At the scale the IRS is running, a copy of Windows is a few tens of dollars, which is about the cost of the necessary replacement keyboards over the lifespan of

At the scale the IRS is running, a copy of Windows is a few tens of dollars, which is about the cost of the necessary replacement keyboards over the lifespan of the computer. Ongoing patch support, however, is where MS actually shines here. Windows XP had support available for 13 years, with subsequent OSes being supported for 10+ years. In comparison, for OSes with support lengths as long as windows, like RHEL, the per-year support seat costs start at $49, which would lead to support costs of near $500 per seat over that same lifespan. So even with the IRS botching the rollout and needing to pay MS an extra year, they're still cheaper than the few Unix offerings that provide the duration of support MS does.