We can distinguish between a number of ways in which modern technology can help historians:

1. information technology helps historians analyse millions of documents with much greater ease. This reduces the amount of bias in which documents we find important, because it is easier to step outside of the known and well-studied documents which previous historians have highlighted. The most obvious application of IT are digital databases and digitized records, preferably with the possibility of computationally searching through them for keywords.

Some people do something more complicated, using computer algorithms to analyse thousands of records to find patterns and relationships that are nearly impossible to find manually.

2. forensics and archaeology make it possible to analyse DNA to determine migration, heritage and family relationships. It also helps with determining how people lived and why they died. It happens quite often that people excavate some historical figure to run some tests on them, in the hope that modern science will answer some century old questions: did Tycho Brahe get poisoned? Where did Richard III get buried? How did Tutankhamun die?

3. Physics and Chemistry There are several techniques to measure the age of documents, artefacts or biological material. Also, we can accurately determine the composition of materials which can help us understand where they came from and how they were produced. We are also able to put stuff in scanners to look inside them and understand their structure without breaking things, and we even have ground scanners to see what's buried somewhere without having to dig. Furthermore, there are very nice methods to analyse damaged documents to figure out what was written on it, using special multi-spectrum lights and cameras that reveal otherwise invisible markings on the documents. This is also used to study pieces of art, to look underneath the paint and see what was drawn beneath it.

Perhaps as a questionable fourth category, we can add computational simulations and real-life experiments. These are used to test the validity of historical claims, as it allows you to see what some person hundreds of years ago might have seen. It's not always possible to replicate an experiment in real life (costs, impossible to reproduce situations, etc.), so computers can help a lot. For example, we can simulate how bright a supernova would have been for observers in 1572, or the position of Jupiter's moons at the time of Galileo's observations.