The system at Addenbrooke's and Rosie hospitals in Cambridge means nurses can access patient records on handheld devices instead of waiting for notes.
Addenbrooke's said it is the biggest patient care investment it has made.
Chief information officer Dr Afzal Chaudhry said patients should get medication quicker and leave sooner with the system in place.
The hospital is the first in the UK to use Epic's eHospital system, which is used in hospitals in the US.
The software currently contains more than 2.1m patient records from the last five years and it can be used on 7,000 computers and devices at the hospitals.
Nurses can quickly access and update patient records using 500 iPod Touch devices and using its barcode scanner, run tests such as measuring blood pressure.
The software can also be accessed on staff smartphones.
Last week the Cambridge News reported some staff were "panicking" and there was a "sense of doom" about the new system, which has required 200,000 hours of staff training.
A spokesman for Cambridge University Hospitals said no specific concerns had been highlighted up to chief executive level, but staff would be given 24-hour support.
It is expected to take a year until the system works entirely without paper.
Dr Chaudhry said: "It is the biggest single investment the Trust has ever made in the quality of patient care, and will make a real difference for everyone who comes into the Trust.
"Patients will get their medication quicker, nurses can spend more time with their patients and people who are treated here will get home sooner."
A £200m electronic patient record system that will eventually make two hospitals paperless has gone live.