一本被盛赞的计算机科学入门书籍，在不同的地方看到推荐，大概有3次以上，根据介绍，推测和 Crash Course 的 CS 课程差不多有趣。
- a big apple
- something blue
- apple tree
- 非谓语动词在名词后修饰：something to eat/the man standing by the window
Preface to the Paperback Edition
I also hope that you might recognize the computer to be one of the crowning achievements of twentieth century technology and appreeciate it as a beautiful thing in itself without metaphors and similes getting in the way.
The further back in time you go, the simpler the technologies become.
- 译者翻译：学习技术发展史的重要意义在于 追溯的历史越久远，技术的脉络就越清晰。
Chapter 1. Best Friends
- the code you invented VS Morse code
- You could say Endlish vocabulary is a type of code
- Just as Morse code provides a good introduction to the nature of codes, the telegraph provides a good introduction to the hardware of the computer.
Chapter 2. Codes and Combinations
- Morse code is said to be a binary(literally meaning two by two)code because the components of the code consist of only two things--a dot and a dash.
Chapter 3. Braille and Binary Codes
- Dissect Braille code and see how it works.
- We just want some insight into the nature of codes.
- shift codes
- escape codes
Chapter 4. Anatomy of a Flashlight
- all matter——the stuff that we can see and feel(usually)——is made up of extremely small things called atoms.
- Every atom is composed of three types of particles: neutrons, protons, and eletrons.
- 原子：电子 + 原子核（中子 + 质子）
Chapter 5. Seeing Around Corners
- You're twelve years old, your second-best friend lives in the house next door to yours.
Chapter 6. Telegraphs and Relays
- In the early 1800s, you could communicate instantly and you could communicate over long distances, but you couldn't do both at the same time.
- The electromagnet is the foundation of the telegraph. Turning the switch on and off at one end causes the electromagnet to do something at the other end.
The historic day was May 24, 1844.(the first telegraph used the Morse)
- the practical lightbulb wouldn't be invented until 1879.
- the relay is a switch, but a switch that's turned on and off not by human hands but by a current.
Chapter 7. Our Ten Digits
- Numbers are certainly the most abstract codes we deal with on a regular basis.
- Much of this chapter and the next will be devoted to persuading ourselves that this many(3) apples can also be indicated by writing 11.
- Roman numerals and Indo-Arbic
0, The lowly zero is without a doubt one of the most important inventions in the history of numbers and mathematics.
- It supports positional notation because it allows differentiation of 25 from 205 and 250.
- The zero also eases many mathematial operations that are awkward in nonpositiona systems, particularly multiplication and division.
Each position corresponds to a power of ten.
- we don't need a special symbol for ten because we set the 1 in a different position and we use the 0 as a placeholder.
Chapter 8. Alternatives to Ten
When you're working with number systems other than decimal, you can avoid some confusion if you pronounce a number like 10 as one zero.
- Similarly, 13 is pronounced one three and 20 is pronounced two zero.
- To really avoid confusion, we can say two zero base eight or two zero octal.
Anytime we have a binary number composed of a 1 followed by all zeros, that number is a power of two.
- The power is the same as the number of zeros in the binary number.
bit: binary digit
- Around 1948, Tukey decided to coin a new shorter word to replace the unwield five syllables of binary digit.
- He considered bigit and binit but settled instead on the short, simple, elegant, and perfectly lovely word bit.
Chapter 9. Bit by Bit By bit
The thing about the bit is that it conveys very little information.
- A bit of information is the tiniest amount of information possible. Anythin less than a bit is no information at all.
- If you can't express something in words, pictures, or sounds, you're not going to be able to encode the information in bits.
As we shall see later in this book, bits can represent words, pictures, sounds, music, and movies as well as product codes, film speeds, movie ratings, an invasion of the British army, and the intentions of one's beloved.
- but most fundamentally, bits are numbers.
- All that needs to be done when bits represent other information is to count the number of possibilities.
- This determines the number of bits that are needed so that each possibility can be assigned a number.
Chapter 10. Logic and Switches
- The + symbol in Boolean algebra means a union of two classes.
- The x symbol in Boolean algebra means an intersection of two classes.
To avoid confusion between conventional algebra and Boolean algebra, sometimes the symbols U and ∩ are used for union and intersection instead of + and x.
- But part of Boole's liberating influence on mathematics was to make the use of familiar operators more abstract, so I've decided to stick with his decision not to intorduce new symbol into his algebra.
- class and set
- we can use the symbol and or instead of x +, the not means 1-.
- This simple circuit to be wired in series is actually performing an AND operation in Boolean algebra.
- The circuit to be connected in parallel is performing an OR operation.
Chapter 11. Gates(Not Bill)
- Logic gates perform simple tasks in logic by blocking or letting through the flow of electrical current.
Although this circuit contains nothing that wasn't inented 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 Shanno(born 1916), whose famous 1938 M.I.T.master's thesis was entitled "A Symbolic Analysis of Relay and Switching Cricuits."
- Ten years later, Shannon's article "The Mathematical Theory of Communication" was the first publication that used the word bit to mean binary digit.
- control panel
- The swithches are an input device in computer terminology.
- Input is information that controls how a circuit behaves.
- Relays have an advantage over switches in that relays can be switched on and off by other relays rather than by fingers.
- Connecting relays is the key to build logic gates.
- AND Gate: To avoid excessive drawing, electrical engineers have a special symbol for an AND gate. That symbol looks like this: Input - - ——output
- OR Gate: It's somewhat similar to the symbol for the AND gate except that the input side is rounded, much like the O in OR.
Inverter: A single relay wired in this way is called an inverter, because it inverts 0 to 1 and vice versa.
- Notice the little circle mean that the signals are inverted at that point.
- Buffer: The output of the buffer is the same as the input.
- If you look at the two inputs to each AND gate to see where they're coming from and try to ignore where they're also going, you'll see that the circuit works.
- There are two relays in every AND gate and OR gate, and one relay for each inverter.
- NOR Gate: This behavior is precisely the opposite of what happens with the OR gate. It's called NOT OR, more concisely, NOR.
- NOT AND Gate: NAND
- So now we have four logic gates and the inverter. Completing this array of tools is just a regular old relay.
- De Morgan's Laws: <Formal Logic>.1847
Chapter 12. A Binary Adding Machine
- If we can build something that adds, we're well on our way to building something that uses addition to also subtract, multiply, divide, calculate mortgage payments, guide rockets to Mars, play chess, and foul up our phone bills.
- There's no way that anyone could make sense of 144 relays wired together in strange ways.
- XOR Gate: 1+1 = 0 这个可以用来表示加法进位后的情况
- Half Adder（半加器）：它将两个二进制数相加，得出一个加法位和一个进位位
- Full Adder（全加器）：两个二进制数相加，还有加上前一列的一个进位数字即3个数字相加
- Ripple carry: 这一章可以进行更深一层的原理巩固和动手制作