PowerPC instead of IMPI, and for the operating system functionality previously implemented in the HLIC to be re-implemented elsewhere. This led to the HLIC and VLIC being replaced with a single layer named the System Licensed Internal Code (SLIC). The SLIC was implemented in an object-oriented style with over 2 million lines of C++ code, replacing some of the HLIC code, and most of the VLIC code. Owing to the amount of work needed to implement the SLIC, IBM Rochester hired several hundred C++ programmers for the project, who worked on the SLIC in parallel to new revisions of the VLIC for the CISC AS/400 systems. The first release of OS/400 to support PowerPC-based hardware was V3R6. Rebranding The AS/400 product line was rebranded multiple times throughout the 1990s and 2000s. As part of the 2004 rebranding to eServer i5, OS/400 was renamed to i5/OS; the 5 signifying the use of POWER5 processors. The first release of i5/OS, V5R3, was described by IBM as "a different name for the same operating system". In 2006, IBM rebranded the AS/400 line one last time to System i. In April 2008, IBM consolidated the System i with the System p platform to create IBM Power Systems. At the same time, i5/OS was renamed to IBM i, in order to remove the association with POWER5 processors. The two most recent versions of the operating system at that time, which had been released as i5/OS V5R4 and V6R1, were renamed to IBM i 5.4 and 6.1. Along with the rebranding to IBM i, IBM changed the versioning nomenclature for the operating system. Prior releases used a Version, Release, Modification scheme, e.g. V2R1M1. This was replaced with a Version.Release scheme, e.g. 6.1. Beginning with IBM i 7.1, IBM replaced the Modification releases with Technology Refreshes. Technology Refreshes are delivered as optional PTFs for specific releases of the operating system which add new functionality or hardware support to the operating system. Architecture When IBM i was first released as OS/400, it was split into two layers, the hardware-dependent System Licensed Internal Code (SLIC) and the hardware-independent Extended Control Program Facility (XPF). These are divided by a hardware abstraction layer called the Technology Independent Machine Interface (TIMI). Later versions of the operating system gained additional layers, including an AIX compatibility layer named Portable Application Solutions Environment (originally known as the Private Address Space Environment), and the Advanced 36