thimble printer
thin client
thin server
Thinking Machines Corp. (TMC)
ThinkPad
third-generation language (3GL)
third-party vendors
thread
three-dimensional (3-D)
three-dimensional audio (3-D audio)
three-dimensional video (3-D video)
three-tier client/server
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thimble printer

A thimble printer is a type of strike printer, also known as an impact printer. This type of printer functions similarly to a typewriter. The printer has an ink ribbon positioned in front of the paper. In order to print a character, the printer strikes the ribbon with a solid, but reversed, image of that character. The ink is then transferred to the paper to form the character.

Prior to laser printers, strike printers produced the highest quality print available. Because the paper was struck to produce the image, strike printers worked with carbon paper forms. Many of them were built using rollers to move the paper, again similar to a typewriter. This let them work with forms not designed to feed through a
computer printer via tractor feed.

The most common form of strike printer is a daisy wheel printer, where each letter is positioned as a spoke around a wheel. With a thimble printer, instead of a wheel, characters are facing out and around the rim of a thimble-shaped cup. The cup rotates to position the appropriate character in front of the paper. The once popular NEC Spinwriters, which are no longer made, are an example of thimble printers.

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thin client

In a networked environment, this is a low-cost, centrally managed device that loads its OS (operating system) from the server, runs applications stored on the server, and saves its data to the server. Because most of the processing is performed on the server, the server is often called a fat server.

Often, the thin client is a PC without a hard drive. Thin clients include Windows terminals, Java-based network computers, and a standard LAN (local-area network) terminal. Because the fat server performs the processing, the thin client does not require a lot of speed or memory, so it is typically a fairly low-cost device.

The main advantage of a thin client is that the applications and data are stored on the server so most of the maintenance and upgrades can be performed centrally on the one fat server rather than locally on numerous individual computers. Although incorrect, the term "thin client" is often used as a synonym for the NetPC and the network computer.

The term "thin client" is also used in conjunction with client/ server software applications. Most application programs have three major layers. The top tier is the presentation layer. This layer handles the interface between the computer and the human. For example, it handles getting input from the keyboard or mouse and displaying information to the screen. The middle layer performs the specific action of the software, such as data entry or order processing. In the client/server environment, this tier is often called the business logic layer because it applies the rules that govern business operation to the data stored in the database. The bottom layer
provides any generalized services the other two tiers need. This might include file services, print services, or database services. In a client/server application, this layer is usually a database and is commonly called the data layer.

These three layers can be incorporated into a single application to run on a single computer or spread across multiple applications to run on multiple computers. An application that has little or no business logic is said to be a thin client. Likewise, an application that has a lot of business logic is said to be a fat client.

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Thinking Machines Corp. (TMC)

The now-defunct TMC was founded in 1983 to build supercomputers devoted to AI (artificial intelligence). TMC recruited the top researchers in the AI field to help design its computers.

In April 1986, TMC announced its first product, the CM-1 (Connection Machine Model 1). The CM-1 departed from the conventional computer architecture of its day. Rather than having a single, very powerful processor to handle all the calculations, the CM-1 was a massively parallel supercomputer that supported a maximum of 65,536 single bit processors arranged in a hypercube. Each of these processors could run simultaneously, similar to the cells in a human brain all working at the same time. This allowed complex problems to be broken apart and each part worked on individually so a solution could be found faster. Because its corporate focus was on AI, that approach made sense for TMC.

Each 1 bit processor in the CM-1 had 4KB of memory. The CM-1 was capable of 1,000 MIPS (millions of instructions per second). The CM-1 needed a parallel processing programming language, and the language that TMC developed was a hybrid of the programming language Lisp (list processing) called *Lisp (pronounced Star Lisp).

A year later, in April 1987, TMC announced the next version of the Connection Machine, the CM-2. The CM-2 was capable of 5 gigaflops (1 billion floating-point operations per second) for matrix multiplication, and it had a 10GB storage system called the DataVault. The CM-2 added support for two additional parallel processing programming languages, C* (pronounced Cee Star) and CM-FORTRAN.

After the release of the CM-1 supercomputer and before the release of the CM-2 supercomputer, TMC experienced a major shift in its focus. Rather than targeting AI, as the CM-1 had, the CM-2 was targeted at scientific research and complex commercial application. This can be seen in the choice of programming languages. The CM-1 ran *Lisp exclusively, and Lisp was the language of AI. The CM-2 added support for parallel processing hybrids of the commercial language C and the scientific language FORTRAN.

This transition was extremely significant. It involved a change in the company structure, changes in its product line, and a shift in its target customers. However, the transition was absolutely necessary. TMC had realized there was not an established market for AI hardware large enough to support the company. It also realized that it had greatly underestimated the difficulty of the AI problems it was tackling.

In November 1991, TMC announced its final hardware product, the CM-5 (there was no CM-3 or CM-4). The computer had a completely redesigned internal communications architecture. Additionally, it had as many as 1,024 sparc (scalable performance architecture) microprocessors connected in a fat tree topology. With all 1,024 processors installed, similar to the one installed at Los Alamos, the theoretical peak performance for the machine was just more than 163 gigaflops.

At its height, TMC machines were installed at 70 different locations worldwide, and TMC produced four of the world's 10 most powerful supercomputers. One of the CM-2 computers is included in the Smithsonian Institution's collection in the Museum of American History.

In 1994, TMC filed for Chapter 11 bankruptcy, from which it emerged in 1996 when TMC left the hardware industry and turned itself into a company focused exclusively on the data-mining software market. Its first product was Darwin, a high-end data-mining software package. Darwin had been originally released for the CM-5 in 1994. From 1996 to 1999, TMC ported Darwin to additional platforms, improved the user interface, and improved and extended the algorithms built into the software.

In 1999, TMC went bankrupt again. This time, however, it would not emerge. Oracle purchased most of the assets of TMC, including the Darwin software and the http://www.think.com Web site. All of the Darwin engineers went to work for Oracle, and Oracle has since incorporated Darwin into its 9i database software. Oracle turned the Web site into a global learning community that connects students and teachers on the Web.

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ThinkPad The ThinkPad is a popular notebook computer from IBM.

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thin server

A thin server is a specialized, network-based computer with a built-in OS (operating system). A thin server is inexpensive and has an appliance-like design. It performs a single function or several related and specialized functions, such as serving up Web pages, sharing Internet access, acting as a firewall, or running a database.

In a typical network environment, the server is an expensive and complex computer for serving up data and applications to client machines connected to its network. Multipurpose servers are sometimes called fat servers. These expensive and complex servers are overkill for many applications.

Although a thin server lacks the flexibility of a fat server, it offers two big advantages: low cost and ease of use. It is a closed box that is quick and easy to install. It requires minimal maintenance and can be configured and managed remotely using a Web browser. Thin servers also take up much less space and use less electricity than a fat server.

The concept of a thin server is nothing new. Routers are nothing more than thin servers. Print servers and specialized storage devices that attach to a network are other examples of thin servers that have been in use for many years. Common thin servers include network appliances, Internet appliances, and server appliances.

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third-generation language (3GL) With a 3GL, a compiler translates human-readable instructions into code the computer can understand.

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third-party vendors

In the computer industry, a third-party vendor is a company that sells products that are designed to work with hardware or software from another company. For example, if a Hewlett-Packard laser printer is designed to work with a Gateway computer, HP would be a third-party vendor for Gateway.

It is the third-party vendors who are inventive and innovative and keep the computer industry moving at its rapid pace. The original IBM PC was a hit not because it was the best computer on the market but because businesses wanted it to run Lotus 1-2-3. Lotus 1-2-3 drove the sales of the IBM PC.

This trend has continued throughout the years. Powerful desktop publishing software drove the demand for laser printers, the popularity of MP3 drives the demand for large hard drives, the innovative software available for the PDAs (personal digital assistants) drives demand for those PDAs, and so on.

Third-party vendors are common in the service sector of the computer industry, as well. With services, any service that is outsourced is being handled by a third-party vendor. For example, it is not uncommon for Web commerce sites to outsource their shopping cart and credit card fulfillment to a third party.

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thread A threaded discussion, such as this discussion devoted to SpamCop, lets readers follow the ebbs and flows of the online conversation.

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three-dimensional (3-D)

An object that is described as being 3-D has or appears to have depth of field. In computing, 3-D objects do not necessarily offer three dimensions, but they usually have greater depth and richer output. When 3-D images are made interactive, a virtual reality is created. A special plug-in, an instruction that adds to the functionality of a program without changing the program's base code, is often needed for your Web browser to handle 3-D graphics.

Creating a 3-D image is a three-phase process. In the first phase, which is called tessellation, models of the objects are created and made into individual polygons. In the geometry phase, those polygons are transformed and special effects, such as lighting, are applied to the object. In the final rendering phase, the newly transformed images are made into 3-D objects, with great attention being paid to small details.

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three-dimensional audio (3-D audio)

Audio that seems to come from all directions, including above and below the listener, is known as 3-D audio. Most of today's computers and stereos only reproduce sound in 2-D (right or left and near or far). Although audio systems such as Surround Sound give the impression of hearing sound all around you (instead of right in front of you, where the speakers are), they can't reproduce the up-down effect of 3-D audio.

Besides the obvious benefits of richer, fuller-sounding music and movie soundtracks, 3-D audio may also prove useful in fields, such as teleconferencing, where it can be difficult to keep track of all the participants' voices. 3-D audio is especially popular on PCs with speakers placed closely together, which offer poor channel separation. Placing a device, which analyzes the sound coming from the speakers and sends feedback back to the sound system, in a room that houses many speakers produces 3-D audio.

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three-dimensional video (3-D video)

3-D video adds the perception of depth to computer screens, which generally only provide cues as to left-right and up-down, not near-far. 3-D graphics are also capable of showing shadows and layers where one object is perceived as partially obscuring another object behind it, with the amount of obscurity changing depending on your position relative to the objects.

Games that feature travel through maze-like hallways have spurred development of 3-D graphics and video. Rendering 3-D images on computers was once slow, but today's faster computers and graphics accelerator cards can render images fast enough to be used in live-action games, and the quality of the 3-D renderings keeps improving. Video cards with 3-D capabilities offer better graphics by using fast, built-in hardware to do certain computing tasks rather than software to perform some graphics calculations. The result is a more fluid image with enhanced colors.

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three-tier client/server The layers of a three-tier application include the presentation layer, the business logic layer, and the data layer. The three layers are separated, but they still communicate with each other.

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thumbnail These Microsoft Word thumbnails show you small mockups of how the pages will look when they are printed. Their small size lets you concentrate on the big picture.

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