Read-only memory for 3D
Read-only memory (ROM) is a class of storage medium used in computers and other electronic devices. Data stored in ROM can only be modified slowly, with difficulty, or not at all, so it is mainly used to distribute firmware (software that is very closely tied to specific hardware, and unlikely to need frequent updates).
Strictly, read-only memory refers to memory that is hard-wired, such as diode matrix and the later mask ROM. Although discrete circuits can be altered (in principle), Integrated Circuits (ICs) cannot and are useless if the data is bad. The fact that such memory can never be changed is a large drawback; more recently, ROM commonly refers to memory that is read-only in normal operation, while reserving the fact of some possible way to change it.