Generally, these SSD drives contain the operating system and system files. They do not have to be restricted to that but these drives are small compared to 1 or 2 or 3 or 4 TB platter hard drives. And the larger the SSD drive the more expensive it gets. It is good for the OS as it boots fast and reads and writes fast. In the future they will get less expensive and we will then see multi TB SSD drives. With a desktop you will still want a large conventional hard drive to supplement the SSD drive for storage and software. That may not be as crucial on a laptop.