Computer system in the context of Processing power

An embedded system is a specialized computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is embedded as part of a complete device often including electrical or electronic hardware and mechanical parts. Because an embedded system typically controls physical operations of the machine that it is embedded within, it often has real-time computing constraints. Embedded systems control many devices in common use. In 2009, it was estimated that ninety-eight percent of all microprocessors manufactured were used in embedded systems.

Modern embedded systems are often based on microcontrollers (i.e. microprocessors with integrated memory and peripheral interfaces), but ordinary microprocessors (using external chips for memory and peripheral interface circuits) are also common, especially in more complex systems. In either case, the processor(s) used may be types ranging from general purpose to those specialized in a certain class of computations, or even custom designed for the application at hand. A common standard class of dedicated processors is the digital signal processor (DSP).

In computing, an icon is a pictogram or ideogram displayed on a computer screen in order to help the user navigate a computer system. It can serve as an electronic hyperlink or file shortcut to access the program or data. The user can activate an icon using a mouse, pointer, finger, or voice commands. Their placement on the screen, also in relation to other icons, may provide further information to the user about their usage. In activating an icon, the user can move directly into and out of the identified function without knowing anything further about the location or requirements of the file or code.

Icons as parts of the graphical user interface of a computer system, in conjunction with windows, menus and a pointing device (mouse), belong to the much larger topic of the history of the graphical user interface that has largely supplanted the text-based interface for casual use.

In computing, an emulator is hardware or software that enables one computer system (called the host) to behave like another computer system (called the guest). An emulator typically enables the host system to run software or use peripheral devices designed for the guest system.Emulation refers to the ability of a computer program in an electronic device to emulate (or imitate) another program or device.

Many printers, for example, are designed to emulate HP LaserJet printers because a significant amount of software is written specifically for HP models. If a non-HP printer emulates an HP printer, any software designed for an actual HP printer will also function on the non-HP device, producing equivalent print results. Since at least the 1990s, many video game enthusiasts and hobbyists have used emulators to play classic arcade games from the 1980s using the games' original 1980s machine code and data, which is interpreted by a current-era system, and to emulate old video game consoles (see video game console emulator).

In computing, a virtual machine (VM) is the virtualization or emulation of a computer system. Virtual machines are based on computer architectures and provide the functionality of a physical computer. Their implementations may involve specialized hardware, software, or a combination of the two.Virtual machines differ and are organized by their function, shown here:

• System virtual machines (also called full virtualization VMs, or SysVMs) provide a substitute for a real machine. They provide the functionality needed to execute entire operating systems. A hypervisor uses native execution to share and manage hardware, allowing for multiple environments that are isolated from one another yet exist on the same physical machine. Modern hypervisors use hardware-assisted virtualization, with virtualization-specific hardware features on the host CPUs providing assistance to hypervisors.
• Process virtual machines are designed to execute computer programs in a platform-independent environment.

Some virtual machine emulators, such as QEMU and video game console emulators, are designed to also emulate (or "virtually imitate") different system architectures, thus allowing execution of software applications and operating systems written for another CPU or architecture. OS-level virtualization allows the resources of a computer to be partitioned via the kernel. The terms are not universally interchangeable.

Software requirements for a system are the description of what the system should do, the service or services that it provides and the constraints on its operation. The IEEE Standard Glossary of Software Engineering Terminology defines a requirement as:

1. A condition or capability needed by a user to solve a problem or achieve an objective
2. A condition or capability that must be met or possessed by a system or system component to satisfy a contract, standard, specification, or other formally imposed document
3. A documented representation of a condition or capability as in 1 or 2

The activities related to working with software requirements can broadly be broken down into elicitation, analysis, specification, and management.

In computing, computer performance is the amount of useful work accomplished by a computer system. Outside of specific contexts, computer performance is estimated in terms of accuracy, efficiency and speed of executing computer program instructions. When it comes to high computer performance, one or more of the following factors might be involved:

• Short response time for a given piece of work.
• High throughput (rate of processing work tasks).
• Low utilization of computing resources.
  • Fast (or highly compact) data compression and decompression.
• High availability of the computing system or application.
• High bandwidth.
• Short data transmission time.

A port operator is a port authority or company that contracts with the port authority to move cargo through a port at a contracted minimum level of productivity. They may be state-owned (particularly for port authorities) or privately run.

The work involves managing the movement of cargo containers between cargo ships, trucks and freight trains and optimizing the flow of goods through customs to minimize the amount of time a ship spends in port. Maintaining efficiency involves managing and upgrading gantry cranes, berths, waterways, roads, storage facilities, communication equipment, computer systems and dockworkers' union contracts. The port operator also manages paperwork, leases, safety and port security.

The Linux kernel is a free and open-source Unix-like kernel that is used in many computer systems worldwide. The kernel was created by Linus Torvalds in 1991 and was soon adopted as the kernel for the GNU operating system (OS) which was created to be a free replacement for Unix. Since the late 1990s, it has been included in many operating system distributions, many of which are called Linux. One such Linux kernel operating system is Android which is used in many mobile and embedded devices.

Most of the kernel code is written in C as supported by the GNU Compiler Collection (GCC) which has extensions beyond standard C. The code also contains assembly code for architecture-specific logic such as optimizing memory use and task execution. The kernel has a modular design such that modules can be integrated as software components – including dynamically loaded. The kernel is monolithic in an architectural sense since the entire OS kernel runs in kernel space.

A software system is a system of intercommunicating components based on software forming part of a computer system (a combination of hardware and software). It "consists of a number of separate programs, configuration files, which are used to set up these programs, system documentation, which describes the structure of the system, and user documentation, which explains how to use the system".

A software system differs from a computer program or software. While a computer program is generally a set of instructions (source, or object code) that perform a specific task, a software system is more or an encompassing concept with many more components such as specification, test results, end-user documentation, maintenance records, etc.

In computing, a legacy system is an old method, technology, computer system, or application program, "of, relating to, or being a previous or outdated computer system", yet still in use. Often referencing a system as "legacy" means that it paved the way for the standards that would follow it. This can also imply that the system is out of date or in need of replacement.

Legacy code is old computer source code that is no longer supported on standard hardware and environments, and is a codebase that is in some respect obsolete or supporting something obsolete. Legacy code may be written in programming languages, use frameworks and external libraries, or use architecture and patterns that are no longer considered modern, increasing the mental burden and ramp-up time for software engineers who work on the codebase. Legacy code may have zero or insufficient automated tests, making refactoring dangerous and likely to introduce bugs. Long-lived code is susceptible to software rot, where changes to the runtime environment, or surrounding software or hardware may require maintenance or emulation of some kind to keep working. Legacy code may be present to support legacy hardware, a separate legacy system, or a legacy customer using an old feature or software version.

Distributed computing is a field of computer science that studies distributed systems, defined as computer systems whose inter-communicating components are located on different networked computers.

The components of a distributed system communicate and coordinate their actions by passing messages to one another in order to achieve a common goal. Three challenges of distributed systems are: maintaining concurrency of components, overcoming the lack of a global clock, and managing the independent failure of components. When a component of one system fails, the entire system does not fail. Examples of distributed systems vary from SOA-based systems to microservices to massively multiplayer online games to peer-to-peer applications. Distributed systems cost more than monolithic architectures, primarily due to increased needs for additional hardware, servers, gateways, firewalls, new subnets, proxies, and so on. Distributed systems can also suffer from fallacies of distributed computing. Conversely, a well-designed distributed system is more scalable, more durable, more changeable, and more fine-tuned than a monolithic application deployed on a single machine. According to Marc Brooker: "a system is scalable in the range where marginal cost of additional workload is nearly constant." Serverless technologies fit this definition but the total cost of ownership, and not just the infra cost must be considered.

A package manager or package management system is software that supports installing, upgrading, configuring, and removing software for the host system in a consistent manner.

A package manager deals with packages, distributions of software and data in archive files. Packages contain metadata, such as the software's name, description of its purpose, version number, vendor, checksum (usually a cryptographic hash function), and a list of dependencies necessary for the software to run properly. Upon installation, metadata is stored in a local package database. Package managers typically maintain a database of software dependencies and version information to prevent software mismatches and missing prerequisites. They work closely with software repositories, binary repository managers, and app stores.

Binary-code compatibility (binary compatible or object-code compatible) is a property of a computer system, meaning that it can run the same executable code, typically machine code for a general-purpose computer central processing unit (CPU), that another computer system can run. Source-code compatibility, on the other hand, means that recompilation or interpretation is necessary before the program can be run on the compatible system.

For a compiled program on a general operating system, binary compatibility often implies that not only the CPUs (instruction sets) of the two computers are binary compatible, but also that interfaces and behaviours of the operating system (OS) and application programming interfaces (APIs), and the application binary interfaces (ABIs) corresponding to those APIs, are sufficiently equal, i.e. "compatible".

A syntax error is a mismatch in the syntax of data input to a computer system that requires a specific syntax. For source code in a programming language, a compiler detects syntax errors before the software is run (at compile-time), whereas an interpreter detects syntax errors at run-time. A syntax error can occur based on syntax rules other than those defined by a programming language. For example, typing an invalid equation into a calculator (an interpreter) is a syntax error.

Some errors that occur during the translation of source code may be considered syntax errors by some but not by others. For example, some say that an uninitialized variable in Java is a syntax error, but others disagree – classifying it as a static semantic error.

In computer security, logging in (or logging on, signing in, or signing on) is the process by which an individual gains access to a computer system or program by identifying and authenticating themselves.

Typically, user credentials consist of a username and a password. These credentials themselves are sometimes referred to as a login. Modern secure systems often require a second factor, such as email or SMS confirmation for extra security. Social login allows a user to use an existing cell phone number or user credentials from another email or social networking service to sign in or create an account on a new website.