2019-2020-1 semester 20,192,419 "Introduction to cyberspace security professionals," summed up the first week of learning (reading notes)

And binary value art systems

2.1 Digital and Computing

Digital: a unit of abstract mathematical systems, obey the laws of arithmetic.
NATURAL: 0 obtained by repeating any number added to the 1 or 0.
Negative: less than the number of 0, is the number obtained with a negative sign in front of the corresponding positive number
Negative natural number, natural number or 0: integer
Rational: Business integer or two integers. (Except not including the number 0)

2.2 positional notation
Base: basic value art systems, the digital sum value of the predetermined bit positions used in this system.

Positional notation number is prepared

Positional notation: An expression digital system, arranged in order digit, each digit has a bit value of the digital sum value is the product and the position of each digit and.

Above the middle of the crossbar abacus bead count indicates 5 units, the following represents a unit of counting beads

2.2.1 binary, octal and hexadecimal

Counting system base 16 in the following 16 numbers: 1,2,3,4,5,6,7,8,9
, A, B, C, D, E and F

Any counting system is smaller than the maximum number of the base 1. The use of any radix base value, only; two numbers. In the leftmost 0, 1 0 the left, this figure represents a group value itself.

2.2.2 Other numeration system operation

Binary adder
as: 101110 + 11011 = 1001001

2.2.3 a power of 2 as the base number system

Converting the binary number into octal, binary starts from the rightmost digit, a set of three digits each, to each digital conversion to the corresponding octal number.

2.2.4 converted to decimal number system other numbers

While (quotient is not zero)

new base in addition to the decimal number with

the remainder as the next digit to the left of the answer

instead of decimal numbers with this business

all information is represented by a binary value, because each computer is stored as only high electricity level and a low level of both signals. Since the state of each memory bit is only one of the two, so use the binary logical.

Each memory cell is called a binary digit (or bit bit). The collection of bits that together make bytes (byte), byte together constitute a word. Digit is called word length computer.

Data Representation

3.1 Data and Computer

Data is a basic value or the fact that, while the information mode is somehow able to effectively solve the problem of tissue or processed data. Data is not organized, the lack of context. Information can help us answer the question. Data can be divided into two categories: continuous (analog) and discrete (digital)

Multimedia: several different media types
Data compression: reduce the storage space required piece of data.
Bandwidth: maximum transferred from one location to another location of bits or bytes within a fixed time.
Compression ratio: size of data after compression by dividing the value of the original data size
Lossless compression: compression without losing digital information technology.
Lossy compression: lose data compression technology.

Data representing two ways, i.e., simulation and digital methods. Analog data is a continuous representation, a virtual reality information it represents. Digital data is a discrete representation, the division became a separate information element. (Mercury is an analog device)
analog data correspond exactly to the world around us continuous unlimited. Therefore, the computer can not handle analog data. We need to digital data, the information is divided into segments and each segment separately represented.
Digital: The information is divided into discrete fragments
why modern computers use binary? Because if the device storage and management of data need only represent one of two values, then the cost is much smaller, but also more reliable

PCM: digital signal jump between only two extremes.
Re-timing: too much signal degradation before it is reset to the original state behavior.
n-bit binary numbers can represent 2 ⁿ states, it may be formed as n-bit digital 2 ⁿ combinations of 0 and 1. Please note that whenever an increase in the number of bits available, the number of states will be represented twice

3.2.1 negative representation

Notation consistent values: A symbol classification (positive or negative) number belongs, represents the value of the digital representation of the magnitude of the number.
Signed integer execution of addition and subtraction operations may be described as a certain number of units moved in one direction or the other direction. And two required two numbers, i.e. to find a first scale, then the mobile unit number indicated by the direction indicated by the second number of symbols. Like the embodiment subtraction, i.e. the specified number line in FIG moved along the direction indicated by symbol unit.
If only a quantitative value, it can be half of the number represents a positive number, and the other half represent negative numbers, symbols, determined by the value of the genus. For example, assume that the maximum can be represented in decimal 99, it can be a positive number from 1 to 49 with 1 to 49 50 to 99 -50 to -1 represent a negative number.
Calculating a negative representation
Negative ( the I ) = 10 ^k -I, wherein k is the number of digits. This is called negative decimal complement representation.
Decimal Complement: negative one kind of representation, using negative I k-th power minus 10 I FIG.
* The leftmost digit binary complement representation of this number is negative or positive. If the left is "0", then that figure is positive; if it is "1", then that this number is negative.
Overflow: the number of bits reserved to save any results condition value calculated.

3.2.2 Real notation
We called the real value of non-integer value.
Decimal point: numeration system, to a real number into an integer part and fractional part of the point.
Floating-point representation: a sign marked, real mantissa and exponent representation.
Binary floating-point values are defined:
Symbol mantissa × 2 × ^exp
to convert an integer to a decimal number from another system, in addition to the need to use a new base number, the remainder is a digital result to the left of the dividend is the new supplier, the whole process until quotient is zero terminated. Converting the fractional part of the operation but not with a new base in addition to this number, but take it with a new base. Carry-less multiplication will be the next digit to the right answer, the fractional part of the multiplication result will be the new multiplicand, the whole process until the fractional part of the multiplication result is 0 off.
Another scientific notation floating point representation.

Text representation

Documentation is a continuous (analog) entities, independent character is discrete elements, which is what we want to express and stored in computer memory. A representation common method is to list all the characters of the character, and then given a binary string for each character.
Character set and character represent just a list of their code. Which uses the ASCII character set and Unicode character sets.

3.3.1ASCII character set

ASCII character set is the abbreviation for United States information exchange standards code. ASCII 7 bits initially set to represent each character, can represent 128 different characters. The eighth bit of each character was originally used as a parity bit, helping to ensure correct data transmission. After, ASCII representation of each character by eight. The official version is that the name of eight Latin-1 extended ASCII character set.

3.3.2Unicode character set

Unicode character set with a more powerful international influence, it is a convenient place to ASCII character set as a subset. (Which, Unicode character sets 345F codes from Chinese, Japanese, Korean)

3.3.3 Text Compression
Three texts compression type
Keyword coding
Run length encoding
Huffman coding

Keyword coding

Keywords encoding is a fairly straightforward text compression method, which replaces the single character used words .
* Limitations: 1 is used for character encoding of the keyword can not appear in the original text. For example, if the original paragraph with "$", and that this will be the sign of the word conflict. 2. The word with the different, so want The encoding, it is necessary to use another symbol, or to use a more complex replacement mode. 3. Finally, do not like this word coded "a", because it was just a character.

Run length encoding

Sometimes referred to as run length encoding iterative encoding
e.g., the following seven characters A configuration:. AAAAAAA
if! As a sign of character, this string can be encoded as:! A7

Run length encoding: replace their repeated number of times a series of repeated characters.

Huffman coding
Huffman coding: The character variable-length binary string, so that characters having a common short code.

3.4 audio data representation

A stereo system by sending electrical signals to a speaker to produce sound. This signal is an analog representation of sound waves
digitized this signal, it is necessary to periodically measure the voltage signal, and records the appropriate value, called the sampling process.
Vinyl is an analog representation of sound waves. On the other hand, compact disc (CD) to store the digitized audio information.

3.4.1 Audio Format

WAV, AU, AIFF, VQF and MP3. At present, the dominant format in the compressed audio data is MP3.

3.4.2MP3 audio formats

MP3 is an abbreviation of MPEG-2 audio layer3, MP3 format uses two kinds of lossless compression and lossy compression methods.

3.5.1 Color notation

These photoreceptors are classified corresponding to red, green and blue colors.
Universal RGB color values represented. This is actually three numbers, indicating the relative share of each of the primary colors.
Color depth is the amount of data used to represent the color, usually represented by the number of bits to represent a color depth of color. Enhanced color refers to the color depth of 16-bit color, the RGB value of each digit is represented by 5, and the remaining one is sometimes used to refer to transparency. True color refers to a color depth of 24-bit color.

3.5.2 Digital Image and Graphics
Pixels: isolated dots used to represent the image, the representative image element.
Resolution: isolated dots used to represent the image, the representative image element.
Raster graphics formats: format-by-pixel image information is stored.
GIF files are best used for graphics and images with less color, therefore, he is the preferred format to store the lines of the image. Store photos in JPEG format is seen as the preferred format color images. It uses compressed mode is quite complex, effectively reducing the generation of the file size. PN normally closed better image compression GIF images, a wider color depth provided simultaneously. But it does not support animation.

3.5.3 Vector graphic representation
Unlike raster graphics vector graphics format, as the color-imparting pixels, but with the described geometry and the line segment image.
Vector Graphics: representation of the image and the line segment geometry.
Vector graphics are suitable for line art and cartoon drawing. The network's most popular vector graphics format is Flash . A new SVG vector format under development, which is represented by a plain text. Upon completion of the SVG format, vector graphics may become a popular method of imaging network.

3.6 video representation

Video codec
It represents the codec compressor / decompressor. Video codec method of reducing the size of the film refers to the film can be played on a computer or network. Almost all video codec lossy compression are used, to minimize the amount of data associated with the video.
Two video compression codec used, i.e. time compression, and space compression .
Time Compression: Compression techniques movie based on the difference between successive frames.
Space compression: Compression technology is based on the movie still image compression technology.
Today's popular video codecs have Sorenson, Cinepak, MPEG and Real Video.