Activation Record

An activation record, also known as a stack frame, is a data structure that stores information about a particular function or procedure during its execution. It contains various components that are necessary for the execution of the function, such as local variables, return address, parameters, and control links.

Access Link

The access link is a component of the activation record that points to the activation record of the calling function or procedure. It is used to access non-local data stored in other activation records.

Non-Local Data

Non-local data refers to variables or data that are not directly accessible within the current function or procedure but are stored in other activation records. These variables are typically defined in the calling function or in a higher-level scope.

Explanation

In the given options, the access link (option B) is the activation record unit that points to non-local data stored in other activation records. This is because the access link is used to maintain a link to the activation record of the calling function or procedure.

When a function or procedure is called, a new activation record is created and pushed onto the call stack. The access link of the new activation record is set to point to the activation record of the calling function. This allows the current function to access variables or data defined in the calling function or in higher-level scopes.

By following the access link chain, a function can access non-local data stored in other activation records. This is particularly useful in situations where a function needs to access variables or data that are not directly accessible within its own activation record.

To summarize, the access link in an activation record is responsible for maintaining a link to the activation record of the calling function or procedure, allowing access to non-local data stored in other activation records.