fact that the first letter stands for Graphics, hinting that it should be pronounced with a hard G—giff—hasn’t convinced the format’s founder that it shouldn’t be pronounced with a soft-G sound—as in jiff. There is no right answer (except mine, of course, and I’m not saying one way or the other).

GIF images are also widely found. They generally support just 256 colors, so they’re not suitable for photographs. It’s possible to store multiple images within a single GIF file and then “play” those files in repeated sequencial order, which allows you to create animations with them. If you’ve seen a smallish repeating animated image on a webpage (someone’s avatar in a forum, for example), it’s likely a GIF.

PNG (Portable Network Graphics): This format was created as an alternative to GIF (because of patent tussles). It’s a lossless compression format that supports far more colors than GIF and is commonly used on the Web. Although it supports lots of colors, it’s not suitable for professional print work, as it doesn’t support certain professional-quality color standards. When you take a screenshot with your Mac (by pressing Command-Option-3) or iOS device (by pressing the Home and On/Off button together), you produce a PNG image.

TIFF (Tagged Image File Format): The Tagged in the file’s acronym gives you a hint of what TIFF offers. In addition to being suitable for high-end graphics applications (and the native format for scanners), TIFF files can also contain data. For example, it might include information about the geometry of the image. It can also act as a container for holding a JPEG image. At one time, digital cameras offered a TIFF option for those who wanted to save high-quality versions of their pictures, but camera manufacturers now use raw files (see below) for this kind of thing.

Raw: What, no acronym? No. Raw is a description. It tells you that the file holds as much information about the image as the camera’s sensor can capture. Some people refer to raw files as “digital negatives” because they’re not something you can print from directly. Instead, they must be converted to a format such as TIFF or JPEG, much as you’d print a picture from a negative. But prior to saving an image in one of these formats, you can tweak it to within an inch of its life using a compatible image editor. There are hundreds of raw image formats, which explains why applications like iPhoto may not be able to process a raw image from a brand-new camera (if that camera is using yet another new raw format). Apple routinely updates the OS to support new raw formats.

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