The market has been commenting on the rise of Juniper for some years and the fact that Cisco has not been able to stop them growing. Well, we can now see that Cisco was listening to the stock market by spending a lot of time and money developing a new operating system. Oh yeah, and some new hardware to run it on. Read all about the Cisco ASR 1000 here.
IOS performance limits
Its been clear for a long time that the conventional IOS had hit a wall in performance. The monolithic kernel has been subjected to any number of hacks to improve performance (fast switching, CEF) but ultimately, it obviously had to be discarded and a new approach built that supported modularity, improved upgrade, and other serviceability features. This has seen the release of NXOS (Nexus 7000), IOS XR (CRS-1) and now IOS XE for the ASR1000. You can probably also include IOS SX as used in C6500 and other switches as another.