Cognitive Scaffold

Preparing your thinking workspace

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MENTAL MODEL · M0181

The Busy Beaver

The Busy Beaver
SystemsHigh supportSystems Theory
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Version 1.0.0 · Updated 2026-07-28

CORE DEFINITION

In computer science, the Busy Beaver is a terminating program that, given a parameter, seeks the maximum possible output. The Busy Beaver game involves designing a terminating Turing machine that outputs only 0 or 1, aiming to output as many 1s as possible on a tape. The two-state Busy Beaver game has the following two rules: The Turing machine includes two states in addition to the halt state. The tape is initially all zeros. The player must design a state transition table that outputs the maximum number of 1s while also ensuring the machine terminates. A Turing machine that wins the n-state Busy Beaver game is called the nth Busy Beaver, denoted BB-n (BB stands for Busy Beaver). BB-n is the machine among all n-state Turing machines that outputs the most 1s. For example, BB-2 can output 4 ones in 6 state transitions. The Busy Beaver game was proposed by Hungarian mathematician Tibor Radó in his 1962 paper 'On Non-Computable Functions'.

SCAFFOLDING EFFECT

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Reduce cognitive load

In computer science, the Busy Beaver is a terminating program that, given a parameter, seeks the maximum possible output. The Busy Beaver game involves designing a terminating Turing machine that outputs only 0 or 1, aiming to output as many 1s as possible on a tape. The two-state Busy Beaver game has the following two rules: The Turing machine includes two states in addition to the halt state. The tape is initially all zeros. The player must design a state transition table that outputs the maximum number of 1s while also ensuring the machine terminates.

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Anchor fast decisions

The Busy Beaver problem: among Turing machines with a given number of states, find the machine that writes the most 1s (or takes the most steps) before halting. Its function grows faster than any computable function, revealing the boundaries of computability and the unsolvability of the halting problem.

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    zh.wikipedia.orghttps://zh.wikipedia.org/wiki/%E5%BF%99%E7%A2%8C%E7%9A%84%E6%B5%B7%E7%8B%B8ZH · Explicit
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