There are two resume formats that can be used for technical resumes — chronological and hybrid. IT hiring managers want to know what you did, for whom, and during what time frame, and they’re typically focused on the last 7-8 years of employment. They want to understand the technical environment in which you worked, including the size and complexity of the IT department. This means that functional resume formats that are designed to minimize any existing job and skills gaps are not a good choice for technical positions.
The reasoning behind this is that there are few industries that have changed as radically as technology, so describing an achievement in 2013 has a completely different technical and business context than something that was achieved years earlier. For those of us who remember Y2K, it was about bit sizes for storing dates; nowadays, we’re taking about the real-time analysis of big data with the velocity and volume of unstructured data in the gigabits.