There was a sore point with the 6600 operating system support — slipping timelines. The machines originally ran a very simple job-control system known as COS (Chippewa Operating System), which was quickly "thrown together" based on the earlier CDC 3000 operating system in order to have something running to test the systems for delivery. However the machines were intended to be delivered with a much more powerful system known as SIPROS (for Simultaneous Processing Operating System), which was being developed at the company's System Sciences Division in Los Angeles. Customers were impressed with SIPROS' feature list, and many had SIPROS written into their delivery contracts.