1.
Neuronal memory allocation
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Memory allocation is a process that determines which specific synapses and neurons in a neural network will store a given memory. Although multiple neurons can receive a stimulus, only a subset of the neurons will induce the necessary plasticity for memory encoding, the selection of this subset of neurons is termed neuronal allocation. Memory allocation was first discovered in the amygdala by Sheena Josselyn. Neuronal allocation is a phenomenon that accounts for how specific neurons in a network, the transcription factor cAMP response element-binding protein is a well-studied mechanism of neuronal memory allocation. Most studies to use the amygdala as a model circuit. CREB modulates cellular processes that lead to neuronal allocation, particularly regards to dendritic spine density. Indeed, Sano and colleagues in the Silva lab showed that CREB also regulates neuronal memory allocation in the amygdala, CREB may be activated by multiple pathways. For example, the cyclic adenosine monophosphate and protein kinase A pathways appear to participate in neuronal allocation, PKA inhibitors can block the development of long-lasting LTP, and this is accompanied by a reduction in the transcription of genes modulated by the CREB protein. Metaplasticity is a term describing the likelihood that a stimulus will induce neuronal plasticity. Several studies provide evidence that neurons receiving “priming activity” minutes to days prior will show a lower threshold for induction of long term potentiation, other studies find that activation of NMDARs can also raise the stimulation threshold for induction of LTP. Thus, similar inputs on groups of neurons may induce LTP in some and these metaplastic effects regulate memory destabilization and reconsolidation. Synaptic allocation pertains to mechanisms that influence how synapses come to store a given memory, allocation of memories to specific synapses are key to determining where memories are stored. Synaptic activity can generate a synaptic tag, which is a marker that allows the spine to subsequently capture newly transcribed plasticity molecules such as Arc. Synaptic activity can also engage the translation and transcription machinery, newly generated plasticity-related proteins can be captured by any tagged synapses, but untagged synapses are not eligible to receive new PPs. After a certain period, synapses will lose their tag. Furthermore, the supply of new PRPs will deplete, the tags and new PRPs must overlap in time to capture the PRPs. The synaptic tag is inversely related to time between inducing stimuli, and is said to be temporarily asymmetrical, furthermore, the tagging is also inversely related to the distance between spines, an important spatial properties of tagging. Overall, these studies demonstrate the complexity of synaptic tagging and capture, Synaptic clustering refers to the addition of new spines to a dendritic area where other spines have been added by previous learning
2.
Operating system
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An operating system is system software that manages computer hardware and software resources and provides common services for computer programs. All computer programs, excluding firmware, require a system to function. Operating systems are found on many devices that contain a computer – from cellular phones, the dominant desktop operating system is Microsoft Windows with a market share of around 83. 3%. MacOS by Apple Inc. is in place, and the varieties of Linux is in third position. Linux distributions are dominant in the server and supercomputing sectors, other specialized classes of operating systems, such as embedded and real-time systems, exist for many applications. A single-tasking system can run one program at a time. Multi-tasking may be characterized in preemptive and co-operative types, in preemptive multitasking, the operating system slices the CPU time and dedicates a slot to each of the programs. Unix-like operating systems, e. g. Solaris, Linux, cooperative multitasking is achieved by relying on each process to provide time to the other processes in a defined manner. 16-bit versions of Microsoft Windows used cooperative multi-tasking, 32-bit versions of both Windows NT and Win9x, used preemptive multi-tasking. Single-user operating systems have no facilities to distinguish users, but may allow multiple programs to run in tandem, a distributed operating system manages a group of distinct computers and makes them appear to be a single computer. The development of networked computers that could be linked and communicate with each other gave rise to distributed computing, distributed computations are carried out on more than one machine. When computers in a work in cooperation, they form a distributed system. The technique is used both in virtualization and cloud computing management, and is common in large server warehouses, embedded operating systems are designed to be used in embedded computer systems. They are designed to operate on small machines like PDAs with less autonomy and they are able to operate with a limited number of resources. They are very compact and extremely efficient by design, Windows CE and Minix 3 are some examples of embedded operating systems. A real-time operating system is a system that guarantees to process events or data by a specific moment in time. A real-time operating system may be single- or multi-tasking, but when multitasking, early computers were built to perform a series of single tasks, like a calculator. Basic operating system features were developed in the 1950s, such as resident monitor functions that could run different programs in succession to speed up processing
3.
User (computing)
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A user is a person who uses a computer or network service. Users generally use a system or a product without the technical expertise required to fully understand it. Power users use advanced features of programs, though they are not necessarily capable of computer programming, a user often has a user account and is identified to the system by a username. Other terms for username include login name, screenname, nickname and handle, some software products provide services to other systems and have no direct end users. End users are the ultimate users of a software product. The term is used to abstract and distinguish those who use the software from the developers of the system. This abstraction is primarily useful in designing the user interface, in user-centered design, personas are created to represent the types of users. It is sometimes specified for each persona which types of user interfaces it is comfortable with, in this context, graphical user interfaces are usually preferred to command-line interfaces for the sake of usability. The end-user development discipline blurs the distinction between users and developers. It designates activities or techniques in which people who are not professional developers create automated behavior, systems whose actor is another system or a software agent have no direct end users. To log in to an account, a user is required to authenticate oneself with a password or other credentials for the purposes of accounting, security, logging. Once the user has logged on, the system will often use an identifier such as an integer to refer to them, rather than their username. In Unix systems, the username is correlated with an identifier or user id. Computer systems operate in one of two based on what kind of users they have, Single-user systems do not have a concept of several user accounts. Multi-user systems have such a concept, and require users to identify themselves using the system. Each user account on a system typically has a home directory, in which to store files pertaining exclusively to that users activities. User accounts often contain a public profile, which contains basic information provided by the accounts owner. Various computer operating-systems and applications expect/enforce different rules for the formats of user names, in some cases, a user may be better known by their username than by their real name, such as CmdrTaco, founder of the website Slashdot
4.
Application software
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An application program is a computer program designed to perform a group of coordinated functions, tasks, or activities for the benefit of the user. Examples of an application include a processor, a spreadsheet, an accounting application, a web browser, a media player, an aeronautical flight simulator. The collective noun application software refers to all applications collectively and this contrasts with system software, which is mainly involved with running the computer. Applications may be bundled with the computer and its software or published separately. Apps built for mobile platforms are called mobile apps, in information technology, an application is a computer program designed to help people perform an activity. An application thus differs from a system, a utility. Depending on the activity for which it was designed, an application can manipulate text, numbers, graphics, some application packages focus on a single task, such as word processing, others, called integrated software include several applications. User-written software tailors systems to meet the specific needs. User-written software includes templates, word processor macros, scientific simulations, graphics. Even email filters are a kind of user software, users create this software themselves and often overlook how important it is. The delineation between system software such as operating systems and application software is not exact, however, and is occasionally the object of controversy. As another example, the GNU/Linux naming controversy is, in part, the above definitions may exclude some applications that may exist on some computers in large organizations. For an alternative definition of an app, see Application Portfolio Management, the word application, once used as an adjective, is not restricted to the of or pertaining to application software meaning. Sometimes a new and popular application arises which only runs on one platform and this is called a killer application or killer app. There are many different ways to divide up different types of application software, web apps have indeed greatly increased in popularity for some uses, but the advantages of applications make them unlikely to disappear soon, if ever. Furthermore, the two can be complementary, and even integrated, Application software can also be seen as being either horizontal or vertical. Horizontal applications are more popular and widespread, because they are general purpose, vertical applications are niche products, designed for a particular type of industry or business, or department within an organization. Integrated suites of software will try to handle every aspect possible of, for example, manufacturing or banking systems, or accounting
5.
Personal computer hardware
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Computer hardware is the collection of physical components that constitute a computer system. By contrast, software is instructions that can be stored and run by hardware, hardware is directed by the software to execute any command or instruction. A combination of hardware and software forms a usable computing system, the template for all modern computers is the Von Neumann architecture, detailed in a 1945 paper by Hungarian mathematician John von Neumann. The meaning of the term has evolved to mean a stored-program computer in which an instruction fetch and this is referred to as the Von Neumann bottleneck and often limits the performance of the system. For the third year, U. S. business-to-business channel sales increased. The impressive growth was the fastest sales increase since the end of the recession, sales growth accelerated in the second half of the year peaking in fourth quarter with a 6.9 percent increase over the fourth quarter of 2012. There are a number of different types of system in use today. The personal computer, also known as the PC, is one of the most common types of computer due to its versatility, laptops are generally very similar, although they may use lower-power or reduced size components, thus lower performance. The computer case is a plastic or metal enclosure that houses most of the components, a case can be either big or small, but the form factor of motherboard for which it is designed matters more. A power supply unit converts alternating current electric power to low-voltage DC power for the components of the computer. Laptops are capable of running from a battery, normally for a period of hours. The motherboard is the component of a computer. It is usually cooled by a heatsink and fan, or water-cooling system, most newer CPUs include an on-die Graphics Processing Unit. The clock speed of CPUs governs how fast it executes instructions, many modern computers have the option to overclock the CPU which enhances performance at the expense of greater thermal output and thus a need for improved cooling. The chipset, which includes the bridge, mediates communication between the CPU and the other components of the system, including main memory. Random-Access Memory, which stores the code and data that are being accessed by the CPU. For example, when a web browser is opened on the computer it takes up memory, RAM usually comes on DIMMs in the sizes 2GB, 4GB, and 8GB, but can be much larger. Read-Only Memory, which stores the BIOS that runs when the computer is powered on or otherwise begins execution, the BIOS includes boot firmware and power management firmware
6.
Process management (computing)
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Process management is an integral part of any modern-day operating system. The OS must allocate resources to processes, enable processes to share and exchange information, protect the resources of each process from other processes and enable synchronization among processes. With some programs, it is possible to have one copy loaded into memory, such a program is said to be re-entrant. A number of processes being executed over a period of time instead of at the time is called concurrent execution. A multiprogramming or multitasking OS is a system executing many processes concurrently, Multiprogramming requires that the processor be allocated to each process for a period of time and de-allocated at an appropriate moment. If the processor is de-allocated during the execution of a process, a hardware interrupt occurs, for example, a key was pressed on the keyboard, or a timer runs out. The stopping of one process and starting of another process is called a switch or context change. In many modern operating systems, processes can consist of many sub-processes and this introduces the concept of a thread. A thread may be viewed as a sub-process, that is, threads are becoming increasingly important in the design of distributed and client–server systems and in software run on multi-processor systems. A common trait observed among processes associated with most computer programs, is that they alternate between CPU cycles and I/O cycles, for the portion of the time required for CPU cycles, the process is being executed, i. e. is occupying the CPU. During the time required for I/O cycles, the process is not using the processor, instead, it is either waiting to perform Input/Output, or is actually performing Input/Output. An example of this is the reading from or writing to a file on disk, prior to the advent of multiprogramming, computers operated as single-user systems. Computer scientists observed that overall performance of the machine could be improved by letting a different process use the processor whenever one process was waiting for input/output, in a uni-programming system, if N users were to execute programs with individual execution times of t1, t2. TN, then the time, tuni, to service the N processes of all N users would be. However, because each process consumes both CPU cycles and I/O cycles, the time each process actually uses the CPU is a very small fraction of the total execution time for the process. To overcome this inefficiency, multiprogramming is now implemented in operating systems such as Linux, UNIX. This enables the processor to switch from one process, X, to another, Y, in a very simple system designed for running only a single application, it may be possible to have all the processes that will ever be needed be present when the system comes up. In general-purpose systems, however, some way is needed to create and terminate processes as needed during operation, there are four principal events that cause a process to be created, System initialization
7.
Interrupt
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In system programming, an interrupt is a signal to the processor emitted by hardware or software indicating an event that needs immediate attention. An interrupt alerts the processor to a high-priority condition requiring the interruption of the current code the processor is executing, the processor responds by suspending its current activities, saving its state, and executing a function called an interrupt handler to deal with the event. This interruption is temporary, and, after the interrupt handler finishes, there are two types of interrupts, hardware interrupts and software interrupts. Hardware interrupts are used by devices to communicate that they require attention from the operating system, for example, pressing a key on the keyboard or moving the mouse triggers hardware interrupts that cause the processor to read the keystroke or mouse position. Unlike the software type, hardware interrupts are asynchronous and can occur in the middle of instruction execution, the act of initiating a hardware interrupt is referred to as an interrupt request. A software interrupt is caused either by a condition in the processor itself. The former is called a trap or exception and is used for errors or events occurring during program execution that are exceptional enough that they cannot be handled within the program itself. For example, an exception will be thrown if the processors arithmetic logic unit is commanded to divide a number by zero as this instruction is in error. The operating system will catch this exception, and can choose to abort the instruction, each interrupt has its own interrupt handler. The number of interrupts is limited by the number of interrupt request lines to the processor. Interrupts are a commonly used technique for computer multitasking, especially in real-time computing, such a system is said to be interrupt-driven. Hardware interrupts were introduced as an optimization, eliminating unproductive waiting time in polling loops and they may be implemented in hardware as a distinct system with control lines, or they may be integrated into the memory subsystem. If implemented as part of the controller, interrupts are mapped into the systems memory address space. Interrupts can be categorized into different types, Maskable interrupt. Non-maskable interrupt, an interrupt that lacks an associated bit-mask. NMIs are used for the highest priority tasks such as timers, inter-processor interrupt, a special case of interrupt that is generated by one processor to interrupt another processor in a multiprocessor system. Software interrupt, an interrupt generated within a processor by executing an instruction, software interrupts are often used to implement system calls because they result in a subroutine call with a CPU ring level change. Spurious interrupt, an interrupt that is unwanted
8.
File system
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In computing, a file system or filesystem is used to control how data is stored and retrieved. Without a file system, information placed in a storage medium would be one large body of data with no way to tell where one piece of information stops, by separating the data into pieces and giving each piece a name, the information is easily isolated and identified. Taking its name from the way paper-based information systems are named, the structure and logic rules used to manage the groups of information and their names is called a file system. There are many different kinds of file systems, each one has different structure and logic, properties of speed, flexibility, security, size and more. Some file systems have been designed to be used for specific applications, for example, the ISO9660 file system is designed specifically for optical discs. File systems can be used on different types of storage devices that use different kinds of media. The most common device in use today is a hard disk drive. Other kinds of media that are used include flash memory, magnetic tapes, in some cases, such as with tmpfs, the computers main memory is used to create a temporary file system for short-term use. Some file systems are used on local storage devices, others provide file access via a network protocol. Some file systems are virtual, meaning that the files are computed on request or are merely a mapping into a different file system used as a backing store. The file system access to both the content of files and the metadata about those files. It is responsible for arranging storage space, reliability, efficiency, before the advent of computers the term file system was used to describe a method of storing and retrieving paper documents. By 1961 the term was being applied to computerized filing alongside the original meaning, by 1964 it was in general use. A file system consists of two or three layers, sometimes the layers are explicitly separated, and sometimes the functions are combined. The logical file system is responsible for interaction with the user application and it provides the application program interface for file operations — OPEN, CLOSE, READ, etc. and passes the requested operation to the layer below it for processing. The logical file system manage open file table entries and per-process file descriptors and this layer provides file access, directory operations, security and protection. The second optional layer is the file system. This interface allows support for multiple concurrent instances of physical file systems, the third layer is the physical file system
9.
Device driver
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In computing, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer. A driver communicates with the device through the bus or communications subsystem to which the hardware connects. When a calling program invokes a routine in the driver, the driver issues commands to the device, once the device sends data back to the driver, the driver may invoke routines in the original calling program. Drivers are hardware dependent and operating-system-specific and they usually provide the interrupt handling required for any necessary asynchronous time-dependent hardware interface. The main purpose of device drivers is to provide abstraction by acting as a translator between a device and the applications or operating systems that use it. Programmers can write the higher-level application code independently of specific hardware the end-user is using. For example, an application for interacting with a serial port may simply have two functions for send data and receive data. At a lower level, a device driver implementing these functions would communicate to the serial port controller installed on a users computer. Writing a device driver requires an understanding of how the hardware. In contrast, most user-level software on modern operating systems can be stopped without greatly affecting the rest of the system, even drivers executing in user mode can crash a system if the device is erroneously programmed. These factors make it difficult and dangerous to diagnose problems. The task of writing drivers thus usually falls to software engineers or computer engineers who work for hardware-development companies and this is because they have better information than most outsiders about the design of their hardware. Moreover, it was considered in the hardware manufacturers interest to guarantee that their clients can use their hardware in an optimum way. Typically, the Logical Device Driver is written by the operating system vendor, but in recent years non-vendors have written numerous device drivers, mainly for use with free and open source operating systems. In such cases, it is important that the manufacturer provides information on how the device communicates. Although this information can instead be learned by reverse engineering, this is more difficult with hardware than it is with software. Microsoft has attempted to reduce system instability due to poorly written device drivers by creating a new framework for driver development, if such drivers malfunction, they do not cause system instability. Apple has a framework for developing drivers on Mac OS X called the I/O Kit
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. doi:10.1002/spe.4380240602.
