128K bytes of non-volatile configuration memory. K bytes of flash memory sized on embedded flash. Version Numbering Cisco uses a numbering scheme that uniquely identifies each release of the Cisco IOS software. Understanding this scheme will help you distinguish between the different types of releases that are available. Examples of major release numbers are 9.21, 10.0, 10.2, 11.1, and so on.
Maintenance releases are periodic revisions of major releases.
These are fully regression tested releases incorporating the most recent bug fixes. These numbers indicate that this version of software is an interim build.