Code: The Hidden Language of Computer Hardware and Software

by Petzold Charles

Everyone knows that flashlights were invented to let kids read books under the bed covers;

Almost everyone knows a little Morse code. Three dots, three dashes, and three dots represent SOS, the international distress signal. SOS isn’t an abbreviation for anything—it’s simply an easy-to-remember Morse code sequence.

The earth is to electrons as an ocean is to drops of water. The earth is a virtually limitless source of electrons and also a giant sink for electrons.

The historic day was May 24, 1844, when a telegraph line rigged between Washington, D.C., and Baltimore, Maryland, successfully carried the biblical message: “What hath God wrought!”

The relay is a remarkable device. It’s a switch, surely, but a switch that’s turned on and off not by human hands but by a current. You could do amazing things with such devices. You could actually assemble much of a computer with them.

It’s no coincidence that the word digit can refer to fingers or toes as well as numbers or that the words five and fist have similar roots.

An Investigation of the Laws of Thought on Which Are Founded the Mathematical Theories of Logic and Probabilities (1854),

Boole died in 1864 at the age of 49 after hurrying to class in the rain and contracting pneumonia.

Although this circuit contains nothing that wasn’t invented in the nineteenth century, nobody in that century ever realized that Boolean expressions could be directly realized in electrical circuits. This equivalence wasn’t discovered until the 1930s, most notably by Claude Elwood Shannon (born 1916), whose famous 1938 M.I.T. master’s thesis was entitled “A Symbolic Analysis of Relay and Switching Circuits.” (Ten years later, Shannon’s article “The Mathematical Theory of Communication” was the first publication that used the word bit to mean binary digit.)

switch is closed: Similarly, the lightbulb remains on when the bottom switch is closed:

The human species is often amazingly inventive and industrious but at the same time profoundly lazy.

Few fantasies tickle the human pleasure center more than a vision of relaxing in a hammock watching some newfangled contraption we just built mow the lawn.

Sometimes computer programmers are known as coders, although some might consider this a derogatory term. Such programmers might prefer to be called software engineers.

“We may say that the Analytical Engine weaves algebraical patterns just as the Jacquard-loom weaves flowers and leaves.”

Herman Hollerith also set in motion a long trail of events. In 1896, he founded the Tabulating Machine Company to lease and sell the punch-card equipment. By 1911, with the help of a couple of mergers, it had become the Computing-Tabulating-Recording Company, or C-T-R. By 1915, the president of C-T-R was Thomas J. Watson (1874–1956), who in 1924 changed the name of the company to International Business Machines Corporation, or IBM.

A relay could also fail because of a piece of dirt or paper stuck between the contacts. In one famous incident in 1947, a moth was extracted from a relay in the Harvard Mark II computer. Grace Murray Hopper (1906–1992), who had joined Aiken’s staff in 1944 and who would later become quite famous in the field of computer programming languages, taped the moth to the computer logbook with the note “first actual case of bug being found.”

It wasn’t until the mid-1950s that magnetic core memory was developed. Such memory consisted of large arrays of little magnetized metal rings strung with wires. Each little ring could store a bit of information. Long after core memory had been replaced by other technologies, it was common to hear older programmers refer to the memory that the processor accessed as core.

The transistor didn’t come out of the blue. Eight years earlier, on December 29, 1939, Shockley had written in his notebook, “It has today occurred to me that an amplifier using semiconductors rather than vacuum is in principle possible.” And after that first transistor was demonstrated, many years followed in perfecting it. It wasn’t until 1956 that Shockley, Bardeen, and Brattain were awarded the Nobel Prize in physics “for their researches on semiconductors and their discovery of the transistor effect.”

In 1956, Shockley left Bell Labs to form Shockley Semiconductor Laboratories. He moved to Palo Alto, California, where he had grown up. His was the first such company to locate in that area. In time, other semiconductor and computer companies set up business there, and the area south of San Francisco is now informally known as Silicon Valley.

With the advent of the transistor and the work in semiconductors generally, it seems now possible to envisage electronic equipment in a solid block with no connecting wires. The block may consist of layers of insulating, conducting, rectifying and amplifying materials, the electrical functions being connected directly by cutting out areas of the various layers.

In the history of technology, simultaneous invention is more common than one might suspect. Although Kilby had invented the device six months before Noyce, and Texas Instruments had applied for a patent before Fairchild, Noyce was issued a patent first. Legal battles ensued, and only after a decade were they finally settled to everyone’s satisfaction. Although they never worked together, Kilby and Noyce are today regarded as the coinventors of the integrated circuit, or IC, commonly called the chip.

To quote Robert Noyce, “After you become reconciled to the nanosecond, computer operations are conceptually fairly simple.”

Intel set the initial price of the 8080 at $360, a sly dig at IBM’s System/360, a large mainframe system used by many large corporations that cost millions. (Today you can buy an 8080 chip for $1.95.)

For black and white television, this video signal is quite straightforward and easy to comprehend. (Color gets a bit messier.) Sixty times per second, the signal contains a vertical sync pulse that indicates the beginning of a field. This pulse is 0 volts (ground) for about 400 microseconds. A horizontal sync pulse indicates the beginning of each scan line: The video signal is 0 volts for 5 microseconds 15,750 times per second. Between the horizontal sync pulses, the signal varies from 0.5 volt for black to 2 volts for white, with voltages between 0.5 volt and 2 volts to indicate shades of gray.

Notice that I haven’t mentioned any way to express a very common number that we seem to have forgotten about, namely 0. That’s one of the special cases, which are these: If e equals 0, and f equals 0, the number is 0. Generally, all 32 bits are set to 0 to signify 0. But the sign bit can be 1, in which case the number is interpreted as a negative 0. A negative 0 can indicate a very small number that can’t be represented with the available digits and exponents in single-precision format but which is still less than 0. If e equals 0 and f doesn’t equal 0, the number is valid, but it’s not normalized. The number equals (–1)s x 0.f x 2-127 Notice that the significand has a 0 to the left of the binary point. If e equals 255 and f equals 0, the number is positive or negative infinity, depending on the sign s. If e equals 255 and f doesn’t equal 0, the value is considered to be not a number, which is abbreviated NaN. A NaN could indicate an unknown number or the result of an invalid operation.

You might recall that 10 binary digits are approximately the same as 3 decimal digits. By that I mean that 10 bits set to 1, which is 3FFh in hexadecimal and 1023 in decimal, is approximately equal to 3 decimal digits set to 9, or 999. Or 210 ≈ 103

Programming in machine code is like eating with a toothpick. The bites are so small and the process so laborious that dinner takes forever. Likewise, the bytes of machine code perform the tiniest and simplest of imaginable computing tasks—loading a number from memory into the processor, adding it to another, storing the result back to memory—so that it’s difficult to imagine how they contribute to an entire meal.

“Rather,” wrote physicist Richard Feynman, “computer science is like engineering—it is all about getting something to do something.”

“As We May Think”

The first indication that home computers were going to be much different from their larger and more expensive cousins was probably the application VisiCalc. Designed and programmed by Dan Bricklin (born 1951) and Bob Frankston (born 1949) and introduced in 1979 for the Apple II, VisiCalc used the screen to give the user a two-dimensional view of a spreadsheet. Prior to VisiCalc, a spreadsheet (or worksheet) was a piece of paper with rows and columns generally used for doing series of calculations. VisiCalc replaced the paper with the video display, allowing the user to move around the spreadsheet, enter numbers and formulas, and recalculate everything after a change.

Another early visionary of interactive computing was Douglas Engelbart (born 1925), who read Vannevar Bush’s article "As We May Think” when it was published in 1945 and five years later began a lifetime of work developing new ideas in computer interfaces. In the mid-1960s, while at the Sanford Research Institute, Engelbart completely rethought input devices and came up with a five-pronged keyboard for entering commands (which never caught on) and a smaller device with wheels and a button that he called a mouse. The mouse is now almost universally accepted for moving a pointer around the screen to select on-screen objects.

The length of 74 minutes was chosen so that Beethoven’s Ninth Symphony could fit on one CD.

Code was conceived in 1987. It rattled around in my head for nearly a decade and was finally committed to a Microsoft Word file between January 1996 and July 1999.