The back had a then-massive 16MB of RAM to act as an image buffer, as well as a PCMCIA card slot for image storage, plus a SCSI socket for connection to a computer. The imaging element was an APS-C sensor with a 1.5x crop factor, and a resolution of 1268 x 1012 pixels (1.3 mp). The camera back did not have an LCD monitor.
A typical 260MB PCMCIA card or IBM Microdrive of the period could store 189 images. The EOS DCS 3 lacked any internal JPEG processing, and images had to be processed on a computer before they were usable in any form. The large amount of memory contributed the then-immense price of the EOS DCS 3, at nearly two million yen.