Random access memory

Random access memory (usually known by its acronym, RAM) is a type of computer data storage. Today it takes the form of integrated circuits that allow the stored data to be accessed in any order, i.e. at random. The word random thus refers to the fact that any piece of data can be returned in a constant time, regardless of its physical location and whether or not it is related to the previous piece of data.This contrasts with storage mechanisms such as tapes, magnetic discs and optical discs, which rely on the physical movement of the recording medium or a reading head. In these devices, the movement takes longer than the data transfer, and the retrieval time varies depending on the physical location of the next item.

History:
An early type of widespread writable random access memory was the magnetic core memory, developed in 1949-1951, and subsequently used in most computers up until the development of the static and dynamic integrated RAM circuits in the late 1960s and early 1970s. Before this, computers used relays, delay lines or various kinds of vacuum tube arrangements to implement "main" memory functions (i.e. hundreds or thousands of bits), some of which were random access, some not. Latches built out of vacuum tube triodes, and later, out of discrete transistors, were used for smaller and faster memories such as registers and (random access) register banks. Prior to the development of integrated ROM circuits, permanent (or read-only) random access memory was often constructed using semiconductor diode matrixes driven by address decoders.

Types of RAM:
RAM generally store a bit of data in either the state of a flip-flop, as in SRAM (static RAM), or as a charge in a capacitor (or transistor gate), as in DRAM (dynamic RAM), EPROM, EEPROM and Flash. Some types have circuitry to detect and/or correct random faults called memory errors in the stored data, using parity bits or error correction codes. RAM of the read-only type, ROM, instead uses a metal mask to permanently enable/disable selected transistors, instead of storing a charge in them.

iPOD

iPOD is a popular brand of portable media players designed and marketed by Apple Inc. and launched on October 23, 2001. As of 2008, the current product line-up includes the hard drive-based iPod Classic, the touchscreen iPod Touch, the video-capable iPod Nano, the screenless iPod Shuffle and the iPhone. Former products include the compact iPod Mini and the spin-off iPod Photo (since re-integrated into the main iPod Classic line). iPod Classic models store media on an internal hard drive, while all other models use flash memory to enable their smaller size (the discontinued mini used a Microdrive miniature hard drive). As with many other digital music players, iPods, excluding the iPod Touch, can also serve as external data storage devices. Storage capacity varies by model.Apple's iTunes software can be used to transfer music to the devices from computers using certain versions of Apple Macintosh and Microsoft Windows operating systems. users who choose not to use Apple's software or whose computers cannot run iTunes software, several open source alternatives to iTunes are also available. iTunes and its alternatives may also transfer photos, videos, games, contact information, e-mail settings, Web bookmarks, and calendars to iPod models supporting those features. Apple focused its development on the iPod line's unique user interface and its ease of use, rather than on technical capability. As of September 2007, more than 150 million iPods had been sold worldwide, making it the best-selling digital audio player series in history.

SOFTWARE:

The iPod line can play several audio file formats including MP3, AAC/M4A, Protected AAC, AIFF, WAV, Audible audiobook, and Apple Lossless. The iPod Photo introduced the ability to display JPEG, BMP, GIF, TIFF, and PNG image file formats. Fifth and sixth generation iPod Classics, as well as third generation iPod Nanos, can additionally play MPEG-4 (H.264/MPEG-4 AVC) and QuickTime video formats, with restrictions on video dimensions, encoding techniques and data-rates. Originally, iPod software only worked with Mac OS; iPod software for Microsoft Windows was launched with the second generation model. Unlike most other media players, Apple does not support Microsoft's WMA audio format — but a converter for WMA files without Digital Rights Management (DRM) is provided with the Windows version of iTunes. MIDI files also cannot be played, but can be converted to audio files using the "Advanced" menu in iTunes. Alternative open-source audio formats, such as Ogg Vorbis and FLAC, are not supported without installing custom firmware onto an iPod .
During installation, an iPod is associated with one host computer. Each time an iPod connects to its host computer, iTunes can synchronize entire music libraries or music playlists either automatically or manually. Song ratings can be set on an iPod and synchronized later to the iTunes library, and vice versa. A user can access, play, and add music on a second computer if an iPod is set to manual and not automatic sync, but anything added or edited will be reversed upon connecting and syncing with the main computer and its library. If a user wishes to automatically sync music with another computer, an iPod's library will be entirely wiped and replaced with the other computer's library.

Sun Microsystems

Sun Microsystems is a multinational vendor of computers, computer components, computer software, and information technology services, founded on 24 February 1982.^[4] The company is headquartered in Santa Clara, California (part of Silicon Valley), on the former west campus of the Agnews Developmental Center.

Products include computer servers and workstations based on its own SPARC processors as well as AMD's Opteron and Intel's Xeon processors; storage systems; and, a suite of software products including the Solaris Operating System, developer tools, Web infrastructure software, and identity management applications. Other technologies of note include the Java platform and NFS.

Sun is a proponent of open systems in general and UNIX in particular and a major contributor of open source software.^[5]

Sun's manufacturing facilities are located in Hillsboro, Oregon and Linlithgow, Scotland.

HISTORY

The initial design for what became Sun's first Unix workstation, the Sun 1, was conceived by Andy Bechtolsheim when he was a graduate student at Stanford University in Palo Alto, California. He originally designed the SUN workstation for the Stanford University Network communications project as a personal CAD workstation. It was designed as a 3M computer: 1 MIPS, 1 Megabyte and 1 Megapixel. It was designed around the Motorola 68000 processor with an advanced Memory management unit (MMU) to support the Unix operating system with virtual memory support^[6], He built the first ones from spare parts obtained from Stanford's Department of Computer Science and Silicon Valley supply houses.^[7]

On February 12, 1982 Vinod Khosla, Andy Bechtolsheim, and Scott McNealy, all Stanford graduate students, founded Sun Microsystems. Bill Joy of Berkeley (a primary developer of BSD), joined soon after and is counted as one of the original founders^[8]. The Sun name is derived from the initials of the Stanford University Network. Sun was profitable from its first quarter in July 1982.

Sun's initial public offering was in 1986 under the stock symbol SUNW, for Sun Workstations (later Sun Worldwide).^[9][10] The symbol was changed in 2007 to JAVA; Sun stated that the brand awareness associated with its Java platform better represented the company's current strategy.^[11]

Sun's logo, which features four interleaved copies of the word sun, was designed by professor Vaughan Pratt, also of Stanford University. The initial version of the logo had the sides oriented horizontally and vertically, but it was subsequently redesigned so as to appear to stand on one corner.

The first Sun workstations ran a Version 7 Unix System port by UniSoft on 68000 processor-based machines.

The "Bubble" and its aftermath

During the dot-com bubble, Sun experienced dramatic growth in revenue, profits, share price, and expenses. Some part of this was due to genuine expansion of demand for web-serving cycles, but another part was synthetic, fueled by venture capital-funded startups building out large, expensive Sun-centric server presences in the expectation of high traffic levels that never materialized. The share price in particular increased to a level that even the company's executives were hard-pressed to defend. In response to this business growth, Sun expanded aggressively in all areas: head-count, infrastructure, and office space.

The bursting of the bubble in 2001 was the start of a period of poor business performance for Sun.^[12] Sales dropped as the growth of online business failed to meet predictions. As online businesses closed and their assets were auctioned off, a large amount of high-end Sun hardware was available very cheaply. Much like Apple, Sun relied a great deal on hardware sales.

Multiple quarters of substantial losses and declining revenues have led to repeated rounds of layoffs,^[13][14][15] executive departures, and expense-reduction efforts. In December of 2001 the share price dropped to the 1998 pre-bubble level of about one hundred dollars or so and then kept going, a rapid fall even by the standards of the high tech sector at that time. The stock dipped below 10 dollars a year later, one-tenth of its 1990 value, then quickly bounced back to 20, where it has hovered ever since. In mid-2004, Sun ceased manufacturing operations at their Newark, California facility and consolidated all of the company's US-based manufacturing operations to their Hillsboro, Oregon facility, as part of continued cost-reduction efforts.^[16] In 2006 Sun closed the Newark campus completely and moved 2,300 staff to its other campuses in the area.^[17]

Many companies (like E-Trade and Google) chose to build Web applications based on large numbers of the less expensive PC-class x86-architecture servers running Linux, rather than a smaller number of high-end Sun servers. They reported benefits including substantially lower expenses (both acquisition and maintenance) and greater flexibility based on the use of open-source software. That trend is slowing and may be reversing,^{[citation needed]} given (1) the throughput and efficiency of Sun's new horizontally-scaled systems (see below) and (2) the fact that both Sun's flagship Solaris operating system and its UltraSPARC T1 processor are now fully open-source.

Higher level telecoms control systems such as NMAS and OSS service predominantly use Sun equipment. This use is due mainly to the company basing its products around a mature and very stable version of the Unix operating system and the support service that Sun provides.

SURFACE COMPUTER

Microsoft Milan Surface Computer

The latest trend in computer interaction is touch. From Jeff Han's where multi-touch user interfaces got their first big public airing to the impending iPhone launch, everyone's thinking of innovative ways to control their machines just using your fingers. Microsoft is no exception—today they've announced the first product from what they're calling their Surface Computing group, a tabletop computer for retail outlets that's been code-named Milan. And we've got a hands-on report, with photos and video—right after the jump, of course.

It's an acrylic table that's 22 inches high, with a 30-inch horizontal display. Remember those tabletop arcade games in bars in the 80s? It looks something like that. Inside, there's a PC running Vista, a projector, and an array of cameras that track objects and touch on the surface of the screen. With a little special programming sauce, it all comes together in a very slick experience.

For instance, you can take a digital camera that's Wi-Fi enabled, put it down on the tabletop, and the machine recognizes it and downloads the photos. Then, you can interact with them much like actual physical photos—you can pass them around the table, shuffle them into piles to sort them, pull on the corners to zoom in or out. It's intuitive, quick, and brings a fun social aspect to a task (photo editing) that can be the very definition of tedious.

We've had a chance to play with Milan twice—once at CES in January, and once last week. They're demoing other slick applications. The Music application turns the table into a virtual jukebox, letting you drag songs onto a shared playlist that could power the music at a bar or restaurant. There's a Concierge application that helps you pull together an itinerary for a day out in a strange city, complete with recommendations and great looking maps.

The major focus of this first generation device is at retail and in bars and hotels. The launch partners, who will be rolling out the machines in November, are Harrah's Entertainment, Sheraton Hotels, and T-Mobile.

The T-Mobile demo was interesting. They'll be installing the machines in T-Mobile stores, and the idea is that it's something between a traditional retail experience and a website. You'll place a phone on the unit, and it will pop up not only the price, but information about the phone. You'll be able to flip through service plans and options, and when you find what you're looking for, you'll drag it onto the phone, and it will be added. At the end, you hit check out, and the phone is provisioned, and delivered to your house. It's slick.

The Microsoft folks I talked to about Milan thing that the surface computing market is a multi-billion dollar business, potentially, and having seen the demos, I think they might be right. But there are more than a few barriers to overcome. Right now, the machine is using a series of tags on some physical objects to recognize them -- that's not going to fly in the real world. The Milan team is going to have to get a lot of manufacturers and other companies to do something to help identify their gadgets.

And Microsoft is launching the platform in a very constrained way. Right now, as I've said, it's just for big retail clients, which means that you won't have a Milan coffee table any time soon, although that might be the real killer app here. Imagine controlling a Media Center PC like this, or doing interactive slideshows at your house.

This is some exciting technology, and I'm really interested to see how people react to it. I'm not going to go out and say that it's going to change the world (remember the Segway hype?), but it's innovative and intriguing, and nice to see from a company who we tend to criticize for a lack of those traits. —Mark McClusky

Bonus: Check out our Milan coverage elsewhere on Gadget Lab and on Epicenter. And scroll down for a couple of videos showing the tabletop in action.

MAC OS

Mac OS is the trademarked name for a series of graphical user interface-based operating systems developed by Apple Inc. (formerly Apple Computer, Inc.) for their Macintosh line of computer systems. The Macintosh user experience is credited with popularizing the graphical user interface. The original form of what Apple would later name the "Mac OS" was the integral and unnamed system software first introduced in 1984 with the original Macintosh, usually referred to simply as the System software.

Apple deliberately downplayed the existence of the operating system in the early years of the Macintosh to help make the machine appear more user-friendly and to distance it from other operating systems such as MS-DOS, which were portrayed as arcane and technically challenging. Much of this early system software was held in ROM, with updates typically provided free of charge by Apple dealers on floppy disk. As increasing disk storage capacity and performance gradually eliminated the need for fixing much of an advanced GUI operating system in ROM, Apple explored cloning while positioning major operating system upgrades as separate revenue-generating products, first with System 7 and System 7.5, then with Mac OS 7.6 in 1997.

Earlier versions of the Mac OS were compatible only with Motorola 68000-based Macintoshes. As Apple introduced computers with PowerPC hardware, the OS was upgraded to support this architecture as well. Mac OS X, which has superseded the "Classic" Mac OS, is compatible with both PowerPC and Intel processors.

Versions

The early Macintosh operating system initially consisted of two pieces of software, called "System" and "Finder", each with its own version number.^[1] System 7.5.1 was the first to include the Mac OS logo (a variation on the original "Happy Mac" smiley face Finder startup icon), and Mac OS 7.6 was the first to be named "Mac OS" (to ensure that users would still identify it with Apple, even when used in "clones" from other companies).

Until the advent of the later PowerPC G3-based systems, significant parts of the system were stored in physical ROM on the motherboard. The initial purpose of this was to avoid using up the limited storage of floppy disks on system support, given that the early Macs had no hard disk. (Only one model of Mac was ever actually bootable using the ROM alone, the 1991 Mac Classic model.) This architecture also allowed for a completely graphical OS interface at the lowest level without the need for a text-only console or command-line mode. A fatal software error, or even a low-level hardware error discovered during system startup (such as finding no functioning disk drives), was communicated to the user graphically using some combination of icons, alert box windows, buttons, a mouse pointer, and the distinctive Chicago bitmap font. Mac OS depended on this core system software in ROM on the motherboard, a fact which later helped to ensure that only Apple computers or licensed clones (with the copyright-protected ROMs from Apple) could run Mac OS.

The Mac OS can be divided into two families of operating systems:

• "Classic" Mac OS, the system which shipped with the first Macintosh in 1984 and its descendants, culminating with Mac OS 9.
• The newer Mac OS X (the "X" refers to the Roman numeral, ten). Mac OS X incorporates elements of OpenStep (thus also BSD Unix and Mach) and Mac OS 9. Its low-level BSD-based foundation, Darwin, is free software/open source software.

"Classic" Mac OS (1984-2001)

Original 1984 Macintosh desktop

Main article: Mac OS history

The "classic" Mac OS is characterized by its total lack of a command line; it is a completely graphical operating system. Heralded for its ease of use and its cooperative multitasking, it was criticized for its very limited memory management, lack of protected memory, and susceptibility to conflicts among operating system "extensions" that provide additional functionality (such as networking) or support for a particular device. Some extensions may not work properly together, or work only when loaded in a particular order. Troubleshooting Mac OS extensions can be a time-consuming process of trial and error.

The Macintosh originally used the Macintosh File System (MFS), a flat file system with only one level of folders. This was quickly replaced in 1985 by the Hierarchical File System (HFS), which had a true directory tree. Both file systems are otherwise compatible.

Extensions Manager under Mac OS 9

Most file systems used with DOS, Unix, or other operating systems treat a file as simply a sequence of bytes, requiring an application to know which bytes represented what type of information. By contrast, MFS and HFS gave files two different "forks". The data fork contained the same sort of information as other file systems, such as the text of a document or the bitmaps of an image file. The resource fork contained other structured data such as menu definitions, graphics, sounds, or code segments. A file might consist only of resources with an empty data fork, or only a data fork with no resource fork. A text file could contain its text in the data fork and styling information in the resource fork, so that an application which didn't recognize the styling information could still read the raw text. On the other hand, these forks provided a challenge to interoperability with other operating systems; copying a file from a Mac to a non-Mac system would strip it of its resource fork.

The Classic OS is still supported and Classic Applications Support was shipped in addition to OS X with PowerPC (but not Intel) Macs until early 2006. However, Intel-based Macintoshes cannot run the Classic system or applications, nor can PowerPC models that have been upgraded to Mac OS 10.5 Leopard.

Mac OS X (2000-present)

Main article: Mac OS X

Mac OS X brought Unix-style memory management and pre-emptive multitasking to the Mac platform. It is based on the Mach kernel and the BSD implementation of UNIX, which were incorporated into NeXTSTEP, the object-oriented operating system developed by Steve Jobs' NeXT company. The new memory management system allowed more programs to run at once and virtually eliminated the possibility of one program crashing another. It is also the second Macintosh operating system to include a command line (the first is the now-discontinued A/UX, which supported classic Mac OS applications on top of a UNIX kernel), although it is never seen unless the user launches a terminal emulator.

However, since these new features put higher demands on system resources, Mac OS X only officially supported the PowerPC G3 and newer processors, and now has even higher requirements (the additional requirement of built-in USB (10.3) and later FireWire (10.4)). Even then, it runs somewhat slowly on older G3 systems for many purposes.

For over three years now, Mac OS X has gotten faster with every release — and not just "faster in the experience of most end users", but faster on the same hardware. This trend is unheard of among contemporary desktop operating systems.^[2]

PowerPC builds of Mac OS X include a compatibility layer for running older Mac applications, the Classic Environment. This runs a full copy of the older Mac OS, version 9.1 or later, in a Mac OS X process. PowerPC-based Macs shipped with OS 9.2 as well as OS X. OS 9.2 had to be installed by the user — it was not installed by default on hardware revisions released after the release of Mac OS X 10.4. Most well-written "classic" applications function properly under this environment, but compatibility is only assured if the software was written to be unaware of the actual hardware, and to interact solely with the operating system. The Classic Environment is not available on Intel-based Macintoshes due to the incompatibility of Mac OS 9 with the x86 hardware, and was removed completely on Mac OS X 10.5.

Users of the original Mac OS generally upgraded to Mac OS X, but many criticized it as being more difficult and less user-friendly than the original Mac OS, for the lack of certain features that had not been re-implemented in the new OS, or for being slower on the same hardware (especially older hardware), or other, sometimes serious incompatibilities with the older OS. Because drivers (for printers, scanners, tablets, etc.) written for the older Mac OS are not compatible with Mac OS X, and due to the lack of OS X support for older Apple machines, a significant number of Macintosh users have still continued using the older classic Mac OS. But by 2005, it has been reported that almost all users of systems capable of running Mac OS X are doing so, with only a small percentage still running the classic Mac OS.^{[citation needed]}

In June 2005, Steve Jobs announced at the Worldwide Developers Conference keynote that Apple computers would be transitioning from PowerPC to Intel processors. At the same conference, Jobs announced Developer Transition Kits that included beta versions of Apple software including Mac OS X that developers could use to test their applications as they ported them to run on Intel-powered Macs. In January 2006, Apple released the first Macintosh computers with Intel processors, an iMac and the MacBook Pro, and in February 2006, Apple released a Mac mini with an Intel Core Solo and Duo processor. On May 16, 2006, Apple released the MacBook, before completing the Intel transition on August 7 with the Mac Pro. To ease the transition for early buyers of the new machines, Intel-based Macs include an emulation technology called Rosetta, which allows them to run (at reduced speed) pre-existing Mac OS X native application software which was compiled only for PowerPC-based Macintoshes.

Robotics

Robotics Portal

Robotics is the science and technology of robots, their design, manufacture, and application.^[1] Robotics requires a working knowledge of electronics, mechanics and software, and is usually accompanied by a large working knowledge of many subjects.^[2] A person working in the field is a roboticist.

Although the appearance and capabilities of robots vary vastly, all robots share the features of a mechanical, movable structure under some form of autonomous control. The structure of a robot is usually mostly mechanical and can be called a kinematic chain (its functionality being akin to the skeleton of the human body). The chain is formed of links (its bones), actuators (its muscles) and joints which can allow one or more degrees of freedom. Most contemporary robots use open serial chains in which each link connects the one before to the one after it. These robots are called serial robots and often resemble the human arm. Some robots, such as the Stewart platform, use closed parallel kinematic chains. Other structures, such as those that mimic the mechanical structure of humans, various animals and insects, are comparatively rare. However, the development and use of such structures in robots is an active area of research (e.g. biomechanics). Robots used as manipulators have an end effector mounted on the last link. This end effector can be anything from a welding device to a mechanical hand used to manipulate the environment.

Etymology

The word robotics was first used in print by Isaac Asimov, in his science fiction short story "Runaround", published in March 1942 in Astounding Science Fiction.^[3] While it was based on the word "robot" coined by science fiction author Karel Čapek, Asimov was unaware that he was coining a new term. The design of electrical devices is called electronics, so the design of robots is called robotics.^[4] Before the coining of the term, however, there was interest in ideas similar to robotics (namely automata and androids) dating as far back as the 8th or 7th century BC. In the Iliad, the god Hephaestus made talking handmaidens out of gold.^[5] Archytas of Tarentum is credited with creating a mechanical Pigeon in 400 BC.^[6] Robots are used in industrial, military, exploration, home making, and academic and research applications.^[7]

Components of robots

Actuation

The actuators are the 'muscles' of a robot; the parts which convert stored energy into movement. By far the most popular actuators are electric motors, but there are many others, some of which are powered by electricity, while others use chemicals, or compressed air.

• Motors: By far the vast majority of robots use electric motors, of which there are several kinds. DC motors, which are familiar to many people, spin rapidly when an electric current is passed through them. They will spin backwards if the current is made to flow in the other direction.
• Stepper Motors: As the name suggests, stepper motors do not spin freely like DC motors, they rotate in steps of a few degrees at a time, under the command of a controller. This makes them easier to control, as the controller knows exactly how far they have rotated, without having to use a sensor. Therefore they are used on many robots and CNC machining centres.
• Piezo Motors: A recent alternative to DC motors are piezo motors, also known as ultrasonic motors. These work on a fundamentally different principle, whereby tiny piezoceramic legs, vibrating many thousands of times per second, walk the motor round in a circle or a straight line.^[8] The advantages of these motors are incredible nanometre resolution, speed and available force for their size.^[9] These motors are already available commercially, and being used on some robots.^[10][11]
• Air Muscles: The air muscle is a simple yet powerful device for providing a pulling force. When inflated with compressed air, it contracts by up to 40% of its original length. The key to its behaviour is the braiding visible around the outside, which forces the muscle to be either long and thin, or short and fat. Since it behaves in a very similar way to a biological muscle, it can be used to construct robots with a similar muscle/skeleton system to an animal.^[12] For example, the Shadow robot hand uses 40 air muscles to power its 24 joints.
• Electroactive Polymers: These are a class of plastics which change shape in response to electrical stimulation.^[13] They can be designed so that they bend, stretch or contract, but so far there are no EAPs suitable for commercial robots, as they tend to have low efficiency or are not robust.^[14] Indeed, all of the entrants in a recent competition to build EAP powered arm wrestling robots, were beaten by a 17 year old girl.^[15] However, they are expected to improve in the future, where they may be useful for microrobotic applications.^[16]

• Elastic nanotubes are a promising, early-stage experimental technology. The absence of defects in nanotubes enables these filaments to deform elastically by several percent, with energy storage levels of perhaps 10J per cu. cm for metal nanotubes. Human biceps could be replaced with an 8mm diameter wire of this material. Such compact "muscle" might allow future robots to outrun and outjump humans. ^[17]

Manipulation

Robots which must work in the real world require some way to manipulate objects; pick up, modify, destroy or otherwise have an effect. Thus the 'hands' of a robot are often referred to as end effectors^[18], while the arm is referred to as a manipulator.^[19] Most robot arms have replacable effectors, each allowing them to perform some small range of tasks. Some have a fixed manipulator which cannot be replaced, while a few have one very general purpose manipulator, for example a humanoid hand.

• Grippers: A common effector is the gripper. In its simplest manifestation it consists of just two fingers which can open and close to pick up and let go of a range of small objects. See End effectors [1].
• Vacuum Grippers: Pick and place robots for electronic components and for large objects like car windscreens, will often use very simple vacuum grippers. These are very simple astrictive devices, but can hold very large loads provided the prehension surface is smooth enough to ensure suction.
• General purpose effectors: Some advanced robots are beginning to use fully humanoid hands, like the Shadow Hand (right), or the Schunk hand.^[20] These highly dexterous manipulators, with as many as 20 degrees of freedom and hundreds of tactile sensors^[21] can be difficult to control. The computer must consider a great deal of information, and decide on the best way to manipulate an object from many possibilities.

For the definitive guide to all forms of robot endeffectors, their design and usage consult the book "Robot Grippers" ^[22].

Locomotion

Rolling Robots

For simplicity, most mobile robots have four wheels. However, some researchers have tried to create more complex wheeled robots, with only one or two wheels.

• Two-wheeled balancing: While the Segway is not commonly thought of as a robot, it can be thought of as a component of a robot. Several real robots do use a similar dynamic balancing algorithm, and NASA's Robonaut has been mounted on a Segway.^[23]
• Ballbot: Carnegie Mellon University researchers have developed a new type of mobile robot that balances on a ball instead of legs or wheels. "Ballbot" is a self-contained, battery-operated, omnidirectional robot that balances dynamically on a single urethane-coated metal sphere. It weighs 95 pounds and is the approximate height and width of a person. Because of its long, thin shape and ability to maneuver in tight spaces, it has the potential to function better than current robots can in environments with people.^[24]
• Track Robot: Another type of rolling robot is one that has tracks, like NASA's Urban Robot, Urbie. ^[25]

Walking Robots

Walking is a difficult and dynamic problem to solve. Several robots have been made which can walk reliably on two legs, however none have yet been made which are as robust as a human. Typically, these robots can walk well on flat floors, and can occasionally walk up stairs. None can walk over rocky, uneven terrain. Some of the methods which have been tried are:

• Zero Moment Point (ZMP) Technique: is the algorithm used by robots such as Honda's ASIMO. The robot's onboard computer tries to keep the total inertial forces (the combination of earth's gravity and the acceleration and deceleration of walking), exactly opposed by the floor reaction force (the force of the floor pushing back on the robot's foot). In this way, the two forces cancel out, leaving no moment (force causing the robot to rotate and fall over).^[26] However, this is not exactly how a human walks, and the difference is quite apparent to human observers, some of whom have pointed out that ASIMO walks as if it needs the lavatory.^[27][28][29] ASIMO's walking algorithm is not static, and some dynamic balancing is used (See below). However, it still requires a smooth surface to walk on.
• Hopping: Several robots, built in the 1980s by Marc Raibert at the MIT Leg Laboratory, successfully demonstrated very dynamic walking. Initially, a robot with only one leg, and a very small foot, could stay upright simply by hopping. The movement is the same as that of a person on a pogo stick. As the robot falls to one side, it would jump slightly in that direction, in order to catch itself.^[30] Soon, the algorithm was generalised to two and four legs. A bipedal robot was demonstrated running and even performing somersaults.^[31] A quadruped was also demonstrated which could trot, run, pace and bound.^[32] For a full list of these robots, see the MIT Leg Lab Robots page.
• Dynamic Balancing: A more advanced way for a robot to walk is by using a dynamic balancing algorithm, which is potentially more robust than the Zero Moment Point technique, as it constantly monitors the robot's motion, and places the feet in order to main stability.^[33] This technique was recently demonstrated by Anybots' Dexter Robot,^[34] which is so stable, it can even jump.^[35]
• Passive Dynamics: Perhaps the most promising approach being taken is to use the momentum of swinging limbs for greater efficiency. It has been shown that totally unpowered humanoid mechanisms can walk down a gentle slope, using only gravity to propel themselves. Using this technique, a robot need only supply a small amount of motor power to walk along a flat surface or a little more to walk up a hill. This technique promises to make walking robots at least ten times more efficient than ZMP walkers, like ASIMO.^[36][37]