checkpoints

A checkpoint is a designated point in a process where verification, control, or a pause is imposed to ensure safety, accuracy, or progress. Checkpoints appear in many domains, from computing and biology to transportation and manufacturing.

In computing, checkpointing is the practice of saving the state of a program or system so it can be restored after a failure or interruption. Checkpoints enable fault tolerance in long-running computations, databases, and distributed systems. They may capture memory, processor state, and I/O progress, and can be full, incremental, or differential.

In biology, checkpoints monitor critical transitions in cellular processes. Cell cycle checkpoints—such as G1/S, G2/M, and the spindle assembly checkpoint—verify DNA integrity and proper chromosome alignment before progression. Failures can lead to mutations, while robust checkpoints preserve genomic stability. Immune checkpoints are regulatory pathways that modulate T cell activation to prevent autoimmunity. Blockade of these checkpoints with monoclonal antibodies, such as anti-PD-1 or anti-CTLA-4 therapies, can enhance anti-tumor responses in cancer treatment.

In travel and security, checkpoints are locations where documents or cargo are inspected, such as border crossings, airport security checkpoints, or vehicle checkpoints. They serve to enforce laws, assess risk, and manage the flow of people and goods.

In management and manufacturing, quality or milestone checkpoints are predefined evaluations used to verify requirements, allocate resources, and decide whether to continue, pause, or halt a project. Checkpoints thus function as mechanisms to constrain risk and guide progress across diverse systems.