20 more technical terms every Mac user should know

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.

Audio formats

The audio world hasn’t escaped the alphabet soup of acronyms. You’re sure to encounter a number of these audio formats on the Mac as well as on the Web.

AIFF (Audio Interchange File Format): Audio files broadly come in two flavors—compressed and uncompressed. Compressed files are usually missing data that you can’t easily hear (though if you compress a file enough, you’ll certainly hear the difference). Uncompressed audio files reproduce the audio without performing tricks to remove data. They are therefore larger than compressed files.

AIFF files, which were originally developed by Apple, are uncompressed. AIFF files are supported by iTunes and used by professionals and others who seek the highest audio quality.

WAV (Waveform Audio File Format): This is another uncompressed audio file format. It was developed by Microsoft and IBM, and is more commonly found on Windows computers, though Macs can use them as well.

iTunes supports the most common audio formats.

MP3 (MPEG-1 or MPEG-2 Audio Layer III): MP3 files are compressed, and were quite popular in the early days of digital music because of their reduced file size. They continue to be used quite commonly today by many music services and devices. QuickTime, iTunes, and the Mac support MP3.

AAC (Advanced Audio Coding): AAC is another lossy compression format and one that’s gaining popularity. It’s the format for music you buy from the iTunes Store, and it’s Apple’s default format for encoding music within the iTunes application. AAC is widely used in other settings as well—on YouTube and in Nintendo DSi and PlayStation 3 game consoles.

AAC has gained popularity because it’s believed to produce better-sounding audio files at lower bit rates (the number of bits processed over time—the higher the bit rate, the better the sound, but also the larger the file). AAC files on the Mac are generally denoted by their .m4a extension. Tracks purchased from the iTunes Store that are copy protected (Apple dropped copy protection a few years ago) have a .m4p extension.

Apple Lossless: Although the name says “lossless,” these files are compressed (don’t ask). The resulting file size is between 40 and 60 percentthe size of the original uncompressed version and sounds indistinguishable from it (cue the audiophiles). Apple Lossless is supported by the Mac and OS X as well as by iOS devices.

WMA (Windows Media Audio): This is Microsoft’s lossy compression audio format. It’s not supported at all on iTunes for the Mac, though the Windows version of iTunes will convert WMA files to MP3 or AAC format for compatibility with iOS devices. At one time WMA files littered the Web, but because they’re not compatible with many of today’s devices, you see them less often.

Video formats

As with audio, video formats abound as well. The Mac supports the most common ones. They include:

MPEG-4: This is a broad standard that defines methods of video and audio compression. There can be variations in the MPEG-4 files you encounter, and these variations are based on the “part” designation. For instance, MPEG-4 part 2 uses a variety of codecs (which stands for compressor-decompressor)—technologies that compress and make movies playable on a variety of devices. Part 2 codecs tend to be older and are used in DivX, Xvid, 3ivx, and Apple’s QuickTime 6 technologies.

MPEG-4 part 10 is more modern and uses H.264 encoding, which produces smaller files that still look quite good. Today’s iTunes and QuickTime—and applications that rely on QuickTime (iMovie and Final Cut Pro, for example)—are compatible with the H.264 standard. Videos you find in iTunes usually bear the .m4v extension, indicating that they’re compressed using this codec.

QuickTime movies: QuickTime is far more than just an application or the engine that iTunes uses to play videos. It’s a layer of the Mac operating system that handles many of the Mac’s multimedia chores. In this discussion, however, we’re talking about the .mov files that QuickTime produces. QuickTime movie files are containers. And by that I mean that they can take advantage of a variety of codecs. You can, for example, create one QuickTime movie that uses the H.264 codec and another that employs Apple’s ProRes codec, yet both can have the .mov extension.

As a container, QuickTime supports a wide variety of codecs.

The important thing to know is that files that bear the .mov extension can almost always be played with QuickTime Player and iTunes. You must convert them before you can play them on an iPod or iOS device, however, as these devices don’t natively support .mov files.

AVI (Audio Video Interleaved): This is another movie container format—one made by Microsoft. Thanks to the more-universal MPEG-4 variations, AVI movies are disappearing from the Web.


You can’t throw a brick at the Internet without hitting yet another arcane acronym. And because you can’t, this series could go on forever. But it won’t, because, FWIW, YAIHBWTSOT (You And I Have Better Ways To Spend Our Time.)

One of those ways is for me to take a vacation. Class dismissed until July 25th!

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