Maximum PC white paper RSS Feed

White Paper: OLED Screens

Nathan Edwards — Mon, 02 Nov 2009 14:02:23 -0600

Organic light-emitting diode (OLED) screens offer better picture quality and draw less power than traditional LCDs. But what are OLEDs?

Organic light-emitting diodes, or OLEDs, are often touted as the next big thing in display technology, offering brighter colors, true black, lower power consumption, and better off-axis viewing than traditional LCD screens. They’ve popped up in gadgets from high-concept to mundane: The infamous Optimus Maximus keyboard, for example, utilizes many tiny OLED screens in its programmable and customizable keycaps, and both Sony’s new X-series Walkman and Microsoft’s new Zune HD have OLED screens. OLED technology has made great strides in the past 10 years, and cheaper and better manufacturing processes mean they’ve started appearing in everything from media players to phones to high-definition televisions—even keyboards. But what are OLEDs?

What’s Inside

In the simplest terms, LEDs (light-emitting diodes) emit light by running an electrical current through a diode. Diodes create unidirectional electric flow, moving electrons from the negatively charged cathode to the positively charged anode, creating electron holes, or spaces where electrons could be. Electrons flowing in drop into these holes and emit light. An organic light-emitting diode uses the same principle, but between the cathode and anode are two layers of organic semiconductor compounds: the emissive layer, near the cathode, and the conductive layer, near the anode (organic compounds are chemical compounds that contain carbon). The cathode sends (negatively charged) electrons into the emissive layer, while the anode draws electrons from the conductive layer, leaving positively charged “electron holes.” This creates a negatively charged emissive layer and a positively charged conductive layer, which attract each other, drawing electron holes to the emissive layer. The positive-charged holes and negative-charged electrons recombine, lowering the energy levels of the electrons, emitting light as a by-product. Simple, right?

From a development standpoint, OLEDs have a lot of potential. Organic chemistry is a fairly well-understood science—reds, blues, and greens were developed in a much shorter time frame in OLEDs than in regular LEDs. And new molecules that can be used in the layers, which have longer lifetimes and produce brighter colors, are being discovered frequently.

In an OLED, an electrical current causes electrons (-) to move from the cathode to the emissive layer, creating a negative charge in the emissive layer. The positively charged anode attracts electrons from the conductive layer, creating a positive charge in the conductive layer, which recombine with holes (+) in the conductive layer attract electrons from the emissive layer, which recombine with the electron holes, lowering the energy level of the electrons and emitting light as a by-product.

It turns out that OLEDs are great for use in displays, because the organic molecules that comprise the emissive and conductive layers can be deposited in very thin, large sheets onto a variety of substrates—from glass to metal to fiber—so that millions of individual OLEDs can be crammed together, row by row and column by column, into a very small space. Each of these OLEDs becomes one pixel of the display. The organic compounds can be deposited using several methods, depending on the type of organic molecule used in the display.

There are two types of OLEDs currently in production and development, differentiated by the size of the molecules in their organic compounds. Small-molecule OLEDs are usually manufactured via organic vapor phase deposition (OVPD)—the organic molecules are evaporated and carried via inert gas, then deposited on a substrate through a series of very small nozzles held near the substrate’s surface. Large-molecule, or polymer OLEDs, can be created via a process similar to inkjet printing—the polymers are dissolved into a solution and “printed” onto the substrate.

Advantages & Disadvantages

The advantages of OLEDs over traditional LCDs are many. First, unlike liquid-crystal displays, OLED pixels actually emit light, so they don’t require backlighting. Traditional LCD screens often utilize traditional LEDs or CCFLs for backlighting, which—in addition to increasing the thickness of the display to accommodate a light source—prevents the display from rendering true black, as even “black” LCD pixels are backlit. Since OLED pixels produce light when on and don’t produce light (or draw power) when off, a darker, richer black can be created. Having light-emitting pixels also enables richer colors, a broader color gamut, higher contrast, and a greater viewing angle than an LCD screen. Because “off” pixels don’t draw power, and because there’s no need for a separate light source, OLED displays require less energy to run. And because the organic molecules can be printed onto a variety of substrates, flexible displays are possible.

OLEDs, however, are not without their disadvantages. The manufacturing process is still expensive, so large OLED displays are rare—most OLEDs are used in small-screen applications, such as media players and smartphones, though HD displays up to 40-inches have been demonstrated. And the materials used in OLEDs don’t necessarily last as long as regular LCD displays—another reason they’re more frequently found on phones and media players, rather than computer monitors and televisions. Monitors are typically turned on for much longer stretches of time. And finally, the organic materials in OLEDs are extremely susceptible to water damage, so displays must be well-sealed.

OLED to the Future

What’s next for OLED technology? The European Union, among others, is investigating the use of OLEDs as cheap solid-state lighting to replace incandescent bulbs. Their stated goal is to create a 100x100cm square of OLED material that creates 100 lumens per watt of power, has a working lifespan of at least 100,000 hours, and costs less than 100 euros per square meter to produce.

OLEDs have found their way into concept cars, lighting fixtures, PMPs, and laptop prototypes, with the latter expected to enter production by Q3 2010. As manufacturing processes become less expensive, OLED displays could start to replace LCDs, not just in media players and phones, but also in notebook computers, monitors, and televisions, on a much larger scale.

White Paper: Building a Modern CPU

Loyd Case — Mon, 12 Oct 2009 12:30:00 -0500

From concept to design to manufacturing and everything in between, the processor inside your rig was years in the making

Designing and manufacturing a modern CPU is a huge project. It requires both backward compatibility and an understanding of where PC workloads are going in the future—a delicate balancing act made more difficult by the huge engineering staffs and massive dollar outlays involved. Let’s take a look at the steps needed to build a Core i7 or AMD Phenom II processor.

Before the manufacturing plant starts churning out chips, there are a few critical preliminary steps. Prior to the first circuit being laid out or the first simulation run, the designers need to know exactly what it is they’re designing. This phase takes input from many sources. Marketing gets involved, with predictions of what users will need when the CPU actually ships, usually two to four years in the future. Engineering and performance teams feed in billions of traces of actual applications being run on current-gen CPUs, so the designers can see how existing CPUs perform under real-world conditions.

The Design Process

After the specification phase, the design phase begins in earnest. Design involves creating a design document, validating the design with simulations, and laying out the design.

The architecture team begins by defining how the CPU is supposed to work. How many registers will it have? What’s the power budget? How many cores? How much cache? These and thousands of smaller details are all ironed out in the design document, which becomes the bible from which the final product is created.

Once the design is in place, it needs to be tested. How do you test a CPU that doesn’t exist yet? You run simulations. There are specific programming languages that chip designers use to build simulations of a CPU. Actual code is compiled and run on the simulated CPU, albeit much more slowly than on the final product. Those applications-code traces collected during the specification process are re-run on the simulation to make sure everything works as expected.

In the layout phase, the real process of building the CPU begins. Engineers use special software to route circuits into patterns that can then be processed in the lithography step. With high-performance PC processors, some elements of the logic layout are hand-tuned, while other aspects, such as cache line layout, may be automated. Chip companies often have prebuilt blocks in libraries that can just be dropped into the overall CPU layout.

Today’s processors also utilize multiple layers of semiconductors. Each layer needs to be laid out so that it can be connected to the others. The primary goal of the layout step is to create circuit patterns that are efficient yet simple enough that they can be manufactured. The first draft of the design undergoes verification, which runs more virtual tests on the layout to make sure connections are correctly made and circuits completed. The final layout is known as tape out, where the layout is compiled into an industry standard format and sent to manufacturing.

Note that these design-phase steps aren’t linear. Simulations, for example, will be run constantly, up until the first working silicon returns from the fab. Design is an iterative process, continuing to the point when the first chips come off the assembly line.

The Manufacturing Process

Here’s where we get into the physical processes of building our CPU. First, ultra-pure wafers of silicon are coated with the conductive material that will make up the final circuitry. Then the chip is baked at temperatures above 200 degrees C to remove any water or volatile contaminants.

Building a chip is essentially a photographic process. Photoresist—material that is light sensitive—is applied uniformly to the wafer, usually by spraying it onto the wafer while it’s spinning at high speed. The layer must be thin and very uniform. Once applied, the chip is again baked to dry the photoresist and make it more uniform.

(click to enlarge)

The lithography step marks the chip’s design on the wafer by exposing the photoresist to light of specific frequencies. These intense beams of light, which shine through masks, define the layout of the circuits on the chip. Note that these beams are very narrow, so either the beam scans across the wafer, or the wafer is moved slightly (stepped) under the light beam. Today’s modern process technologies often use a hybrid of the scanning and stepping techniques. Another bake cycle removes imperfections left over from the lithography process.

The develop step removes the exposed photoresist, leaving behind patterns of circuits. Now the wafer has a layer of material with narrow “channels” laid out in the pattern of the CPU circuitry. But these patterns are not yet circuits. Next, chemicals are applied to the wafer that permanently remove the now exposed conductive material, which was initially coated on the chip in the wafer prep phase. The photoresist still on the chip resists the etching process, so only the circuit patterns are implanted into the wafer substrate.

The final step in the actual chip making process is stripping the remaining photoresist from the wafer surface. What’s left are many dies on the wafer, cleaned and ready to be processed.

Final Steps

Next, the entire wafer is tested to ensure it meets quality standards. The dies are then cut and sent to the packaging line, where the different layers are assembled into the chip packages we’re all familiar with. During the packaging process, function and validation tests are performed, which allow the manufacturer to sort according to clock speed and functional bins. This is where a Core 2 Quad Q9650 may be differentiated from a lower-clocked Q9550, for example.

Of course, this is a simplified overview of the process for building a modern CPU. You can find more details at websites including entries on Wikipedia for photolithography, photoresist, wafer creation, and more. One fairly technical, but still understandable overview of the lithography process can be found at Lithoguru (www.lithoguru.com/scientist/lithobasics.html).

White Paper: DirectX 11

Michael Brown — Wed, 30 Sep 2009 14:00:00 -0500

You thought DX10 brought big changes? Get a load of DX11!

DirectX 10 marked a radical departure from DirectX 9: In order to be compatible, a graphics processor must feature a unified architecture in which each shader unit is capable of executing pixel-, vertex-, and geometry-shader instructions. The changes in DirectX 11 aren’t quite as fundamental, but they could have just as big an impact—and not only with games.

DirectX 11 is a superset of DirectX 10, so everything in DirectX 10 is included in the new collection of APIs. In addition, DX11 offers several new features and three additional stages to the Direct3D rendering pipeline: the Hull Shader, the Tessellator, and the Domain Shader. And in an effort to deliver cross-hardware support for general-purpose computing on graphics processors, Microsoft has come up with a new Compute Shader.

DirectX 11 will be compatible with both Vista and Windows 7, but many of its graphics features will be available on GPUs designed for previous iterations of Direct3D. Tapping into the Tessellator’s power, however, will require a GPU with transistors dedicated to the task (in this sense, DX11 marks a slight departure from DX10’s vision of a unified architecture). Let’s explore the concept of tessellation now.

Meet Tess

The three new pipeline stages we mentioned earlier are all related to tessellation. They reside in the geometry-processing stage, between the Vertex Shader and the Geometry Shader. Tessellation can rapidly create the primitive elements that go into the creation of a complex three-dimensional object by subdividing just a few at a time. In this case, the primitives are called patches, which are defined by control points (visualize Photoshop’s pen tool, except that DX11’s control points manipulate a surface instead of a line). Patches replace the triangles used in previous versions of DirectX. Each subsequent subdivision creates more primitives, with each group being smaller than the last. Increasing the number of primitives in a model makes that model look more realistic. The Tessellator can also reshape these primitives by adjusting the control points to form more complex geometry.

While it’s very easy for GPUs to produce coarse objects like cubes, they have a much harder time creating objects with smooth curves. By tessellating a coarse object, a cube, for example—a GPU can transform that object into something that does have smooth curves, such as a sphere—and the kicker is that this process requires relatively little GPU horsepower and graphics memory.

(click to enlarge)

Here’s a broad overview of how tessellation works: The Vertex Shader outputs patches, which then travel down the pipeline to the Hull Shader. The Hull Shader analyzes the patches’ control points to determine how the Tessellator should be configured (generating so-called “tessellation factors”) and then sends the patches on to the Tessellator. The Tessellator, in turn, subdivides the patches and feeds a stream of points to the Domain Shader. The Domain Shader manipulates these points to form the appropriate geometry and sends the resulting vertices to the Geometry Shader.

Hardware tessellation isn’t a new concept. Animators at Pixar began using tessellation to create their highly detailed characters beginning with A Bug’s Life, and they’re still using it today. The GPU that AMD designed for Microsoft’s Xbox 360 gaming console features a tessellation unit, and AMD integrated something similar in its Radeon GPUs for the PC, beginning with the Radeon HD 2000 series. This led many to predict that Microsoft would expose tessellation in DirectX 10. But that didn’t happen, and DirectX 11 won’t be able to tap AMD’s tessellator, either, because AMD’s original implementation of the technology isn’t compatible with Microsoft’s.

I Compute, Therefore I Am

If you’ve followed the evolution of modern GPUs, you know that they’ve moved from being single-core processors designed for one specific purpose—processing graphics—to massively parallel devices with hundreds of processing cores. Modern GPUs are capable of performing more than a trillion floating-point operations per second, which has been a boon for the types of graphics processing and real-time animation needed for computer gaming. But this hardware can be tapped to perform other types of computations, too; the concept is known as GPGPU computing (the acronym stands for general-purpose graphics processing unit). Most software applications, however, as well as the tools used to develop them, are designed for serial execution, not parallel.

GPGPU computing, therefore, requires brand-new tools, and AMD and Nvidia have invested significant amounts of time and effort to both create them and spur the development of GPGPU applications. AMD’s initiative is known as Stream SDK (Software Development Kit) and Nvidia’s is called CUDA (Compute Unified Device Architecture). The growth of GPGPU computing, however, has been hindered by the fact that each company’s tools work with only that company’s GPU. Microsoft hopes to change that with the addition of the Compute Shader to DirectX 11. The Compute Shader will enable developers to write GPGPU code that will run on any graphics processor, be it Nvidia’s GeForce platform, AMD’s Radeon, or Intel’s upcoming Larabee.

Although the Compute Shader is integrated with DirectX 11, it’s not actually a stage in the Direct3D pipeline. It can, however, take data structures from the Pixel Shader stage, manipulate them using the GPU’s resources, and then apply them to the final image in a post-processing stage. Microsoft has identified a range of target applications specifically related to graphics processing that should improve games, including effects physics (particles, smoke, water, cloth, etc.), ray tracing, gameplay physics, and even AI.

Analysts expect the first DirectX 11–compatible GPUs to reach the market in the fourth quarter; games that take advantage of DirectX 11 aren’t expected until sometime in 2010.

White Paper: Media Container File Formats

Michael Brown — Thu, 24 Sep 2009 14:30:42 -0500

Meet the digital equivalent of Tupperware for your music and video files

When can a file encapsulate more than one type of data? When it’s a metafile, wrapper, or container file. You might think of a container file as a package or envelope in which other files are housed. Zip files, which can contain documents, photos, videos, software programs, and many other types of files, are one type of container that you encounter frequently.

We’ll limit our discussion here to media container formats. A pure container file specifies how the data is stored, but it doesn’t necessarily know how it was compressed or encoded or even what is required to play back those files. This can lead to confusion when dealing with container files wrapped around media because there’s a chance that the media player you’re using is capable of opening the container but not equipped with the algorithm required to decode the files inside. Although a container can theoretically hold any type of data, most are optimized during development to wrap around particular data groups, e.g., digital audio for music; static images for digital photographs; or digital video interleaved with digital audio, plus subtitles, closed-caption information, and chapter data for movies. Container formats that support video also include the information required to synchronize the various data streams in the file during playback.

The MP4 container, which is based on Apple's QuickTime technology, encapsulates audio, video, and synchronization information in a series of packages within packages.

Container files store data in chunks, packets, or segments; three terms that describe essentially the same concept. A chunk’s primary content is known as its payload, and most container formats arrange their chunks in sequence, with a file header at the beginning of each chunk that describes the type of data contained in the payload. This arrangement makes it easier to recover lost chunks in the event of file corruption or dropped frames.

Common Media Containers

WAV is a common example of a container format that’s used exclusively for audio on the Windows platform, although the container is also compatible with the Linux and Macintosh operating systems. WAV containers typically host uncompressed linear pulse code modulation (LPCM) audio files encoded in RIFF (Resource Interchange File Format). When you rip a CD to your hard drive, the file is converted from the Red Book audio format and saved as a WAV file on your hard drive, although most people then convert that file to another, less storage-intensive format using a lossy code such as MP3, or a lossless one such as FLAC.

If you’ve ever ripped a movie from a DVD (or just examined the directory structure on a DVD), you’ve encountered VOB files (the acronym stands for Video Object). VOB files are containers that house a DVD’s digital video and audio streams, plus menus and data streams such as subtitles. There is typically one VOB file for each title on the disc, although this is not a requirement. VOB files are in turn based on the MPEG Program Stream, a container format that multiplexes packetized digital audio, video, and data streams (these are individually known as elementary streams). Elementary streams are packetized by dividing the stream into sequential bytes and encapsulating them in packet headers.

Movies on Blu-ray discs, on the other hand, utilize a container based on the MPEG Transport Stream. Just like MPEG-PS, MPEG-TS multiplexes packetized digital audio, video, and data streams and synchronizes their output; the key difference is that MPEG-TS supports a mechanism for error correction. MPEG-TS is also used in the U.S. for ATSC digital television broadcasts.

Apple’s QuickTime container (which uses the file extension MOV) can host multiple audio, video, effects, and text tracks (for subtitles). MOV files are unique among media containers in that each track can contain either a digital media stream or a reference to a media stream contained in a separate file. This latter feature renders QuickTime very well-suited to editing because the media doesn’t need to be rewritten after an edit. QuickTime also forms the basis of the MPEG-4 Part 14 container (which uses the file extension MP4). Both MOV and MP4 containers can use the same MPEG-4 codecs, but MP4 is more widely supported because it’s an international standard.

Other popular container formats include AVI (Audio Video Interleave), an aging but ubiquitous Microsoft standard that can contain many types of audiovisual data, including MPEG-4; Ogg, the standard container for audio encoded with the open-source Vorbis codec and video encoded with the open-source Theora codec; and RealMedia, the standard container for RealNetworks’ RealVideo and RealAudio files.

But no discussion of media container formats would be complete without mentioning the Matroska Multimedia Container. This ambitious open-standard and royalty-free file format (its ownership resides in the public domain) can hold an unlimited number of media tracks in a single file. Unlike the other container formats we’ve covered, which are limited to certain types of audio and video files encoded using particular codecs, Matroska containers can harbor audio and video files encoded using virtually any codec (MPEG-4, H.264, MP3, FLAC, WMA, and more—including Dolby TrueHD and DTS-HD, the HD audio formats used on Blu-ray discs). MKV files are used to store video files, MKA files to store audio-only files, and MKS files are used for subtitles. Matroska containers can also support chapter divisions, subtitles, menus, and metadata and tags.

White Paper: Internet Protocol

Michael Brown — Wed, 26 Aug 2009 16:10:48 -0500

Let's dig into the layer cake that is the Internet

Conceptually speaking, the Internet can be viewed as consisting of four functional layers: the Link Layer, the Internet Layer, the Transport Layer, and the Application Layer. Each layer has several protocols, sets of rules that define how data is formatted and transmitted, which are known collectively as the Internet Protocol Suite. We’ll discuss all four layers here, but we’ll dive deepest into the Internet Layer and its associated Internet Protocol (IP)—because this is the worldwide network’s most fundamental component.

The Link Layer is the lowest layer and is responsible for delivering data over whatever hardware is in use. A link consists of the physical and logical components that are used to interconnect host computers and other types of network nodes (a node is any electronic device that’s connected to the network, including hosts). Link Layer protocols, including Address Resolution Protocol and Media Access Control, operate only on a host’s link.

When you interact with the Internet—by accessing a website, downloading a file, streaming media, and so forth—your communications flow through four network layers, each of which has several protocols designed for the task at hand. Internet Protocol, which comes into play on the Internet Layer, defines the structure and addressing of data packets traveling over the network.

The Internet Layer sits on top of the Link Layer, but we’ll return to it later since its collection of protocols includes Internet Protocol, the primary focus of this white paper. The Transport Layer comes next, and it is responsible for encapsulating blocks of data into packets—an information payload bracketed by control information that informs the network how to deliver the data—and delivering it to the appropriate application program running on the host computer. The two most common protocols used in the Transport Layer are Transport Control Protocol (TCP) and User Datagram Protocol (UDP).

The Application Layer is the highest level of the Internet’s architectural model, and it contains all the protocols concerned with process-to-process communications via an IP network. You’ll likely be familiar with many of the protocols that operate at this level, since they include HTTP (HyperText Transfer Protocol), FTP (File Transfer Protocol), POP3 (Post Office Protocol, version 3), and even BitTorrent.

Internet Protocol

Internet Protocol (IP) defines addressing methods and packet structures and is used to deliver packets from a source host to a destination host based on the hosts’ respective addresses. Internet Protocol is considered a connectionless protocol because, unlike a voice telephone network, it doesn’t rely on a circuit being established before one host can transmit packets to another.

Internet Protocol can be used on heterogeneous networks, meaning that information can travel over any combination of Ethernet, ATM, Wi-Fi, Token Ring, and many other types of networks. Version 4 (IPv4) is the most common version of Internet Protocol in use today, but its successor (IPv6) is being deployed rapidly; the two coexist in the meantime.

The genius of Internet Protocol lies in its assumption that the entire network infrastructure is both inherently unreliable and dynamic: Links and nodes can disappear at any time while new links and nodes are constantly coming into existence, but none of this can prevent a data transmission from reaching its destination.

The Internet is designed according to an end-to-end principle: The bulk of its intelligence is located at the ends of its transmission paths; the routers in between simply forward packets to the next closest gateway based on the ultimate destination’s address. Because of this, Internet Protocol provides only what’s known as “best effort delivery,” meaning that it does not guarantee that data will be delivered or that the user can expect any particular quality of service. In fact, packets can be corrupted, duplicated, arrive in a different order from that in which they were sent (perhaps because one took a longer path), or be lost altogether without the node at either end of the transmission path being notified.

IPv4 can ensure that the IP packet header is free from errors by computing a checksum at each routing node, but IPv6 dropped this feature in order to increase the speed at which packets travel through network routers. In any event, it is the responsibility of upper-layer protocols—such as TCP—to correct reliability issues, such as data corruption, lost or duplicate packets, and out-of-order packet delivery.

IP Addresses

The primary difference between IPv4 and IPv6 resides in their address systems. A unique IP address is assigned to every device participating in the network. These are stored as binary numbers, but typically displayed in a human-readable format: 208.77.188.166, for instance. IPv4 uses a 32-bit structure (capable of establishing four billion unique addresses), while IPv6 uses a 128-bit scheme (capable of creating 340 undecillion unique addresses—an undecillion is a one followed by 36 zeroes).

As private local-area networks began to proliferate in the 1990s—primarily in homes and businesses—it began to look as though the world might run out of IPv4 addresses, so a set of private IP addresses was set aside and reserved exclusively for that purpose (private IPv4 addresses range from 192.168.0.0 to 192.168.255.255). Unlike a conventional IP address, a private IP address is not assigned to a specific individual or organization and it can be used without the approval of a regional Internet registry.

Using a technique known as IP masquerading, an entire collection of private network addresses can be hidden behind a single public IP address that is assigned to a specific individual or organization. Since private IP addresses cannot be routed on the public Internet, network address translation (NAT) is used to modify the IP address contained in the packet header as the packet passes through the router, so that it matches that public IP address. A process called port forwarding can be used to allow traffic from the Internet to reach hosts with private IP addresses within the masqueraded network.

White Paper: Surge Suppression

Michael Brown — Wed, 19 Aug 2009 17:00:00 -0500

Stamp out power surges before they stomp on your PC

The surge suppressor is one of the unsung heroes of the computer world. Often valued more for its ability to multiply one electrical receptacle into many than for its role as protector of all things electronic, the surge suppressor is your first line of defense against transient power surges that can damage or destroy sensitive components inside your PC. Let’s take a look at how they work.

Before we tackle the concept of surge suppression, we should first understand what exactly a surge is. In the United States, electrical energy flows through standard household wiring at an average rate of 120 volts. Because the system used is alternating current, the voltage level of every AC cycle reaches a peak value that’s roughly 1.414 times higher than 120 volts. A surge occurs when the voltage level suddenly rises significantly higher than that. A lightning strike on a power line, for instance, will cause a transient spike in the electrical power entering your house. Problems with your utility company’s equipment (anything from a downed power line to a defective transformer) can also cause power surges.

Appliances and other electrically powered devices inside your home, however, are much more common causes of power surges. Any device that requires a large amount of energy to switch on or off—examples include refrigerators, vacuum cleaners, and air conditioners—can disrupt the flow of voltage through your home’s electrical wiring. Surges such as these don’t pack as much destructive power as a lightning strike, but they can cause as much damage, instantly or over time.

As abnormally high voltage surges into the outlet strip, the MOVs respond by decreasing their resistance, channeling the excess voltage to ground. As the surge diminishes, the MOVs' resistance increases so that the correct amount of voltage reaches the receptacles.

The First Line of Defense

When you plug a surge suppressor into an electrical outlet in your wall, it will pass the electrical current from your home’s wiring to each of the devices plugged into its several receptacles. But the current will first pass through at least one component called an MOV, which stands for metal oxide varistor. If the voltage entering the MOV is higher than a specified value, the MOV will conduct the extra electricity either to the surge suppressor’s neutral wire or to its grounding wire.

An MOV consists of a mass of metal oxide grains (typically zinc oxide, with small amounts of bismuth, cobalt, and manganese) sandwiched between two metal plates that function as electrodes. One electrode is connected to the surge suppressor’s hot wire (the one carrying the electrical current) and the other is connected to its neutral or ground wire. These electrodes exhibit variable resistance (hence the term “varistor”) dependent on the voltage passing through them.

When the voltage is below a defined level, the electrodes present very high resistance, so the current bypasses the MOV and runs through to the outlet strip’s receptacles. When the voltage exceeds that defined level, the electrodes change character and present very low resistance. At this point, the MOV absorbs some of the excess current (dissipating the energy in the form of heat) and conducts more of it to the ground wire to bleed off the excess voltage. As the surge passes and the voltage in the hot wire returns to normal, the MOV reverts to its previous state of high resistance.

Surge Suppressor Ratings

A surge suppressor’s clamping voltage rating specifies the amount of voltage that will cause its MOVs to conduct electricity into its ground wire. A reputable manufacturer will submit its surge suppressor to Underwriters Laboratory for testing according to its UL 1449 standard. A lower value indicates better protection, but 330 volts is the minimum clamping value a manufacturer can claim according to the UL standard. A surge suppressor’s joule rating, which defines now much energy it can absorb and/or dissipate before it fails, provides a second means of measuring its effectiveness at smoothing energy spikes. In this case, a higher number indicates better protection.

There will always be a slight delay before a surge suppressor can respond to a power surge; the longer the delay, the longer the devices connected to it will be exposed to the surge. Fortunately, surges also take a few microseconds to reach their peak voltage, which gives the surge suppressor time to react. A suppressor with a one-nanosecond response time will be fast enough to shield connected devices from damaging energy spikes.

MOVs degrade after responding to a few major surges or many smaller ones. A fully degraded MOV offers no protection, but it also won’t prevent power from reaching the outlets. A high-quality surge suppressor will include a thermal fuse or a circuit breaker that can cut off power if a particularly strong surge exceeds the MOVs’ capacity to absorb it or redirect it to ground. A good surge suppressor will also feature an LED to indicate that its MOVs remain viable. When the LED fails to light, the surge suppressor should be replaced.

White Paper: HDMI

Michael Brown — Tue, 21 Jul 2009 15:00:00 -0500

Dive into the details of this high-definition video interface

HDMI (the acronym stands for High-Definition Multimedia Interface) is one of the consumer electronics industry’s more remarkable innovations. This de facto HDTV interface enables the transmission of high-definition digital video, up to eight channels of digital audio, HDCP encryption, the Consumer Electronics Control (CEC) protocol, and five volts of electrical power over a single cable.

HDMI 1.0, introduced in December 2002, had all of these features. The latest version, HDMI 1.3c, boasts several more, including support for Deep Color, auto lip sync, and the two high-definition multichannel audio formats used in Blu-ray discs. Let’s take a look at how HDMI accomplishes all this while remaining backward-compatible with the earlier DVI standard.

As the Version Turns

As with DVI, HDMI relies on Transition Minimized Differential Signaling (TMDS) to encode and transmit digital video, but HDMI uses TMDS to encode and transmit digital audio as well. TMDS uses a technique called differential signaling to reduce electromagnetic interference, which enables signals to travel faster with less chance of error.

The sending device—a Blu-ray disc player, for instance—encodes the digital signal and transmits it along with an inverse copy using two separate bundles of copper wire (as with Cat-5 Ethernet cables, HDMI uses twisted-pair wiring to reduce noise. Noise induced in one half-twist has a propensity to cancel noise induced in a neighboring half-twist). The receiving device—an HDTV, for example—decodes the signal, measures the difference between it and the inverse copy, and uses this information to compensate for any in-transit signal loss.

Each new version of the HDMI standard has used the same basic type of cable and the same 19-pin connector, but each iteration has increased the standard’s bandwidth capabilities and introduced new features (some of which are optional). HDMI 1.0, for instance, supported a maximum pixel clock rate of 165MHz (4.95Gb/s of bandwidth), which was sufficient for delivering HDTV at 1080p at a 60Hz refresh rate and WUXGA resolution (1920x1200), also at a 60Hz refresh rate.

HDMI 1.1 added support for DVD Audio and HDMI 1.2 added support for Super Audio CD. HDMI 1.3 more than doubled the pixel clock rate to 340MHz (bandwidth of 10.2Gb/s), which enabled even higher-resolution displays, such as WQXGA (2560x1600), using a single digital link. Type A HDMI connectors (the most common) and Type C connectors (designed for digital camcorders) use single links; a Type B HDMI connector uses a dual link, but since the single-link connectors are capable of such high bandwidth, Type B connectors are not currently in production.

HDMI 1.3 also added support for Deep Color and the xvYCC color space. Deep Color describes a method of using an extremely high number of shades, hues, and luminosity to increase the number of colors that can be displayed from millions to billions. Deep Color utilizes 30-, 36-, or 48-bit depths, compared to the 24-bit color on tap in HDMI 1.0. The xvYCC color space, also known as x.v.Color, represents color using the full range of values (0 to 256) in an 8-bit space. RGB colors are represented by a subset of the values (16 to 235) in an 8-bit space in order to compensate for the limitations of analog displays.

Audio Enhancements

HDMI 1.0 supports eight channels of LPCM (linear pulse code modulation) encoded at sampling rates up to 192kHz and with 24-bit resolution. HDMI 1.3 added support for eight-channel surround-sound streams encoded using the lossless compression algorithms Dolby TrueHD and DTS-HD Master Audio. All HDMI versions carry the older Dolby Digital and DTS lossily compressed bit streams, too.

Complex video processing can sometimes cause latency, resulting in the audio signal arriving at its destination before the video signal does. When this occurs, the actors in the movie will look as though they’re speaking a different language and the soundtrack was poorly dubbed. HDMI 1.3 added a feature called auto lip sync that can automatically prevent this from happening.

All HDMI versions support a set of control functions known as CEC (Consumer Electronics Control) commands, although the specifications for the commands themselves weren’t completely spelled out until HDMI 1.2a was finalized. CEC commands utilize HDMI’s capacity for bidirectional communication to permit a single remote control to operate multiple devices connected with an HDMI cable. One-touch play, for instance, will
automatically trigger the necessary commands for the entire home-theater system to power up and begin playing when the Blu-ray disc player’s Play button is pushed. The addition of a few CEC commands and a few arcane details are all that distinguish HDMI 1.3 from HDMI 1.3a, 1.3b, and 1.3c.

Know Your Options

When shopping for HDMI equipment, be aware that some features—including support for Deep Color, the xvYCC color space, and even Dolby TrueHD and DTS-HD Master Audio—are optional. Although the HDMI spec does not spell out a maximum cable length, there are two types of HDMI 1.3 cable: Standard, or Category 1, cable has been tested to perform at speeds of 75MHz, which is the equivalent of a 1080i signal. Such cables typically max out at about five meters (16 feet) and are manufactured using 28 AWG copper wire, although neither of these factors are part of the official HDMI 1.3 spec.

A cable certified as High Speed or Category 2 has been tested to perform at speeds of 340MHz and can handle 1080p signals and increased color depths. High Speed HDMI cables can also accommodate higher-resolution displays (e.g., 2560x1600). These cables are manufactured using heavier gauge wire—26- or even 24 AWG—and are capable of running longer distances.

Longer cable runs can be achieved by using repeaters, which use electrical power to boost the HDMI signal; “active” cables, which operate in a similar fashion; and extenders, which use fiber-optic or Cat-5 cable.

(click to enlarge)

White Paper: How BitTorrent Works

Michael Brown — Fri, 10 Jul 2009 10:00:15 -0500

How peer-to-peer file-sharing networks work

BitTorrent is a tremendously popular peer-to-peer file-sharing protocol designed to simplify and speed up the process of transferring large files over the Internet while drastically limiting the bandwidth consumption of any one server.

In a conventional file-transfer process, a file is stored on a server on a network such as the Internet. Other computers on the network send messages to the server, informing it that they would like to copy that file. When the two sides establish a connection, the other computers become clients to the server. As the number of clients increases, so do the demands on the server. And while each client might consume only a little bandwidth, the server can consume tremendous amounts. To reduce costs and prevent the server from crashing, the server’s owner will typically constrain the speed at which each client is allowed to download data or even limit the number of clients that can be served at one time.

In the original BitTorrent, one computer acted as a tracker to coordinate the peer-to-peer file-transfer process. The tracker maintained a list of which computers on the Internet were in the process of uploading or downloading pieces of the seed file. A trackerless BitTorrent system eliminates this central computer by distributing the tracker data amongst the swarm participants.

Napster and Gnutella

Peer-to-peer file sharing eliminates the need for a central server to host files. The original Napster, however, still relied on a central server to keep track of connected computers and the files available on them. That’s how the service ran afoul of copyright laws and was eventually forced to shut down: Napster’s servers didn’t store copyrighted material, but the courts decided that Napster’s service violated the Digital Millennium Copyright Act because the company knowingly facilitated copyright infringement.

While the Napster lawsuit was underway, another peer-to-peer network named Gnutella sprang up and completely eliminated the centralized server. When you launch a Gnutella client, it immediately searches the Internet for other computers running Gnutella clients. Each of these peers is called a node. When you initiate a file search, the Gnutella client queries each node to determine if it’s hosting the file you’re looking for. If these nodes don’t have the file you’re searching for, they’ll send queries to the nodes they’re connected to. The node that does have the file will send a response message back to the node that initiated the search, and the user can then decide whether or not to download it.

Gnutella has two significant shortcomings: First, it relies on file transfers between just two peers. Since the most common means of consumer Internet access—cable and DSL—use asynchronous connections in which download speeds are much higher than upload speeds, the peer downloading the file is limited to whatever speed the peer uploading the file is capable of. Second, it depends on users to reciprocate, but it can’t force anyone who downloads files from other people’s computers to allow others to download files from their machines. Netiquette frowns on this practice, which is known as leeching, but Gnutella can’t prevent it.

BitTorrent

BitTorrent cleverly avoids the legal and practical problems associated with peer-to-peer file-sharing networks like Gnutella and the original Napster. It allows one peer to rely on several others for file transfers, rendering the process both faster and cheaper for all the peers involved, and it has a reward system that encourages user reciprocation.

Rather than establish a relationship between just two peers, the BitTorrent protocol simultaneously gathers pieces of a file from several peers that already have the file or that are in the process of obtaining it. It then downloads these pieces to your computer and reassembles them on your hard drive when all the pieces have been acquired.

The BitTorrent protocol depends on at least one peer making the entire file available to the network; this is known as the “initial seed.” As other peers begin downloading this seed file, they simultaneously upload pieces of the file to other peers that are looking for it. Each peer is encouraged to continue making the file available after they’ve downloaded it in its entirety, in effect creating additional seeds. A BitTorrent client can facilitate this with a tit-for-tat scheme that rewards reciprocation by giving preference to peers that send data back.

To share a file, the user first creates a smaller file, called a “torrent,” that contains metadata about the file and the “tracker” computer that will coordinate the file distribution. The metadata inside the torrent file varies according to the BitTorrent client that created it, but the file will have an “announce” section that specifies the tracker computer’s URL, and an “info” section containing file names, file sizes, and a hash code for each piece of the file (more on this later).

Any peer that wants to download the file must first download the torrent file associated with it. The torrent will connect the peer to the appropriate tracker, which will in turn tell the peer which other peers are currently downloading the file. All the peers actively engaged in sharing a particular file are referred to as a “swarm.” The more peers in the swarm, the faster each peer will be able to download the file. In a conventional client-server relationship, a file in high demand can be slow to download because it presents a hardship for the servers hosting the file. With BitTorrent, a file’s popularity actually increases the speed at which it can be downloaded.

Each peer distributing a file breaks it into chunks ranging from 64KB to 4MB in size and creates a checksum for each chunk using a hashing algorithm. When another peer receives these chunks, it matches its checksum to the checksum recorded in the torrent file to verify its integrity.

A “trackerless” BitTorrent system has no central computer coordinating the file sharing; instead, every peer acts as a tracker. In this case, the BitTorrent client employs a distributed hash table to keep track of the location of the initial seeds, checksums, and peers actively engaged in the swarm.