In darkest London, Tom Adair follows the clues encrypted in the Da Vinci Code.

'Researching this, I often felt we should be in a federal witness protection program," says Brian Hicks, a Blue Badge guide and sometime winner of London Tourist Board's guide of the year. He has created "Mysterious London and The Da Vinci Code", a tourist trail that takes in the Houses of Parliament, Big Ben and Westminster Abbey, with a ride on London's Underground for good measure.

The route retraces the hokum of Dan Brown's best-selling fiction in London, following in the footsteps of Robert Langdon and Sophie Neveu, the heroes played by Tom Hanks and Audrey Tautou in the spin-off movie. It also doubles as a riveting dig through the entrails of mediaeval Christian England.

Today, there are 10 on the tour: two Australians, three Americans, two Israelis, a Bulgarian, and a woman who says she's "Uranian" (yes, they are even here from Uranus). I had been hoping for rain, for some gothic gloom, a fanfare of thunder, a crack of lightning but, alas, the River Thames glitters gold in the afternoon sun, the wrong kind of alchemy altogether.

At 2pm sharp, Hicks meets us at Temple Tube station and whisks us into the wind-blown shade of Embankment Gardens. "Dan Brown has sold 45 million copies of the book," he says, though the figure is closer to 80 million. "It has been taken very seriously by the Vatican, who appointed the Bishop of Genoa to dispel its various 'lies and misrepresentations'." Hicks's eyebrows rise and he rolls the phrase around his mouth like a connoisseur of ecclesiastical paranoia.

Are we initiated, he asks? Have we seen the movie? Read the novel? It isn't essential but it certainly helps. "The Knights Templar feature hugely in the book. From their inception, they were sponsored by the Pope. Wherever they went, they built circular churches based on the Church of the Holy Sepulchre in Jerusalem." You sense that a circular church is coming up.

"And here it is," he says, leading us through the paved purlieu of riverside courtyards, under the branches of spiked wintry trees, past mantled gaslights and into the deep seclusion of outlandish wealth: the Inns of Court - a den of barristers, of privilege, Aston Martins and Ferraris. And the Templars' church.

"But first," for Hicks cannot resist a colourful digression, "we see before us the Templars' great hall, where Shakespeare acted in Twelfth Night in front of Elizabeth I and where, years later, Robert Louis Stevenson saw names in the stained-glass windows that stirred dark thoughts - of Jekyll and Hyde."

Looming behind the great hall, which survived heavy bombing during World War II, is Temple Church.

"To this very door came Robert and Sophie in the early hours of the morning, along with Leigh Teabing, their accomplice, to find the burial place of a knight. Let's see what they found."

Inside, beneath the leery gaze of gargoyles (featured prominently in the movie to accentuate the menace), are sombre effigies of nine Templars. "Brown suggests there should be a 10th," says Hicks, shaking his head, "[but] there never was."

TempleChurch

As if on cue, the church's organ shatters the silence - something by Bach - like a movie soundtrack, prompting visions of the gripping kidnap scene, the gunfire, Silas the red-eyed albino monk from Opus Dei pressing his knife to Neveu's throat, Teabing bundled into a getaway car. And the attempt to steal the keystone, which holds the map to the Holy Grail.

Hicks's amusement drowns the racket: "Ah, monks with red eyes, dressed in white habits, we see them around here all the time." As the walk winds on between high, bricked chambers, following Langdon and Neveu's escape route, Hicks peppers us with the historical context of the early Christian church and the sacred role of Mary Magdalene, whose sarcophagus, Dan Brown believes, will reveal the final meaning of the Grail itself - Jesus Christ's bloodline and who its inheritors are today.

We absorb odd facts: how the pirate flag, the Jolly Roger, got its name; why Friday the 13th became a cursed date. We are urged to look up and see - on weathervanes, atop archways, on gothic lamps - the Agnus Dei, or lamb of god - the symbol of the Knights Templar. Every detail links to our quest. Minutes later, we spill through a gateway into the traffic of the Strand, a blur of taxis and red double-deckers. Hicks's arms become a flurry, pointing up, to the left and right, then above our heads, to symbols linking the Templars to Freemasonry and across the road to the law courts of the Old Bailey.

"Dan Brown was summoned to Court 61 here, to defend himself," Hicks says. "Accused of plagiarism. The trial judge said The Da Vinci Code was, quote, 'a thumping good read'. So he wasn't biased. Brown won his case."

For another hour, we pursue The Da Vinci Code's narrative, first to the chapel of King's College London, then into Strand Lane, which conceals a link with Charles Dickens's David Copperfield, as a bonus for sleuths of literary London.

Then there's a headlong rush down the stairwell of Temple Tube, where Langdon and Neveu jump the barrier, pacing the platform, keen to race to the nearby sanctum of Westminster Abbey, where the next clue, and its solution, await.

A few minutes later, we're in daylight and under the 4 o'clock chime of Big Ben. Around the corner at Westminster Hall, Hicks points to where "the first traffic lights in the universe were erected back in 1868". We presume he checked all the other planets.

Here, we relive The Da Vinci Code's dramatic denouement in Westminster Abbey - when the keystone spills its secret. And Hicks throws in his own conundrum: how does a 1960s mural by Jean Cocteau in a hidden church off Leicester Square connect with Leonardo Da Vinci? He leaves this question unanswered.

A few minutes later, on my way to solve the puzzle, I find myself checking the street behind me for red-eyed albinos cloaked as monks. Or Tom Hanks. Or possibly Hicks, on his federal witness protection program, loitering with intent. One can't be too careful, after all.

The walking tour, Mysterious London and The Da Vinci Code, is held on Thursdays at 2pm, departing from Temple Tube station (Circle and District lines). The walk costs £7 ($12) for adults and is free for under-15s. Bookings not essential. See londonwalks.com.

Understanding Computers - Part 2 of 5

Introduction to Computers

The Big Picture

A computer system has three main components: hardware, software, and people. The equipment associated with a computer system is called hardware. Software is a set of instructions that tells the hardware what to do. People, however, are the most important component of a computer system - people use the power of the computer for some purpose. In fact, this course will show you that the computer can be a tool for just about anyone from a business person, to an artist, to a housekeeper, to a student - an incredibly powerful and flexible tool.

Software is actually a computer program. To be more specific, a program is a set of step-by-step instructions that directs the computer to do the tasks you want it to do and to produce the results you want. A computer programmer is a person who writes programs. Most of us do not write programs, we use programs written by someone else. This means we are users - people who purchase and use computer software.

Hardware: Meeting the Machine

What is a computer? A six-year-old called a computer "radio, movies, and television combined!" A ten-year-old described a computer as "a television set you can talk to." The ten-year-old's definition is closer but still does not recognize the computer as a machine that has the power to make changes.

A computer is a machine that can be programmed to accept data (input), process it into useful information (output), and store it away (in a secondary storage device) for safekeeping or later reuse. The processing of input to output is directed by the software but performed by the hardware.

To function, a computer system requires four main aspects of data handling: input, processing, output, and storage. The hardware responsible for these four areas operates as follows:

· Input devices accept data in a form that the computer can use; they then send the data to the processing unit.

· The processor, more formally known as the central processing unit (CPU), has the electronic circuitry that manipulates input data into the information people want. The central processing unit executes computer instructions that are specified in the program.

· Output devices show people the processed data-information in a form that they can use.

· Storage usually means secondary storage. Secondary storage consists of devices, such as diskettes, which can store data and programs outside the computer itself. These devices supplement the computer's memory, which, as we will see, can hold data and programs only temporarily.

Your Personal Computer Hardware

Let us look at the hardware in terms of a personal computer. Suppose you want to do word processing on a personal computer, using the hardware shown in Figure 1.

Figure 1: Personal Computer

Word processing software allows you to input data such as an essay, save it, revise and re-save it, and print it whenever you wish. The input device, in this case, is a keyboard, which you use to type in the original essay and any changes you want to make to it. All computers, large and small, must have a central processing unit within the personal computer housing. The central processing unit under the direction of the word processing software accepts the data you input through the keyboard. Processed data from your personal computer is usually output in two forms: on a screen and eventually by a printer. As you key in the essay on the keyboard, it appears on the screen in front of you. After you examine the essay on the screen, make changes, and determine that it is acceptable, you can print the essay on the printer. Your secondary storage device in this case is a diskette, a magnetic medium that stores the essay until it is needed again.

Now we will take a general tour of the hardware needed for input, processing, output, and storage. These same components make up all computer systems, whether small, medium, or large. In this discussion we will try to emphasize the types of hardware you are likely to have seen in your own environment. These topics will be covered in detail in later chapters.

Input: What Goes In

Input is the data that you put into the computer system for processing. Here are some common ways of feeding input data into the system:

· Typing on a keyboard. Computer keyboards operate in much the same way as electric typewriter keyboards. The computer responds to what you enter; that is, it "echoes" what you type by displaying it on the screen in front of you.

· Pointing with a mouse. A mouse is a device that is moved by hand over a flat surface. As the ball on its underside rotates, the mouse movement causes corresponding movement of a pointer on the computer screen. Pressing buttons on the mouse lets you invoke commands.

· Scanning with a flatbed scanner, wand reader or bar code reader (Figure 2).

Figure 2: Flatbed Scanner

· Flatbed scanners act like a copying machine by using light beams to scan a document or picture that is laid upon its glass face. A great way to send pictures through email! Bar scanners, which you have seen in retail stores, use laser beams to read special letters, numbers, or symbols such as the zebra-striped bar codes on many products.

You can input data to a computer in many other interesting ways, including writing, speaking, pointing, or even by just looking at the data. We will examine all these in detail in a later chapter.