More on this book
Community
Kindle Notes & Highlights
A code is useful if it serves a purpose that no other code can.
A code is useful if it serves a purpose that no other code can.
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.
V stands for voltage, but it could also stand for vacuum. Think of the V as an electron vacuum and think of the ground as an ocean of electrons.
No matter what number system we use, whenever we run out of single digits, the first two-digit number is always 10.
the binary number system bridges the gap between arithmetic and electricity.
bit, coined to mean binary digit,
Conveying one of three possibilities requires another lantern. Once that second lantern is present, however, the two bits allows communicating one of four possibilities: 00 = The British aren’t invading tonight. 01 = They’re coming by land. 10 = They’re coming by land. 11 = They’re coming by sea.
any information that can be reduced to a choice among two or more possibilities can be expressed using bits.
If you can’t express something in words, pictures, or sounds, you’re not going to be able to encode the information in bits. Nor would you want to.
The more bits we have, the greater the number of different possibilities we can convey.
The + symbol in Boolean algebra means a union of two classes. A union of two classes is everything in the first class combined with everything in the second class. For example, B + W represents the class of all cats that are either black or white.
The x symbol in Boolean algebra means an intersection of two classes. An intersection of two classes is everything that is in both the first class and the second class.
George Boole never wired such a circuit. He never had the thrill of seeing a Boolean expression realized in switches, wires, and lightbulbs. One obstacle, of course, was that the incandescent lightbulb wasn’t invented until 15 years after Boole’s death.
What might have helped Babbage, we know now, was the realization that perhaps instead of gears and levers to perform calculations, a computer might better be built out of telegraph relays.
Connecting relays is the key to building logic gates.
As an 8-bit quantity, a byte can take on values from 00000000 through 11111111.
In the eighteenth century (and indeed up to the 1940s), a computer was a person who calculated numbers for hire.
The desire to eliminate errors from mathematical tables motivated the work of Charles Babbage (1791–1871), a British mathematician and economist who was almost an exact contemporary of Samuel Morse.
Beginning about 1820, Babbage believed that he could design and build a machine that would automate the process of constructing a table, even to the point of setting up type for printing.
By the time of the 1880 census, information was accumulated on age, sex, and national origin. The data amassed took about seven years to process.
automating the 1890 census was a resounding success. All told, over 62 million cards were processed. They contained twice as much data as was accumulated in the 1880 census, and the data was processed in about one-third the time.
In 1948, the Eckert-Mauchly Computer Corporation (later part of Remington Rand) began work on what would become the first commercially available computer—the Universal Automatic Computer, or UNIVAC.
The transistor inaugurated solid-state electronics, which means that transistors don’t require vacuums and are built from solids, specifically semiconductors and most commonly (these days) silicon. Besides being much smaller than vacuum tubes, transistors require much less power, generate much less heat, and last longer.
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.
Throughout the 1960s, the space program and the arms race fueled the early integrated circuits market.
Probably the most important fact to know about a particular integrated circuit is the propagation time. That’s the time it takes for a change in the inputs to be reflected in the output.
Clock speed is the maximum speed of an oscillator that you can connect to the microprocessor to make it go. Any faster and it might not work right.
Similarly, playing the last song on a cassette tape requires us to fast forward through the whole side of the album. The term for microfilm or tape storage isn’t random access but sequential access.
It’s possible—possibly due to a bug in a program—that the stack will get so big that it will begin to overwrite some code or data needed by a program. This is a problem known as stack overflow.
don’t think about text as formatted into two-dimensional columns on the printed page. Think of text instead as a one-dimensional stream of letters, numbers, and punctuation marks, with perhaps an additional code to indicate the end of one paragraph and the start of another.
Morse code, for example, is a variable-width code: It uses shorter codes for frequently used letters and longer codes for less common ones.
ASCII is a 7-bit code using binary codes 0000000 through 1111111, which are hexadecimal codes 00h through 7Fh.
say the average book has 333 pages, which may be a made-up figure but nicely implies that the average book is about 1 million bytes, or 1 megabyte.
The United States Library of Congress has about 20 million books for a total of 20 trillion characters, or 20 terabytes, of text data.
Unicode is a 16-bit code. Each and every character in Unicode requires 2 bytes. That means that Unicode has character codes ranging from 0000h through FFFFh and can represent 65,536 different characters. That’s enough for all the world’s languages that are likely to be used in computer communication, with room for expansion.
A bus is simply a collection of digital signals that are provided to every board in a computer. These signals fall into four categories:
1. Address 2. Data Input 3. Data Output 4. Control
Memory is like the top of your desk. Anything that’s on your desk you can work with directly. Storage is like a file cabinet.
Floating-point arithmetic is so important to scientific and engineering applications that it’s traditionally been given a very high priority.
compiler, which is the program that converts the statements of your high-level language to machine code.
“computer science is like engineering—it is all about getting something to do something.”
If programming truly were a science, there wouldn’t be so many possible solutions, and incorrect solutions would be more obvious.
Rather than just sending ASCII characters through the wires, TCP/IP-based transmitters divide larger blocks of data into smaller packets, which are sent separately over the transmission line (often a telephone line) and reassembled on the other end.
So it seems that photons, not electrons, will be responsible for delivering much of the information of the future into our homes and offices; they’ll be like faster dots and dashes of Morse code and those careful pulses of blinking light we once used to communicate late-night wisdom to our best friend across the way.
