A standard partly created by ACR-NEMA in conjunction with various vendors. It defines the structure of an image in terms of its headers and the image component. We do not need to actually understand the technicalities of this. The images are usually saved as .dcm images. Some of the earlier machines may have some of these, but not all.
Wireless connections are also now possible.
There are many reasons for this. We need engineers from the modality vendor to enter the service mode. Some companies have extremely user-unfriendly interfaces and it makes sense to have the company engineers around. It is advisable to buy a new workstation computer rather than to upgrade from an old one. The type of computer will depend on your needs.