ITCC 111: Evolution of Computing PDF

**ITCC 111** **LESSON : EVOLUTION OF COMPUTING** **Definition of computer** **Computer** is a programmable machine. **Computer** is a machine that manipulates data according to a list of instructions. **Computer** is any device which aids humans in performing various kinds of computations or ca...

**ITCC 111** **LESSON : EVOLUTION OF COMPUTING** **Definition of computer** **Computer** is a programmable machine. **Computer** is a machine that manipulates data according to a list of instructions. **Computer** is any device which aids humans in performing various kinds of computations or calculations. Three principles characteristic of computer: - It responds to a specific set of instructions in a well-defined manner. - It can execute a pre-recorded list of instructions. - It can quickly store and retrieve large amounts of data. **Earliest Computer** - Originally calculations were computed by humans whose job title was computers. - These human computers were typically engaged in the calculation of a mathematical expression. - The calculations of this period were specialized and expensive, requiring years of training in mathematics. - The first use of the word \"**computer**\" was recorded in 1613, referring to a person who carried out calculations, or computations, and the word continued to be used in that sense until the middle of the 20th century. a. **Tally** **Sticks** - was an ancient memory aid device to record and document numbers, quantities, or even messages. b. **Abacus** - is a mechanical device used to aid an individual in performing mathematical calculations. And was beads on rods to count and calculate. It was still widely used in Asia. c. **Napier's Bones** - Invented by John Napier in 1614. And is allowed the operator to multiply, divide and calculate square and cube roots by moving the rods around and placing them in specially constructed boards. d. **Slide Rule** - Invented by William Oughtred in 1622. And is based on Napier\'s ideas about logarithms e. **Stepped Reckoner** - Invented by Gottfried Wilhelm Leibniz in 1672. And the machine that can add, subtract, multiply and divide automatically. f. **Jacquard Loom** - The Jacquard loom is a mechanical loom, invented by Joseph-Marie Jacquard in 1881. The Jacquard concept of recording data in the form of holes punched in cards was used in the design of punched card information processing equipment. g. **Arithmometer** - A mechanical calculator invented by Thomas de Colmar in 1820, The first reliable, useful and commercially successful calculating machine. The machine could perform the four basic mathematic functions. The first mass-produced calculating machine. h. **Difference Engine and Analytical Engine** - A difference engine is an automatic, mechanical calculator designed to tabulate polynomial functions. The analytical engine is the first mechanical computer. Invented by Charles. **First Computer Programmer** - In 1840, **Augusta Ada Byron** or commonly known as **Ada Lovelace** suggested Babbage that he use the binary system. - She wrote programs for the Analytical Engine. **Scheutzian Calculation Engine** - Invented by Per Georg Scheutz in 1843. - Based on Charles Babbage's difference engine. - The **first printing calculator**. **Tabulating Machine** - Invented by **Herman Hollerith** in 1890. - To assist in summarizing information and accounting. **Harvard Mark 1** - Also known as **IBM Automatic Sequence Controlled Calculator (ASCC).** - Invented by **Howard H. Aiken** in 1943. - The **first electro-mechanical computer**. **Z1** - **The first programmable computer**. - Created by **Konrad Zuse** in Germany from 1936 to 1938. - To program the Z1 required that the user insert punch tape into a punch tape reader and all output was also generated through punch tape. **Atanasoff-Berry Computer (ABC)** - It was the first electronic digital computing device. - Invented by **Professor John Atanasoff** and graduate **student** **Clifford Berry** at Iowa State University between 1939 and 1942. **ENIAC** - ENIAC stands for **Electronic Numerical Integrator and Computer**. - It was the **first electronic general-purpose computer**. - Completed in 1946. - Developed by **John Presper Eckert** and **John W. Mauchl**. - There were also **six female programmers involved**. **EDVAC** - EDVAC stands for **Electronic Discrete Variable Automatic Computer.** - The First Stored Program Computer. - Designed by **Von Neumann** in 1952. - It has a memory to hold both a stored program as well as data. **The First Portable Computer** - **Osborne 1** -- the first portable computer. It was released in 1981 by the **Osborne Computer Corporation**. **The First Computer Company** - The first computer company was the **Electronic Controls Company**. It was founded in 1949 by J. **Presper Eckert** and **John Mauchly**. **Computer Generations:** a. **First Generation** -- 1946 - 1958 b. **Second Generation** -- 1959 - 1964 c. **Third Generation** -- 1965 - 1970 d. **Fourth Generation** -- 1971 - Present e. **Fifth** **Generation** -- Present -- Onwards Advancement to Modern Computers What was the biggest advance that led to modern computers? - **Electricity** - **Transistor** - **Microchip** - **Data storage** **First Generation** (1946-1958) - The first computers used vacuum tubes for circuitry and magnetic drums for memory, and were often enormous, taking up entire rooms. - They were very expensive to operate and in addition to using a great deal of electricity, generated a lot of heat, which was often the cause of malfunctions. - First generation computers relied on machine language, the lowest-level programming language understood by computers, to perform operations, and they could only solve one problem at a time. - Input was based on punched cards and paper tape, and output was displayed on printouts. **Vacuum Tubes** - First Generation Electronic Computers used Vacuum Tubes - Vacuum tubes are glass tubes with circuits inside. - Vacuum tubes have no air inside of them, which protects the circuitry. **Univac -- 1951** - First fully electronic digital computer built in the U.S. - Designed by J. Presper Eckert and John Mauchly. - ENIAC weighed 30 tons contained 18,000 vacuum tubes - Cost a paltry \$487,000 **Grace Hopper** - Programmed UNIVAC - Recipient of Computer - Science's first "Man of the Year Award" **First Computer Bug -- 1945** - Relay switches part of computers. - Grace Hopper found a moth stuck in a relay responsible for a malfunction. - Called it "debugging" a computer. **Second Generation (1959 - 1964)** - Transistors replaced vacuum tubes and ushered in the second generation of computers. - One transistor replaced the equivalent of 40 vacuum tubes. - Allowing computers to become smaller, faster, cheaper, more energy-efficient and more reliable. - Still generated a great deal of heat that can damage the computer. - Second-generation computers moved from cryptic binary machine language to symbolic, or assembly, languages, which allowed programmers to specify instructions in words. - Second-generation computers still relied on punched cards for input and printouts for output. - These were also the first computers that stored their instructions in their memory, which moved from a magnetic drum to magnetic core technology. - 1956 -- Computers began to incorporate Transistors. - Replaced vacuum tubes with Transistors. **First Transistor** - Uses Silicon. - Developed in 1948. - The Nobel Prize in Physics 1956 was awarded jointly to William Bradford Shockley, John Bardeen and Walter Houser Brattain. - Second Generation Computers used Transistors, starting in 1956. **Third Generation (1965 -- 1970)** - Integrated Circuit - Operating System - Getting smaller, cheaper - The development of the integrated circuit was the hallmark of the third generation of computers. - Transistors were miniaturized and placed on silicon chips, called semiconductors, which drastically increased the speed and efficiency of computers. - Much smaller and cheaper compared to the second-generation computers. - It could carry out instructions in billionths of a second. - Users interacted with third generation computers through keyboards and monitors and interfaced with an operating system, which allowed the device to run many different applications at one time with a central program that monitored the memory. - Computers for the first time became accessible to a mass audience because they were smaller and cheaper than their predecessors. **Integrated Circuits** - Third Generation Computers used Integrated Circuits (chips). - Integrated Circuits are transistors, resistors, and capacitors integrated together into a single "chip". **Operating System** - Software -- Instructions for Computer. - Operating system is set of instructions loaded each time a computer is started. - Program is instructions loaded when needed. **Microprocessor -- 1971** - Intel 4004 Microprocessor - The 4004 had 2,250 transistors - Four-bit chunks (four 1's or 0's) - 108Khz - Called "Microchip" **Fourth Generation (1971-present)** - MICROCHIPS - Getting smaller and smaller, but we are still using microchip technology. - As these small computers became more powerful, they could be linked together to form networks, which eventually led to the development of the Internet. - Fourth generation computers also saw the development of GUIs, the mouse and handheld devices. **What is a Microchip?** - Very Large-Scale Integrated Circuit (VLSIC). - Transistors, resistors, and capacitors. - 4004 had 2,250 transistors. - Pentium IV has 42 MILLION transistors. - Each transistor 0.13 microns (10-6 meters). **Personal Computers** - MITS Altair - 256-byte memory (not Kilobytes or Megabytes) - 2 MHz Intel 8080 chips - Just a box with flashing lights - Cost \$395 kit, \$495 assembled **Electronics** Vacuum Tube - a dinosaur without a modern lineage. Transistor to Integrated Circuit to Microchip. **Ibm pc -- 1981** - IBM-Intel-Microsoft joint venture. - First wide-selling personal computer used in business. - 8088 Microchip - 29,000 transistors - 4.77 Mhz processing speed - 256 K RAM (Random Access Memory) standard. - One or two floppy disk drives. **Apple Computers** - Founded 1977 - Apple II released 1977 - Widely used in schools - Macintosh - Released in 1984, Motorola 68000 Microchip processor. - First commercial computer with graphical user interface (GUI) and pointing device (mouse) **1990s: Pentiums & Power macs** - Early 1990s began penetration of computers into every niche: every desk, most homes, etc. - Faster, less expensive computers paved way for this. - Windows 95 was first decent GUI for "PCs". - Macs became more PC compatible - easy file transfers. - Prices have plummeted. - \$2000 for entry level to \$500. - \$6000 for top of line to \$1500. **Fourth Generation** - The microprocessor brought the fourth generation of computers, as thousands of integrated circuits were built onto a single silicon chip. **Fifth Generation (PRESENT-ONWARDS)** - Based on Artificial Intelligence (AI). - Still in development. - The use of parallel processing and superconductors is helping to make artificial intelligence a reality. - The goal is to develop devices that respond to natural language input and are capable of learning and self-organization. - There are some applications, such as voice recognition, that are being used today. **SUMMARY:** - The first use of the word \"computer\" was recorded in 1613, referring to a person who carried out calculations, or computations. - Tally sticks is an ancient memory aid device to record and document numbers, quantities, or even messages. - Abacus is a mechanical device in performing mathematical calculations. - Napier's bones was invented by John Napier in 1614. - Slide rule was invented by William Oughtred in 1622. - Stepped reckoner was invented by Gottfried Wilhelm Leibniz in 1672. - Jacquard loom is a mechanical loom that records data in the form of holes punched in cards that was invented by JosephMarie Jacquard in 1881. - Arithmometer is a mechanical calculator invented by Thomas de Colmar in 1820. - The difference engine and analytical engine was invented by Charles Babbage in 1822 and 1834 and is considered to be the first mechanical computer. - The first computer programmer was Ada Lovelace. - The first printing calculator was invented by Per Georg Scheutz in 1843 coined as Scheutizian Calculation Engine. - The tabulating machine was invented by Herman Hollerith in 1890. - Harvard Mark 1 is the first electro-mechanical computer. - Z1 is the first programmable computer. - The first electronic digital computing device is the AtanasoffBerry Computer (ABC). - ENIAC is the first electronic general-purpose computer which was completed in 1946. - EDVAC is the first stored program computer which was designed by Von Neumann in 1952. - Osborne 1 is the the first portable computer. - The first computer company is the Electronic Controls Company. - The first generation focused on the use of vacuum tubes for circuity and magnetic drums for memory. - First generation relied on machine language. - Grace Hopper programmed the UNIVAC. - The first computer but was in 1945, Grace Hopper found a moth that caused the malfunction. - The second generation replaces vacuum tubers and used transistors. - Transistors are smaller, faster, cheaper, more energy-efficient, and more reliable. - The third generation used the technology of integrated circuits. It had miniaturized transistors and placed on silicon chips called semiconductors. - The users could interact with keyboard and monitors and the interface with an operating system. - Fourth generation was brought on by the microprocessor, small computers become more powerful. - Improvement on the GUIs, mouse, and handheld devices were seen in the fourth generation. - Fifth generation is still in development, it is based on artificial intelligence, and the use of parallel processing and superconductors **LESSON : COMPUTER BASIC** Understanding Information Systems **Information System**: An interconnected environment for managing and processing data using a computer Parts of an information system: - **People** - **Hardware** - **Software** - **Procedures** - **Data** **Computer Types** - Personal Computers a. **Desktop PC** - System unit, separate monitor, keyboard, mouse. b. **Notebook PC** - Fold-up design, built-in keyboard and screen. c. **Tablet** **PC** - Slate design, touch screen, no separate keyboard, mouse, or monitor. d. **Smartphone** - Hand-held, phone and computer, touch screen. **Computer Types** - Multi-User Computers -- Server. - Serves and supports a network. - Provides centrally accessible storage space. - Shares printers. - Does not directly provide processing power to clients. a. **Mainframe** - Collects large amounts of business data. - Provides processing support to terminals. b. **Supercomputer** - Largest computer available. - Universities, research, government. **Software Types** a. **Basic Input Output System (BIOS)** - Read-only chip on motherboard. - Startup instructions for computer. b. **Operating System (OS)** - User interface. - Runs application. - File storage. - Communication with hardware. c. **Utilities - Error correction, optimization, protection.** d. **Application Software** - Productivity tools, graphics, games, multimedia. e. **Productivity Software.** f. **Helps you accomplish practical tasks.** **Information Processing Cycle DESKTOP COMPONENTS**  **HOW DATA IS REPRESENTED** **Information Processing** a. **Input** - Keyboard, pointing devices, digital cameras, scanners, bar code readers b. **Processing** - Motherboard, CPU, memory, buses, chipset c. **Output** - Monitor, printer d. **Storage** - Hard drive, USB flash drive, CD, DVD **Ethernet Networking** a. **Ethernet Networking** - Wired Ethernet - Wi-Fi (802.11) b. **Hardware** - Network interface card (NIC), a.k.a. network adapter - Switch - Router - Cable (copper, fiber optic) c. **Types of Networks** - Client/server - Peer to Peer **Other Ways Computers Communicate** a. **Bluetooth** - Short-range personal networking - Device connectivity b. **Internet** - Dial-up - Broadband - Internet service provider - TCP/IP **Part of an Information System** a. **People**: To help people accomplish their goals. b. **Hardware**: Physical parts of a computer system. c. **Software**: Tells the hardware what to do. (OS or Application). d. **Procedures**: The software doesn't run itself (usually). People must interact with the computer to tell it what software to run. e. **Data**: Computer programs operate upon the data they receive. **Ethernet Networking** - A network adapter enables a computer to participate in the local area network. - While a network switch can connect multiple devices and networks to expand the LAN, a router will allow you to share a single IP address among multiple network devices. - Ethernet switch creates networks, and the router allows for connections between networks **Information Processing Cycle** a. **Input**: Components that help humans put data into the computer. Examples include a keyboard, mouse, and touch screen. b. **Processing**: Components that move and process the data inside the computer. The motherboard and its processor and memory chips fall into this category. c. **Output**: Components that provide the results of the processing to humans. The monitor is the primary output device; other examples include printers and speakers. d. **Storage**: Components that store software and data until it is needed. Storage components include hard drives, USB flash drives, and DVDs. **Software** **as** **a Service (SaaS)** - Did you know that you can also use some software without installing it on your computer? Software as a Service (SaaS) is a new way of thinking about accessing and paying for software. Rather than buying a software product once, installing it on your computer and "owning" it forever, with the SaaS model you pay a usage fee for the software, which remains the property of the company. The software and any associated data are stored online. The company provides free updates for as long as you keep renewing your usage. Microsoft Office can optionally be rented this way through the Office 365 program, and many other applications are also being offered as services. - SaaS has many benefits. The cost is typically lower than for buying the software outright, and updates and new versions are free and automatically provided. 1. What are the five parts of an information system? - People - Hardware - Software - Procedures - Data 2. What is the difference between a server and a mainframe? a. Server - Serves and supports a network - Provides centrally accessible storage space - Shares printers - Does not directly provide processing power to clients b. Mainframe - Collects large amounts of business data - Provides processing support to terminals 3. What distinguishes an operating system from an application? a. Basic Input Output System (BIOS) - Read-only chip on motherboard - Startup instructions for computer b. Application Software - Productivity tools, graphics, games, multimedia 4. What are the four parts of the information processing cycle? - Input - Processing - Output - Storage 5. What is Wi-Fi and what equipment does it require? - Wi-Fi Wireless Ethernet. A means of connecting computers and other devices wirelessly. Another name for it is IEEE 802.11, its technical standard. - Broadband is a fast, always-on network connection. - Router A connection box for Ethernet networks that physically joins the devices in the network (wired) or provides wireless connectivity (wireless), and enables a connection to an outside network such as the Internet. **LESSON : THE SYSTEM UNIT** **Understanding CPUs** - **Central Processing Unit (CPU)** -Control Unit - Manages the flow of data through the CPU - **Arithmetic Logic Unit (ALU)** -Does the actual processing - Registers -Holding areas for data and instructions **Understanding CPUs The Machine Cycle** **Physical Composition of a CPU** - Semiconductor material (silicon). - Encased in a ceramic shell. - Mounted on a small circuit board. - Pins or contacts on the underside. **Cores** - Most modern PC CPUs have multiple cores. - Common numbers of cores are 2, 4, or 6. - Each core has its own control unit, ALU, and registers. - Multiple cores allow parallel processing for greater throughput. **Caches** - Cache is a small amount of fast memory located in or near the CPU - Stores recently used data or data soon to be used - Helps limit latency to improve performance - Multi-level cache system - L1, L2, L3 - L1 is smallest, fastest, closest to core - Fetching from L3 takes 10 times as long as from L1 **CPU Performance Factors** - Speed (in gigahertz, GHz) - Instructions per Second - Word size (32-bit or 64-bit) **Understanding** **Memory** a. **Static vs. Dynamic Memory** - **Static** = non-volatile - **Dynamic** = volatile b. **Random Access Memory (RAM) vs. Read Only Memory (ROM)** - **RAM** = rewriteable - **ROM** = not rewriteable (with exceptions) - **Electrically Erasable Programmable ROM (EEPROM),** basis for solid-state drives and USB flash drives **How Computers Use Memory** - System memory (main memory) - Component memory (printers, display adapters) - ROM-BIOS (EEPROM chip) - CPU caches - USB flash drives - Memory cards - Solid-state hard drives **Understanding System Memory** - Main memory is dynamic RAM (DRAM) - Virtual memory is simulated memory from data swapping on/off the hard drive - Paging file is the area of the hard drive dedicated for virtual memory - Memory addresses **Memory's Physical Form** - Dual inline memory modules (DIMMs) - Small-outline DIMMs (SO-DIMMs) for portables - Memory capacity per DIMM - 2GB, RGB, 16GB, etc. - Synchronous DRAM (SDRAM) synchronizes with the system bus speed - Double data rate (DDR) SDRAM -0 DDR2, DDR3, DDR4 **Understanding Motherboards** - **Motherboard**: large circuit board inside the computer - Capabilities dictated by **Chipset** - **Form Factor**: size and shape of motherboard - **Expansion** **Slots** in desktop motherboard, for expansion cards \- PCI \- PCI Express (PCIe), x1, x4, x16 - **ExpressCard** slot in notebooks - PCI Express Mini Card socket in notebooks **Built In Components** a. **Graphics Ports:** - Digital Visual Interface (DVI) - Video Graphics Array (VGA) b. **Speakers/Headphones** - 3.5 mm c. **Ethernet** **Networking** - RJ-45 jack - Resembles a wide telephone plug d. **Universal Serial Bus (USB)** - USB 1.1, 2.0, 3.0 speeds e. **FireWire (IEEE 1394)** **Built In Components (Legacy)** a. PS/2 - Used for older keyboards and mice b. Parallel Port - Used for older printers c. Serial Port - Used only for very old components (mice, modems) **Drive** **Connectors** a. **Parallel ATA** - Older hard disk drives - Older CD and DVD drives b. **Serial ATA** - Newer hard disk drives. - Newer CD and DVD drives. - Solid-state hard drives. **Understanding Power Supplies** a. Power supply has two functions: - Converts AC to DC. - Decreases the voltage to the appropriate levels for the devices it powers. **Wire Colors** **Notebook Power Supply** - Transformer block (brick) **Troubleshooting System Unit Problems** a. **No Response** - Check for power - Hold down Power button for 10 seconds, then press it again - Do a soft reset (mobile device) - Do a hard reset (mobile device) b. **Fan Noise but Nothing Onscreen** - Power-on Self-Test (POST) card diagnostic - Remove all non-essential hardware - Remove newly installed hardware c. **Error Message on Black Screen** - Troubleshoot according to the message received - Research error message online - Use CMOS Setup (BIOS Setup) to adjust settings or check device status d. **Error Message on Bright Blue Screen** - "Blue Screen of Death" (BSOD) - Turn computer off and back on again - If error persists, there may be a hardware incompatibility or failure e. **Windows Hangs at Startup** - Restart in Safe Mode - Prevent non-essential drivers and programs from loading\\ f. **PC Shuts Down or Freezes** - Most likely overheating **LESSON : COMPUTER HARDWARE** Hardware refers to the external and internal devices and equipment that enable you to perform major functions such as input, output, storage, communication, processing, and more. There are two types of computer hardware: external and internal. External hardware devices include monitors, keyboards, printers, and scanners, whereas internal hardware devices include motherboards, hard drives, and RAM. **Input** **Devices**: Let's you communicate with a computer. You can use input devices to enter information and issue commands. **Output** **Devices**: An output device displays information on a screen, creates a printed copy, or generate sound**System** **Unit**: System unit is the part of the computer which is responsible for accepting and processing the data brought in by the input devices. **System** **Unit** **Motherboard:** - the primary device of the system unit. All other devices are connected to it. The motherboard unites all computer devices (video card, RAM, sound card, hard drive, etc.) and links them together, subsequently regulating their close-knit work. - The main purpose is to connect all computer nodes into one device, so, by and large, this is just a set of wires between the processor contacts and the contacts of memory modules and peripheral devices. **Processor:** - is an incredibly complex chip that performs billions of mathematical calculations per second. It is also called a central processing unit (CPU). - is the core of the computer, so to speak, its central brain, the component that performs the bulk of the computer's work. Data from other details is sent to the processor for calculations. After mathematical calculations, the data is returned to the various devices that use it. **RAM** (**Random** **Access** **Memory**): - system memory. The RAM is connected directly to the motherboard and carries out a fast exchange of information with the processor. - aims to store and quickly access data. All information on it is lost after the power is turned off. **Hard** **Drive**: - a mechanical drive that works on the principle of magnetic recording, is the central storage of data on most computers. - Hard Drive is designed to store music, videos, photos, documents, and other files in the computer's permanent memory. **Video** **Card** **or** **Graphics** **Card**: - graphics accelerator, a computer component responsible for generating and displaying images. Modern Video Cards support HDMI (High Definition Multimedia Interface), VGA (Video Graphics Array), and DVI (Digital Visual Interface). - converts the image in the computer's memory into a video signal for the monitor. **Power** **Supply**: - a component that converts electrical energy into direct current required by the computer. - provides power to the PC. It also performs the functions of stabilization and protection against minor interference in the electrical network. **LESSON : TYPES OF COMPUTER SOFTWARE** 1. **Application Software -** It is designed to perform specific tasks or functions for end-users. Its purpose is to enable users to accomplish their goals efficiently and effectively using computer technology. **Categories of Application Software -** Application software can be categorized into various types based on its intended use, such as productivity software (e.g., Microsoft Office), entertainment software (e.g., video games), and educational software (e.g., language learning apps). 2. **SYSTEM** **SOFTWARES -** System software is a type of software that provides a platform for running application software and manages computer hardware resources. Its primary role is to facilitate communication between hardware components and application programs. **Components of System Software -** includes operating systems (e.g., Windows, macOS), which provide a user interface and manage system resources, as well as device drivers, which enable communication between hardware devices and the operating system. System software plays a critical role in managing hardware resources, such as memory and storage, and providing users with a means to interact with the computer system through graphical user interfaces (GUIs) or command-line interfaces (CLIs). 3. **UTILITY** **SOFTWARES** - Consists of programs designed to perform specific tasks related to system maintenance, optimization, and security. Its functions typically focus on enhancing system performance, managing resources, and ensuring the security of data and applications. Utility software helps improve system performance by optimizing resource usage, removing unnecessary files, and protecting against security threats. It contributes to a smoother user experience by addressing common maintenance tasks and enhancing system stability. Summary: Software is a fundamental component of computing, comprising various types that serve distinct purposes. Application Software: Designed for end-users to perform specific tasks.Examples: Word processors, web browsers, graphic design tools.Categories: Productivity, entertainment, educational. System Software:Provides a platform for running applications, manages hardware.Examples: Operating systems (e.g., Windows, macOS), device drivers.Role: Facilitates communication between hardware and application programs. Utility Software:Programs for system maintenance, optimization, and security.Examples: Antivirus software, disk cleanup tools, file compression utilities.Functions: Enhances system performance, manages resources, ensures security.