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Zero wait state is a feature of a processor or computer architecture in which the processor does not have to wait to perform memory access.
Non-zero wait state describes the situation when a processor operates at a higher frequency than the memory, it has a wait state during which the processor is idle.
In computing, multitasking is the concurrent execution of multiple tasks over a certain period of time. New tasks can interrupt already started ones before they finish, instead of waiting for them to end. As a result, a computer executes segments of multiple tasks in an interleaved manner, while the tasks share common processing resources such as central processing units (CPUs) and main memory. Multitasking automatically interrupts the running program, saving its state and loading the saved state of another program and transferring control to it. This "context switch" may be initiated at fixed time intervals, or the running program may be coded to signal to the supervisory software when it can be interrupted.
An operating system (OS) is system software that manages computer hardware and software resources, and provides common services for computer programs.
On Unix and Unix-like computer operating systems, a zombie process or defunct process is a process that has completed execution but still has an entry in the process table: it is a process in the "terminated state". This occurs for the child processes, where the entry is still needed to allow the parent process to read its child's exit status: once the exit status is read via the wait system call, the zombie's entry is removed from the process table and it is said to be "reaped". A child process initially becomes a zombie, only then being removed from the resource table. Under normal system operation, zombies are immediately waited on by their parent and then reaped by the system. Processes that stay zombies for a long time are usually an error and can cause a resource leak. Generally, the only kernel resource they occupy is the process table entry, their process ID. However, zombies can also hold buffers open, consuming memory. Zombies can hold handles to file descriptors, which prevents the space for those files from being available to the filesystem. This effect can be seen by a difference between du and df. While du may show a large amount of free disk space, df will show a full partition. If the zombies are not cleaned, this can fill the root partition and crash the system.
In computing, a process is the instance of a computer program that is being executed by one or many threads. There are many different process models, some of which are light weight, but almost all processes are rooted in an operating system (OS) process which comprises the program code, assigned system resources, physical and logical access permissions, and data structures to initiate, control and coordinate execution activity. Depending on the OS, a process may be made up of multiple threads of execution that execute instructions concurrently.
In software engineering, a spinlock is a lock that causes a thread trying to acquire it to simply wait in a loop ("spin") while repeatedly checking whether the lock is available. Since the thread remains active but is not performing a useful task, the use of such a lock is a kind of busy waiting. Once acquired, spinlocks will usually be held until they are explicitly released, although in some implementations they may be automatically released if the thread being waited on blocks or "goes to sleep".
Peterson's algorithm is a concurrent programming algorithm for mutual exclusion that allows two or more processes to share a single-use resource without conflict, using only shared memory for communication. It was formulated by Gary L. Peterson in 1981. While Peterson's original formulation worked with only two processes, the algorithm can be generalized for more than two.
A wait state is a delay experienced by a computer processor when accessing external memory or another device that is slow to respond.
In computer science, the test-and-set instruction is an instruction used to write (set) 1 to a memory location and return its old value as a single atomic operation. The caller can then "test" the result to see if the state was changed by the call. If multiple processes may access the same memory location, and if a process is currently performing a test-and-set, no other process may begin another test-and-set until the first process's test-and-set is finished. A central processing unit (CPU) may use a test-and-set instruction offered by another electronic component, such as dual-port RAM; a CPU itself may also offer a test-and-set instruction.
The x86 instruction set refers to the set of instructions that x86-compatible microprocessors support. The instructions are usually part of an executable program, often stored as a computer file and executed on the processor.
A process control block (PCB), also sometimes called a process descriptor, is a data structure used by a computer operating system to store all the information about a process.
The MCP is the operating system of the Burroughs B5000/B5500/B5700 and the B6500 and successors, including the Unisys Clearpath/MCP systems.
The Zilog eZ80 is an 8-bit microprocessor designed by Zilog as an updated version of the company's first product, the highly-successful Zilog Z80. The eZ80 is binary compatible with the Z80, but operating almost three times faster at the same clock frequency.
The Western Design Center (WDC) 65C02 microprocessor is an enhanced CMOS version of the popular nMOS-based 8-bit MOS Technology 6502. It uses less power than the original 6502, fixes several problems, and adds new instructions. The power usage is on the order of 10 to 20 times less than the original 6502 running at the same speed; its reduced power consumption has made it useful in portable computer roles and industrial microcontroller systems. The 65C02 has also been used in some home computers, as well as in embedded applications, including medical-grade implanted devices.
Lamport's bakery algorithm is a computer algorithm devised by computer scientist Leslie Lamport, as part of his long study of the formal correctness of concurrent systems, which is intended to improve the safety in the usage of shared resources among multiple threads by means of mutual exclusion.
In computer science, a data buffer is a region of memory used to store data temporarily while it is being moved from one place to another. Typically, the data is stored in a buffer as it is retrieved from an input device or just before it is sent to an output device ; however, a buffer may be used when data is moved between processes within a computer, comparable to buffers in telecommunication. Buffers can be implemented in a fixed memory location in hardware or by using a virtual data buffer in software that points at a location in the physical memory.
Sun-1 was the first generation of UNIX computer workstations and servers produced by Sun Microsystems, launched in May 1982. These were based on a CPU board designed by Andy Bechtolsheim while he was a graduate student at Stanford University and funded by DARPA. The Sun-1 systems ran SunOS 0.9, a port of UniSoft's UniPlus V7 port of Seventh Edition UNIX to the Motorola 68000 microprocessor, with no window system. Affixed to the case of early Sun-1 workstations and servers is a red bas relief emblem with the word SUN spelled using only symbols shaped like the letter U. This is the original Sun logo, rather than the more familiar purple diamond shape used later.
In computer science, synchronization is the task of coordinating multiple processes to join up or handshake at a certain point, in order to reach an agreement or commit to a certain sequence of action.
A process is a program in execution, and an integral part of any modern-day operating system (OS). 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. To meet these requirements, The OS must maintain a data structure for each process, which describes the state and resource ownership of that process, and which enables the operating system to exert control over each process.
The Mitsubishi 740, also known as MELPS 740, is a series of 8-bit CMOS microcontrollers and microprocessors with an enhanced MOS Technology 6502 compatible core based on the expanded WDC 65C02. The ICs were manufactured by Mitsubishi Electric during the 1980s and 1990s.
AArch64 or ARM64 is the 64-bit Execution state of the ARM architecture family. It was first introduced with the Armv8-A architecture, and has had many extension updates.
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