A basic assumption underlying short-term memory is that it is

limited in capacity

Explanation:

Short-term memory: The term short-term memory is a part of the information processing model, and is defined as one of the different stages that are responsible for memory storage.

It is responsible for holding yet not manipulating or altering a piece of information in an individual's mind in an active or readily present sate over the small duration.

The memory present in short-term memory is more or less for a few seconds.