iPod Image GalleryThe sixth-generation iPod Classic
Photo courtesy Apple
The sixth-generation iPod Classic. See more iPod pictures.

In 2001, Apple introduced the iPod, an MP3 player with the unheard-of storage capacity of 5 gigabytes. Six iPod generations later, the iPod plays songs, movies, games and photo slideshows, and you can store up to 160 GB of any type of file you want. The evolution has been a lesson in consumer electronics marketing and development: Millions of people are so hooked on the iPod, they continue to buy it and its coordinating Apple products despite quick battery death and difficult repairs.

The 2007 iPod release, the sixth-generation iPod classic, is a digital audio player, video player, photo viewer and portable hard drive, making it a full-fledged portable media center. It's available in 80-GB and 160-GB capacities and has a color LCD screen. In addition to the iPod classic, there are several other devices in the current generation of iPod players:

* iPod touch, announced in September 2007, is a touch-screen iPod with an 8-GB or 16-GB capacity. It looks a lot like an iPhone, and it uses the iPhone's multi-touch user interface. You can learn all about the technology in How the iPhone Works.
* iPod shuffle, with a 1-GB capacity, plays only songs and has no display.
* iPod nano plays digital audio, displays digital photos and comes in 4- and 8-GB capacities. It has a 2-inch display screen and a smaller form factor than the iPod video.





Although the iPod is an Apple product, it works with both Mac and Windows machines. Since it's the top-selling media player in the United States, probably the big question is: What makes it different from any other digital media player The answer will differ depending on who you ask. Some might say it's the form factor -- the 80-GB iPod classic is less than half an inch (1.4 centimeters) deep and weighs about 4.9 ounces (140 grams) . For comparison, the Zen Portable Media Center from Creative is 1.06 inches (2.7 centimeters) deep, weighs 12 ounces (340 grams) and has only 20 GB of hard drive space.

Other people might tell you it's the Apple Click Wheel, a wheel that makes it incredibly easy to navigate through the various menus and options with just a thumb. According to Apple CEO Steve Jobs in a Newsweek interview, "It was developed out of necessity for the Mini, because there wasn't enough room [for the buttons]. But the minute we experienced it we just thought, 'My God, why didn't we think of this sooner?'" And then, some might tell you the greatest thing in the world is the super-tight iPod/iTunes integration (which, ironically, others will curse until the day they die).

iTunes is the integrated jukebox/media-player software that comes with an iPod. It lives on your computer, and you use it for organizing, playing, converting and downloading files from an external source to your computer and from your computer to an iPod. This is really no different from the software than comes with any other portable media player. The thing that makes iTunes a brilliant invention from a consumer-electronics standpoint is the built-in iTunes Store that keeps iPod users coming back to Apple on a regular basis. Anyone who owns an iPhone or an iPod touch can also shop at the iTunes store usiconnection.

­ The iTunes Store lets iPod users purchase music, movies, podcasts, audiobooks and music videos with a click -- it's an integral part of the iTunes software. You can watch or listen to the files through iTunes on your computer and download them to your iPod. And you don't even have to drag and drop: The iTunes software autosyncs with iPod whenever it's connected to your computer through a USB 2.0 port (you can use FireWire for charging, but not for syncing). Just plug it in, and the iPod automatically downloads every new file that you added to your iTunes jukebox since the last time it was connected. It also uploads to iTunes all new data that you added to your iPod since last the two conversed, like playlists and song ratings.

iPod Features

• Audio
  The 160-GB iPod stores up to 40,000 songs (20,000 for the 80-GB model). The search function lets you type in keywords (song name, artist, album) using the Click Wheel to locate a song on the iPod hard drive. It supports MP3, WAV, AAC, AIFF, Apple Lossless and Audible audio files. You can download songs from the iTunes Store, from a different MP3 download site or rip them from your CDs into the iTunes software. You need to go through the iTunes software to download files to the iPod (unless you download a hack that lets you bypass iTunes -- more on hacks in the Software section). You can listen to audio books at various speeds -- normal, faster or slower -- without seriously distorting the sound, and connect your iPod to your home stereo through a mini-to-RCA jack. The device comes with equalizer presets for different music styles.

Photo courtesy Apple The iPod touch foregoes the standard Click Wheel in favor of multi-touch sensing.

• Video­ The 80-GB version holds up to 100 hours of video, and the 160-GB version holds up to 200 hours. It supports H.264 and MPEG-4 files as well as MOV files converted to iPod-friendly video through the iTunes software. You can play video podcasts, music videos, feature films and TV shows on the iPod, plus your own DVDs and home videos that you encode using QuickTime Pro and download to your player through iTunes.

• Photos
  The player holds up to 25,000 photos. It supports files converted from JPEG, BMP, GIF, TIFF, PNG and PSD. You can download your photos to the iPod from Mac iPhoto or Windows Adobe Photoshop Elements/Album. Using an RCA or S-video connection (S-video through the dock accessory), you can connect the iPod to your home-theater TV to watch photo slideshows (complete with soundtrack) or video on a larger screen.

• External hard drive
  The iPod can function as portable hard drive, carrying all file types between computers. Just choose "enable disk usage" in the iTunes software, and you can load whatever you want onto the player's hard disk.

• Calendar/contacts syncing
  iPod automatically downloads all new contact/calendar data added to Mac iCal or Microsoft Outlook/Outlook Express since the last time iPod was connected to your computer.

iPod Hardware

In addition to a cracked LCD, the iPod we're dissecting is nice and scratched.

Before we take apart our iPod video, there are a couple of things you should know. First, the screen on this iPod is cracked. Since no one at HowStuffWorks volunteered their perfect little iPod as a subject for this author's screwdriver, we turned to eBay to find a damaged unit we could take apart with good conscience. Which brings us to the second thing you should know: iPods are almost as valuable broken as they are in mint condition. After several last-minute outbids, we found out we had to pay about $200 for a 30-GB iPod video with a cracked LCD -- this was the typical ending price for this type of unit. And a brand-new, sixth-generation one costs $249 and has more storage space. We were left shaking our heads. Are hundreds of people writing articles that incorporate an iPod dissection? Are hundreds of people that addicted to tinkering with high-priced electronics? Are iPods really so hard to get fixed by Apple once the one-year warranty runs out? The New York Times article "Good Luck With That Broken iPod" (February 4, 2006) would suggest the latter, although it's really anybody's guess.

That said, let's pry this baby apart.

For most of the iPod video's functionality, we're dealing with seven primary components:

• Hard drive - 30-GB Toshiba 1.8-inch hard drive
• Battery - rechargeable lithium-ion (700 mAh, 3.7V)
• Click Wheel - navigation via touch-sensitive wheel and mechanical buttons
• Display - 2.5-inch TFT LCD
• Microprocessor - PortalPlayer PP5021C with dual ARM7TDMI cores
• Video chip - Broadcom BCM2722
• Audio chip - Wolfson Microelectronics WM8758 codec

The case actually isn't that difficult to get into -- we used a 6-inch metal putty knife to pry apart the seam. Once you see that you need to get the knife under the thin edge of one side of the casing (instead of driving it straight down), it comes apart pretty quickly. Here's what we saw when we pulled it apart:

This iPod video uses a 30-GB Toshiba 1.8-inch hard drive (model MK3008GAL), featuring 4200 rpm and a USB interface. It weighs 1.7 ounces (48 grams) and fits 30 GB onto a single platter, squeezing in 93.5 gigabits per square inch. To fit so much into so little space, the drive uses smaller and lighter sliders (which keep the right spacing between the read/write heads and the recording surface) and a more sensitive thin-film technology on the heads and the platter. The increased sensitivity allows for a greater number of recorded bits per square inch.

When you remove the front casing, you're looking at the LCD, the motherboard and the Click Wheel:

The Click Wheel is a section unto itself, and we'll deal with that technology on the next page. Let's start here with the iPod video display.

The display is a 2.5-inch, 16-bit, TFT LCD. It has a 320x240-pixel resolution and a 0.156 dot pitch. The screen is incredibly thin -- just 0.125 inches (3.175 mm) deep.

The connectors used in the iPod are miniscule. Instead of the plastic connectors you find in larger devices, the ends of the wires that connect the various components of the iPod are coated in a film that stiffens them to create a viable input. Here you can see where the LCD connects to the back side of the motherboard (with a U.S. dime for reference):

All of the chips and memory devices that make an iPod run are situated on the motherboard. Here's the front:

And here's the back:

In the image above, you can see the Click Wheel controller. A "mixed-signal array" is a chip that can deal with both analog and digital data. In the case of the Click Wheel, the controller has to accept analog data generated by the movement of a finger over the surface of the wheel and turn it into digital data the microprocessor can understand. Let's find out how it does that.

The Thing About the Battery iPod's battery is completely built-in -- you can't just pop in a couple of new AA batteries when it stops charging. This built-in battery has been a headache both for iPod owners and for Apple.

Originally, the iPod battery was not only non-user-replaceable, but it was also very expensive to replace via Apple. When your battery died (sometimes within a year of buying the iPod), you had to send your iPod to Apple for a replacement, and the new battery cost $100. A lot of bad press and a class-action lawsuit later, Apple's iPod battery-replacement program costs $59. The class-action suit was settled, and iPod owners listed in the suit were compensated with $50 vouchers and partial refunds for their $100 battery replacement.

Apple defends the use of a non-user-replaceable battery by explaining that the built-in battery allows for the ultra-slim form factor for which the iPod is known.

• Games
  iPod comes with pre-loaded games. You can also download games from the iTunes store, from third-party companies or even create your own (see the "iPod Software" section).

• Car integration
  If you have an iPod and you're in the market for a new car or a new head unit receiver, you can get one that fully integrates your player into the sound system. There are manufacturer-built car stereos that support iPod integration to the level that you can control the device through the head-unit or steering-wheel controls.

iPod Click Wheel

The Click Wheel is a touch-sensitive ring that you use to navigate through all of iPod's menus and control all of its features. It provides two ways to input commands: by sliding your finger around the wheel and by pressing buttons located under and in the middle of the wheel.

Under the plastic surface of the Click Wheel, there are four mechanical buttons (Menu, back, forward, play/pause), and there's one button in the center (select).

Click Wheel face

Behind the Click Wheel face (left) and Click Wheel contacts on the motherboard

You've got five buttons and five corresponding contacts on the motherboard. When you press, say, the right side of the wheel while you're listening to a song, the wheel pushes down the forward button. The underside of each rubber button is metal, so pressing it completes the corresponding circuit on the motherboard. The motherboard tells the processor this circuit is complete, and the processor tells the operating system to fast-forward through the song.

The Click Wheel's touch-sensitive function lets you move through lists, adjust volume and fast forward through a song by moving your finger around the stationary wheel. It works a lot like a laptop touchpad. In fact, the company that supplied the Click Wheel for the 4G iPod was Synaptics, most widely known for making laptop touchpads. For the 5G, Apple created its own proprietary Click Wheel design based on the same capacitive sensing principle as the previous Synaptics-designed Click Wheel.

Under the plastic cover of the Click Wheel, there is a membrane embedded with metallic channels. Where the channels intersect, a positional address is created, like coordinates on a graph.

At its most basic, a capacitive-sensing system works like this: The system controller supplies an electrical current to the grid. The metal channels that form the grid are conductors -- they conduct electricity. When another conductor -- say, your finger -- gets close to the grid, the current wants to flow to your finger to complete the circuit. But there's a piece of nonconductive plastic in the way -- the Click Wheel cover. So the charge builds up at the point of the grid that's closest to your finger. This build-up of an electrical charge between two conductors is called capacitance. The closer the two conductors are without touching, the greater the capacitance.

Front of membrane: Here you can see the conductive grid

Back of membrane: Here you can see the Click Wheel controller.

The "sensing" part of the system comes in with the controller. The Click Wheel controller (see above) is programmed to measure changes in capacitance. The greater the change in capacitance at any given point, the closer your finger must be to that point. When the controller detects a certain change in capacitance, it sends a signal to the microprocessor. As you move your finger around the wheel, the charge build-up moves around the wheel with it. Every time the controller senses capacitance at a given point, it sends a signal. That's how the Click Wheel can detect speed of motion -- the faster you move your finger around the wheel, the more compacted the stream of signals it sends out. And as the microprocessor receives the signals, it performs the corresponding action -- increasing the volume, for instance. When your finger stops moving around the wheel, the controller stops detecting changes in capacitance and stops sending signals, and the microprocessor stops increasing the volume.

Now, in discussing the workings of the Click Wheel, a particularly curious HowStuffWorks staffer raised the following question: If your finger controls the Click Wheel because your finger is a conductor, why can't you control the Click Wheel with a paper clip?