In terms of the scaling process, scale up is the traditional model to improve the power of the underlying system. As new resources are added in the same box, it is interpreted as vertical scaling. This is depicted in the following figure:

Let me explain this with a simple day-to-day example. On purchasing a personal laptop, the initial hard disk configuration might be 500 GB. After a while, the disk gets full and there is a pressing need to increase the volume of the hard disk. So, the next step might be to increase the volume of the existing hard disk capacity to, say, 1 TB.

Taking advantage of such resources is termed scaling up. This concept is applicable to any type of system resources, such as RAM, processor, disk storage, application, and so on.