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Round-robin (RR) es uno de los algoritmos empleados por los planificadores de procesos y de redes en informática​​. El algoritmo usa intervalos de tiempo (también conocidos como cuanto (quantum))​ que se asigna a cada proceso en proporciones iguales, en orden circular y sin prioridades entre procesos. Es un algoritmo simple y facil de implementar y libre de inanición (un proceso no consigue ejecutarse) además aunque es muy usado en los sistemas operativos para la planificación de procesos, también se puede usar para solucionar otros problemas de planificación como la de paquetes en redes informáticas.

A Round Robin preemptive scheduling example with quantum=3

Planificación de procesos

Para planificar procesos mediante round-robin el planificador le asignará a cada proceso un slot o cuanto de ejecución​, es decir el tiempo máximo que el proceso puede ejecutarse en CPU, si el proceso acaba el cuanto asinado es expulsado de la CPU y debe volver a esperar en la cola circular (generalmente implementada como una FIFO) antes de poder volver a ejecutarse. En caso de que el proceso termine su ejecución antes que su cuanto (o quede en estado de espera, por ejemplo por necesitar realizar una operación de entrada-salida) el planificador le permitirá entrar a CPU al siguiente proceso en la cola de listo. En ausencia de otros procesos listos para ser ejecutados se permite al proceso actual seguir en CPU aunque su cuanto se haya acabado y por otra parte, si el sistema trabaja con cuantos grandes esto favorecerá a los procesos que requieren largos procesos de ejecución sobre los de menor tiempo o que realizan muchas operaciones de entrada-salida debido a que cuando vuelvan a necesitar ejecutarse deberán volver al final de la cola de procesos listos aunque no hayan agotado su cuanto.

Round-robin algorithm is a pre-emptive algorithm as the scheduler forces the process out of the CPU once the time quota expires.

For example, if the time slot is 100 milliseconds, and job1 takes a total time of 250 ms to complete, the round-robin scheduler will suspend the job after 100 ms and give other jobs their time on the CPU. Once the other jobs have had their equal share (100 ms each), job1 will get another allocation of CPU time and the cycle will repeat. This process continues until the job finishes and needs no more time on the CPU.

• Job1 = Total time to complete 250 ms (quantum 100 ms).

1. First allocation = 100 ms.
2. Second allocation = 100 ms.
3. Third allocation = 100 ms but job1 self-terminates after 50 ms.
4. Total CPU time of job1 = 250 ms

Consider the following table with the arrival time and execute time of the process with the quantum time of 100 ms to understand the round-robin scheduling:

Process name	Arrival time	Execute time
P0	0	250
P1	50	170
P2	130	75
P3	190	100
P4	210	130
P5	350	50

Round Robin Scheduling

Another approach is to divide all processes into an equal number of timing quanta such that the quantum size is proportional to the size of the process. Hence, all processes end at the same time.

Network packet scheduling

In best-effort packet switching and other statistical multiplexing, round-robin scheduling can be used as an alternative to first-come first-served queuing.

A multiplexer, switch, or router that provides round-robin scheduling has a separate queue for every data flow, where a data flow may be identified by its source and destination address. The algorithm allows every active data flow that has data packets in the queue to take turns in transferring packets on a shared channel in a periodically repeated order. The scheduling is work-conserving, meaning that if one flow is out of packets, the next data flow will take its place. Hence, the scheduling tries to prevent link resources from going unused.

Round-robin scheduling results in max-min fairness if the data packets are equally sized, since the data flow that has waited the longest time is given scheduling priority. It may not be desirable if the size of the data packets varies widely from one job to another. A user that produces large packets would be favored over other users. In that case fair queuing would be preferable.

If guaranteed or differentiated quality of service is offered, and not only best-effort communication, deficit round-robin (DRR) scheduling, weighted round-robin (WRR) scheduling, or weighted fair queuing (WFQ) may be considered.

In multiple-access networks, where several terminals are connected to a shared physical medium, round-robin scheduling may be provided by token passing channel access schemes such as Token Ring, or by polling or resource reservation from a central control station.

In a centralized wireless packet radio network, where many stations share one frequency channel, a scheduling algorithm in a central base station may reserve time slots for the mobile stations in a round-robin fashion and provide fairness. However, if link adaptation is used, it will take a much longer time to transmit a certain amount of data to "expensive" users than to others since the channel conditions differ. It would be more efficient to wait with the transmission until the channel conditions are improved, or at least to give scheduling priority to less expensive users. Round-robin scheduling does not utilize this. Higher throughput and system spectrum efficiency may be achieved by channel-dependent scheduling, for example a proportionally fair algorithm, or maximum throughput scheduling. Note that the latter is characterized by undesirable scheduling starvation. This type of scheduling is one of the very basic algorithms for Operating Systems in computers which can be implemented through a circular queue data structure.

See also

• Multilevel queue

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Games

The Game Boy Advance Game Pak

With hardware performance comparable to the Super Nintendo Entertainment System, the Game Boy Advance represents progress for sprite-based technology. The system's library includes platformers, SNES-like role-playing video games, and games ported from various 8-bit and 16-bit systems of the previous generations. This includes the Super Mario Advance series, as well as the system's backward compatibility with all earlier Game Boy titles. While most GBA games employ 2D graphics, developers have ambitiously designed some 3D GBA games that push the limits of the hardware, including first-person shooters like a port of Doom , racing games like V-Rally 3, and even platformers, like Asterix & Obelix XXL.

Some cartridges are colored to resemble the game (usually for the Pokémon series; Pokémon Emerald, for example, being a clear emerald green). They are also compatible with Nintendo DS and DS Lite (but see the Reception section for limitations). Some Advance cartridges have built-in features, including rumble features (Drill Dozer),​ and solar sensors (Boktai).​

In Japan, the final game to have been released on the system is Final Fantasy VI Advance on November 30, 2006, which is also the final game published by Nintendo on the system.​ In North America, the last game for the system is Samurai Deeper Kyo, released on February 12, 2008. Lastly, in Europe, 2 Games in 1: Columns Crown & ChuChu Rocket! is the last game for the system (and also the last one released on the system overall), released on November 28, 2008. The Japan-only Rhythm Tengoku, the first game in what would eventually become known outside Japan as the Rhythm Heaven/Rhythm Paradise series, is the final first-party-developed game for the system, released on August 3, 2006.

Compatibility with other systems

Clockwise from left: A Game Boy Game Pak, a Game Boy Advance Game Pak, and a Nintendo DS Game Card. On the far right is a US nickel shown for scale.

An accessory for the GameCube, known as the Game Boy Player, was released in 2003 as the successor to the Super Game Boy peripheral for the Super Nintendo Entertainment System. The accessory allows Game Boy Advance games, as well as Game Boy and Game Boy Color games, to be played on the GameCube. However, some games may have compatibility issues due to certain features requiring extra hardware. For example, games with built-in motion sensors (such as Yoshi's Topsy-Turvy) would require players to manipulate the console itself.

The GBA is the last of the three Nintendo handheld systems to bear the Game Boy name, games developed for it are incompatible with older Game Boy systems, and each game's box carries a label indicating that the game is "not compatible with other Game Boy systems". However, games designed for older Game Boy systems are conversely compatible with the Game Boy Advance, with options to play such games on either their standard aspect ratios or a stretched fullscreen.

Game Boy Advance games are compatible with Nintendo DS models that support them with a dedicated GBA cartridge slot beneath the touch screen, (specifically the original model and the Nintendo DS Lite), although they do not support multiplayer or features involving the use of GBA accessories because they do not have the GBA's external peripheral port that these features require to function. The Nintendo DSi and Nintendo DSi XL do not have backward compatibility with the GBA and a few DS games that use the GBA slot.

Virtual Console

Véase también: Virtual Console

As part of an Ambassador Program for early adopters of the Nintendo 3DS system, ten Game Boy Advance games, along with ten Nintendo Entertainment System games, were made available free for players who bought a system before the price drop on August 12, 2011.​ Unlike the other Virtual Console games for the system, features such as the Home menu or save states are missing, since the games are running natively instead of in emulation. 3DS systems that have custom firmware installed can also install the ten available games available to Ambassador Program members. Many other Game Boy Advance games can also be played via custom firmware by injecting a different game into one of the released Game Boy Advance games.^{[cita requerida]} Satoru Iwata stated Game Boy Advance games will be available on the Wii U's Virtual Console sometime during April 2014.​ On April 3, 2014, the first of the announced GBA games, Advance Wars, Metroid Fusion, and Mario & Luigi: Superstar Saga, were released for the Wii U's Virtual Console.​ A Virtual Console library of Game Boy Advance games was launched for the Wii U console. Similar to the original DS and DS Lite, all of the Virtual Console releases are single-player only, as they do not emulate multiplayer features enabled by Game Link cables.