Insights from Chapter 9
#1
The slide rule, a small but important segment of American industry, was formally laid to rest in Washington, D. C. , on a summer day in 1976. The slide rule had become a martyr to microelectronic progress.
#2
The competition between the slide rule and the calculator was completely one-sided from the beginning. The slide rule was a simple calculator, but it gave only approximate answers. It offered no help at all in solving some of the trickier aspects of calculation.
#3
The slide rule was a simple instrument that was used to calculate logarithms. It was not considered intelligent, but it was a tool that helped men create the first nuclear chain reaction and send rockets to the stratosphere.
#4
The designers of digital machines have designed an addition circuit in such a way that the pattern of pulses representing binary 5 is the only possible combination that can come out when binary 3 and binary 2 are put in. To get that sum, however, the machine must be pushed to its limits.
#5
A computer has many small black millipedes called chips that perform specific functions. The chip inside DIM-I is a TMS 1000C, one of the common microprocessors designed for small calculators. It has four main functions: input, memory, processing, and output.
#6
The processing circuitry of DIM-I, like that in any digital device, has a central set of logic gates called the control unit. This is a sort of central switchboard that busily directs electronic pulses here and there, from input to memory to processor to the display screen.
#7
The speed of light is the speed at which signals travel inside a digital machine. The clock rate for digital machines is usually set at 10 microseconds, or one pulse every hundred thousandth of a second.
#8
The fundamental two-stage instruction cycle is the vital rhythm of the computer’s life. The clock generator regulates the process so that each signal arrives at its destination before the next signal begins its journey through the circuit.
#9
DIM-I is a computer that is programmed to check all the keys on the keyboard seriatim to see if anyone has pushed any of them. It is a digital device, and it races its way through billions of fetch-and-execute cycles every working day, never getting bored or tired.
#10
The control unit at the heart of DIM-I is like the stationmaster at some isolated depot along the main freight line. It knows that four trains come through from the south each day: the 10:00 A. M. from Tulsa, the noon train from Natchez, the 2:00 P. from Texarkana, and the 4:00 P. from Fort Worth.
#11
The control unit of DIM-I sends a signal to its register, which is a group of four transistors that acts as a small memory unit. The signal switches the transistors on and off, which lines up like this: 3.
#12
The control unit of a calculator can’t process the input without first looking up the instructions. It jumps ahead to the memory location that stores the programmed sequence of steps that will display a number in the first digit position on the screen.
#13
The calculator is faster than the eye. It takes only. 005 second for the display to light up after we push the key, when compared to the human finger, which takes two or three tenths of a second between keys.
#14
The most complicated part of any digital device is the circuitry for the arithmetic unit, which performs the calculations. The basic building blocks of the arithmetic circuit are the standard logic gates that Claude Shannon first proposed in 1937.
#15
The complete operation of the simple circuit presented in Figure 8 is shown in a small, simple logic table: a NOT gate that takes in a 1 will send out a 0, and vice versa. To make a mindless machine like DIM-I add two digits and come up with the right answer every time, the circuit designer first draws up the truth table for a two-input addition problem.
#16
The control unit inside DIM-I notices that someone has pushed the = key. It now goes back to its temporary storage registers to find what the previous key clicks were so that it can do the computation.
#17
The addition circuitry has emitted an answer, and the control unit sends a signal to the output circuitry: Get ready to display the answer. The binary pulses flow in; current flows out along selected wires leading to the display. The chosen segments light up, and the binary answer to the problem, 0101, is translated on the screen to its decimal equivalent.