Python Quiz 1 added!

Computers are often referred to as digital devices. The term digital can be used to describe anything that uses binary numbers. Digital data is data that is stored in binary format, and a digital device is any device that works with binary data. Numbers and characters are stored in binary, but computers also work with many other types of digital data.

For example, consider the pictures that you take with your digital camera. These images are composed of tiny dots of color known as pixels. (The term pixel stands for picture element.) Each pixel in an image is converted to a numeric code
that represents the pixel’s color. The numeric code is stored in memory as a binary number.

False; Designed with readability in mind: “Simple is better than complex”

The Python language uses an interpreter, which is a program that both translates and
executes the instructions in a high-level language program. As the interpreter reads
each individual instruction in the program, it converts it to machine language instruc-tions then immediately executes them. This process repeats for every instruction in
the program. This process is illustrated in Figure 1-19. Because interpreters combine
translation and execution, they typically do not create separate machine language
programs.

The answer is False; Powerful for object-oriented prog and dynamic typing; Python incurs overhead costs as the language is interpreted.

A utility program performs a specialized task that enhances the computer’s operation or safeguards data. Examples of utility programs are virus scanners,
file compression programs, and data backup programs.

Programs that make a computer useful for everyday tasks are known as application software. These are the programs that people normally spend most of their time running on their computers. Two commonly used applications are Microsoft Word, a word processing program, and PowerPoint, a presentation program. Some other examples of application software are spreadsheet programs, email programs, web browsers, and game programs.

Hardware is all the physical devices, or components, of which a computer is made.

It is an encoding scheme that uses a set of 128 numeric codes to represent the English letters, various punctuation marks, and other characters. These numeric codes are used to store characters in a computer’s memory. (ASCII stands for the American Standard Code for Information Interchange.)

Assembly language programs cannot be executed by the CPU, however. The CPU only understands machine language, so a special program known as an assembler is used to translate an assembly language program to a machine language program.

The CPU is the most important component in a computer because it is the part of the computer that runs programs.

Python was introduced in the 1990s.

A compiler is a program that translates a high-level language program into a separate machine language program. The machine language program can then be executed any time it is needed.

From Machine Language to Assembly Language
Computers can only execute programs that are written in machine language. A program can have thousands or even millions of binary instructions, and writ-ing such a program would be very tedious and time consuming. Programming in machine
language would also be very difficult, because putting a 0 or a 1 in the wrong place will cause an error.

Although a computer’s CPU only understands machine language, it is impractical for people to write programs in machine language. For this reason, assembly language was created in the early days of computing as an alternative to machine language. Instead of using binary numbers for instructions, assembly language uses short words that are known as mnemonics. For example, in assembly language, the mnemonic add typically means to add numbers, mul typically means to multiply numbers, and mov typically means to move a value to a location in memory. When a programmer uses assembly language to write a program, he or she can write short mnemonics instead of binary numbers.

You can think of main memory as the computer’s work area. This is where the computer
stores a program while the program is running, as well as the data that the program is
working with. For example, suppose you are using a word processing program to write an
essay for one of your classes. While you do this, both the word processing program and the
essay are stored in main memory.
Main memory is commonly known as random-access memory, or RAM. It is called this
because the CPU is able to quickly access data stored at any random location in RAM.
RAM is usually a volatile type of memory that is used only for temporary storage while
a program is running. When the computer is turned off, the contents of RAM are erased.

In most computer systems, bits are tiny electrical components that can hold either a positive or a negative charge. Computer scientists think of a positive charge as a switch in the on position, and a negative charge as a switch in the off position.

A bit can be used in a very limited way to represent numbers. Depending on whether the bit is turned on or off, it can represent one of two different values. In computer systems, a bit that is turned off represents the number 0, and a bit that is turned on represents the number 1. This corresponds perfectly to the binary numbering system. In the binary numbering system (or binary, as it is usually called), all numeric values are written as sequences of 0s
and 1s.

When all of the bits in a byte are set to 0 (turned off), then the value of the byte is 0. When all of the bits in a byte are set to 1 (turned on), then the byte holds the largest value that can be stored in it. The largest value that can be stored in a byte is 1 2 4 8 16  32 64 128 = 255. This limit exists because there are only eight bits in a byte.

The statements that a programmer writes in a high-level language are called source
code, or simply code. Typically, the programmer types a program’s code into a text
editor then saves the code in a file on the computer’s disk. Next, the programmer uses
a compiler to translate the code into a machine language program, or an interpreter
to translate and execute the code. If the code contains a syntax error, however, it can-not be translated. A syntax error is a mistake such as a misspelled keyword, a missing
punctuation character, or the incorrect use of an operator. When this happens, the
compiler or interpreter displays an error message indicating that the program contains
a syntax error. The programmer corrects the error then attempts once again to translate
the program.

Although people commonly violate the syntax rules of their native language when
speaking and writing, other people usually understand what they mean. Unfortunately, compilers and interpreters do not have this ability.

If even a single syntax error appears in a program, the program cannot be compiled or executed.

When an interpreter encounters a syntax error, it stops executing the program.

A computer’s CPU can only understand instructions that are written in
machine language. Because people find it very difficult to write entire
programs in machine language, other programming languages have been
invented.

The binary numbering system can be used to repre-sent only integer numbers, beginning with 0. Negative numbers and real numbers (such as 3.14159) cannot be represented using the simple binary numbering technique we discussed.
Computers are able to store negative numbers and real numbers in memory, but to do so they use encoding schemes along with the binary numbering system.

Negative numbers are encoded using a technique known as two’s complement, and real numbers are encoded in
floating-point notation. You don’t need to know how these encoding schemes work, only that they are used to convert negative numbers and real numbers to binary format.

When a CPU executes the instructions in a program, it is engaged in a process that is known as the fetch-decode-execute cycle. This cycle, which consists of three steps, is repeated for each instruction in the program. The steps are:
1. Fetch. A program is a long sequence of machine language instructions. The first step of the cycle is to fetch, or read, the next instruction from memory into the CPU.
2. Decode. A machine language instruction is a binary number that represents a com-mand that tells the CPU to perform an operation. In this step, the CPU decodes
the instruction that was just fetched from memory, to determine which operation it
should perform.
3. Execute. The last step in the cycle is to execute, or perform, the operation.

A program is a set of instructions that a computer follows to perform a task.

Secondary storage is a type of memory that can hold data for long periods of time, even
when there is no power to the computer. Programs are normally stored in secondary mem-ory and loaded into main memory as needed. Important data, such as word processing
documents, payroll data, and inventory records, is saved to secondary storage as well.

The CPU understands instructions written in a binary machine language.