NAS vendors manufacture NAS as:
Computer-based NAS
Some NAS devices are purpose-built computers with processors and operating systems. Although it may technically be possible to run other software on a NAS unit, a computer-based NAS is not designed to be a general-purpose server. For example, NAS units usually do not have a keyboard or display and are controlled and configured over the network.
Embedded system NAS
A full-featured operating system is not needed on a NAS device, so some NAS vendors embed a lightweight operating system directly in the hardware.
Integrated chip-based NAS
The lowest level NAS device uses an integrated microchip processor. It manages file server functions directly in the chip, with no operating system. These NAS devices are less common.