With the launch of the Palm III series version 3.0 of the OS was introduced. Incremental upgrades occurred with the release of versions 3.1, 3.3 and 3.5, adding support for colour, multiple expansion ports, new processors and other various additions.
A PalmOne m130 running OS 4.1
Version 4.0 was released with the m500 series, and later made available as an upgrade for older devices. This added a standard interface for external FS access (such as SD cards) and improved telephony libraries, security and UI improvements.
Version 5.0 was the first version released to support ARM devices. Described as a stepping stone to full ARM support, Palm apps are run in a emulated environment called PACE, decreasing speed but allowing great compatibility with old programs. New software can take advantage of the ARM processors with ARMlets, small units of ARM code. It was also roughly this time when Palm began to separate its hardware and OS efforts, eventually becoming two companies, PalmSource, Inc (OS) and PalmOne, Inc (hardware). Further releases of PalmOS 5 have seen a standardised API for hi-res and dynamic input areas, along with a number of more minor improvements.
Palm OS 5.2 and 4.2 (and later) also feature Graffiti 2, due to the loss of a patent infringement lawsuit with Xerox. This is based on Jot by CIC.
PalmSource, Inc released Palm OS 6.0 (also known as Palm OS Cobalt) to licencees on December 29th, 2003. This is to be the completion of the migration to ARM devices, and allow ARM native applications along with improved multimedia support.