nonwritable

Nonwritable refers to data, memory regions, or objects that cannot be modified after creation or initialization. In computing, nonwritable is often achieved through access control, immutable data structures, or hardware and software protections. The term is typically contrasted with writable or read-write data.

In storage and file systems, nonwritable data can be enforced by removing write permissions or mounting as read-only. Some systems offer an immutable flag (for example, Linux chattr +i) that prevents modification or deletion until the flag is removed, even by privileged users. Windows provides a read-only attribute on files, which can deter changes, though it is not always a guarantee against modification under all permission configurations.

In memory, nonwritable regions are enforced by the memory management unit and protection mechanisms such as the non-executable and non-writable pages. Write protections help prevent accidental or malicious modification of code and data. Policies like W^X (write or execute, not both) and executable space protections are part of this approach to enforce nonwritability where appropriate.

In software development, nonwritability is implemented through language features and design patterns. Languages often offer constants or read-only properties to prevent changes after initialization. For example, a non-writable property in JavaScript can be defined with writable: false, and many languages support immutable data structures or read-only attributes. Some languages also use const declarations to enforce non-writability of variables.

Nonwritable data improve stability, integrity, and security by reducing the risk of unintended or malicious modification. However, they can limit flexibility and complicate updates or maintenance, requiring deliberate steps to lift protections when changes are necessary.