Info 1120 - 2.3 Digital Data

2.3.1 - 2.3.6 This section explains the basics of how computers work, including their use of the binary number system and the translation of physical signals into digital information. After finishing this section, you should be able to: Describe the binary number system used by computers to process data. Describe how binary numbers can be translated into hexadecimal form. Define bits and bytes. Explain how physical signals are translated into digital information. Describe the most common character encoding standards, including ASCII and Unicode. Describe the most common units of measurement used for storage, throughput, and processing speed.

Decimal System

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A numbering system that uses ten digits, 0 through 9.

Binary System

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A numbering system that uses two digits, 0 and 1.

Important to know: Binary represents physical signals inside the computer, and hex is an easy way for humans to represent binary numbers

Hexadecimal System

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A numbering system that uses sixteen digits, 0 through 9, and A through F.

Important to know: Binary represents physical signals inside the computer, and hex is an easy way for humans to represent binary numbers

Bit

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The smallest unit of digital information, represented by a 1 or 0.

Byte

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A group of eight bits joined together.

Digital Data

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A physical signal, such as text, numbers, graphics, or sound, interpreted by converting it into binary numbers.

Encoded Integers

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The representation of integers using a group of bytes. Normally, one bit in one of the byes represents the sign, 1 for negative and 0 for positive. The remaining 31 bits are used to encode the number itself using binary digits.

Integers can have a positive or negative value. Computers encode 32 bit by using the first bit for the sign, one for negative and zero for positive. Then, the remaining 31 bits are used to encode the number itself, giving a range from about negative 2 billion to positive 2 billion.

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Encoded Text

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The representation of text by assigning a unique binary code to each character.

Computers represent text by using 1s and 0s as stand-ins for physical signals, such as magnetic or electrical charge. The computer can encode text by assigning a unique binary code to each character.

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Processor Speed

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The speed at which a computer processes information, as measured by the number of cycles per second (Hertz) that the computer's CPU operates at. Processor speed is measured in kilohertz, megahertz, and gigahertz.

In 64-bit processors, computers can receive or send eight bytes of data at once. Each time the processor writes data to memory or reads data from memory is called a cycle. The base unit of measure is hertz (Hz). One hertz means one cycle per second.

• 1 kilohertz (KHz) = 1000 Hz

• 1 megahertz (MHz) = 1 million Hz (Often seen on an older PC bus interfaces.)

• 1 gigahertz (GHz) = 1 billion Hz (Often used with fiber optic networks. Newer computer CPUs run at gigahertz speeds.)

Storage Space

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The measurement in bytes of the volume that a storage device can contain. Storage space is measured in kilobytes (1024 bytes), megabytes (1024 kilobytes), gigabytes (1024 megabytes), and terabytes (1024 gigabytes).

Data storage usually refers to the number of bytes. Since bits and bytes are so small and can't store much information, we use the metric system to describe them in groups.

• 1 kilobyte = 1024 bytes

• 1 megabyte = 1024 kilobytes

• 1 gigabyte = 1024 megabytes

• 1 terabyte = 1024 gigabytes

Throughput

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The measurement in bits per second that information is transferred through a network from one computer to another. Throughput is measured in Kbps (kilobits per second), Mbps (megabits per second), and Gbps (gigabits per second).

Throughput, or data transmission from one computer to another, usually refers to the number of individual bits that can be transmitted in one second. For example, a gigabit internet connection can send a billion ones and zeroes every second. \n \n Throughput is also associated with PC bus speeds, or in other words, how quickly the system bus can move data from one computer component to the other. Some of the most common throughput terms are:

• Kbps (kilobits per second) - 1 Kbps is equal to 1,000 bits per second. This type of throughput is sometimes found in slow network links or in public spaces such as a train.

• Mbps (megabits per second) - 1 Mbps is equal to 1,000,000 bits per second. Often found in home networks and wireless networks. To get the bandwidth available to a memory controller in Mbps, multiply the MHz by 64 and then divide by 8.

• Gbps (gigabits per second) - 1 Gbps is equal to 1,000,000,000 bits per second. Many modern networks and PC bus standards support Gbps.

• Tbps (terabit per second) - 1 Tbps is equal to 1,000,000,000,000 bits per second and is often used when linking data centers, cities, and countries.

ASCII - American Standard Code for Information Interchange

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Pronounced ask-ee and short for American Standard Code for Information Interchange, the most common format for text files in computers on the internet where each character is represented by a unique 7-bit binary code. Extended ASCII uses an 8-bit binary code and allows for international characters.

ASCII was developed in 1963. ASCII is a seven-bit code that can represent 128 different characters (from seven zeroes to seven ones). Each letter and symbol is assigned a number between 0 and 127. With 128 values, it can easily represent the entire English alphabet, the numerals 0 through 9, and the most common punctuation marks. \n \n However, 128 characters aren't sufficient for writing in other languages. Since a byte has eight bits and ASCII uses only seven, there was space to add new characters. Codes 128 through 255 were adapted to meet the needs of other languages. \n \n This system worked well enough for most languages until it became more common to transfer files between computers internationally. For example, résumés sent from Americans to Israel would arrive as rℷsumℷs because the accented é and the Hebrew letter Gimel (ℷ) were both encoded to number 130.

Unicode

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An international 16-bit encoding standard that accommodates character sets from multiple languages, with each letter, digit, or symbol being assigned a unique numeric value.

In 1992, a group called the Unicode Consortium released the first version of Unicode. Unicode uses 16-bit encoding and is capable of representing millions of different text characters. It has enough space for every character from every human language, with room to spare. \n \n Developers have even started assigning Unicode values to pictures, called emoji. Unicode can be implemented by different character encodings standards including UTF-8, UTF-16, and UTF-32. The most commonly used encodings are UTF-8, UTF-16. For example, web pages often used UTF-8 encoding.

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Binary Conversion

Hex Conversion

Kilobyte (KB)

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One kilobyte is equal to 1,000 bytes.

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Megabyte (MB)

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One megabyte is one million bytes of information. Therefore, 1 megabyte equals 1,000 kilobytes.

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Gigabyte (GB)

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One gigabyte is one billion bytes. Therefore, 1 gigabyte equals 1,000 megabytes.

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Terabyte (TB)

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One terabyte is equal to 1,000 gigabytes.

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System memory

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A computer needs memory space available for processing. Processing would be very slow if you had to call up everything to be processed from a mass storage system. Instead, computers are equipped with a system memory that is a storage working space while the computer is running. \n \n Random Access Memory (RAM) is this memory system. However, it is volatile memory. RAM clears all data when the computer shuts down. \n \n Some RAM types include:

• Dynamic RAM (DRAM) is a system RAM that is often used for a computer's main processing memory. A DRAM cell is an integrated circuit composed of a capacitor and a transistor. A data bit is held in the capacitor until the electrical charge is discharged which happens continuously at a slow rate. The DRAM is pulsed with a new electrical charge every few milliseconds in order to retain the data bit.

• Synchronous DRAM (SDRAM) is dynamic RAM that is synchronized to the system bus, the system for communication between the memory and the CPU.

  • Dual Inline Memory Module (DIMM), or RAM stick, is made of several DRAM integrated circuits. They are used for SDRAM in a desktop PC.

  • Small Outline DIMM (SO-DIMM) is a smaller version DIMM that can be used in smaller devices like laptops and tablets.