The first official USENIX conference was organized by Mel Ferentz at
CUNY in June 1975; it had approximately 40 attendees from 20 institutions. The conference evolved into a twice-yearly event, with one conference in summer and one in winter, and eventually grew to over 3,000 attendees. It had a strong practical bias and emphasized implementation; It came to be seen as a prestigious venue for systems research and received an 'A' rating from the CORE Conference Ranking system. This shift in focus was accompanied by a substantial decline in practitioner attendance. In parallel, a number of more specialized USENIX conferences emerged, such as
OSDI,
NSDI, FAST, and USENIX Security, some of which came to be regarded as more prestigious than ATC. Together, these developments contributed to ATC's declining attendance, from about 1,700 attendees in 2000 to about 300 in 2019. Although significantly smaller, attendance at that scale is generally considered reasonable and comparable to that of other academic systems research conferences, such as EuroSys. In 2020, ATC was held virtually due to the
COVID-19 pandemic. Since 2021, USENIX has co-located ATC with OSDI. Although attendees could freely move between the technical sessions of the two conferences and thus effectively attend both, USENIX required registrants to choose either ATC or OSDI on the online registration form. This either-or policy reduced the number of ATC registrants—not necessarily attendees—to 165 in 2024. The registration form also asked registrants whether they planned to attend both conferences, but USENIX did not publicize those numbers, so the actual number of attendees remains unknown. In 2025, USENIX declared the end of the conference series after 50 years of activity. Subsequently, members of the systems research community petitioned
ACM SIGOPS to step in and sponsor ATC instead; the petition was signed by a majority of the USENIX ATC steering committee members, along with hundreds of others, many of whom had authored ATC papers or served on ATC program committees. and ATC 2027 in France. Because the transition from USENIX to SIGOPS took time, ATC 2026 was scheduled with a June submission deadline and a November conference date. This is an exception: beginning with ATC 2027, the conference resumes its original submission deadline of January and its original conference date of July. ==Impact==