PPM to TCR Converter

TCR (Text Compression for Reader) is a compressed plain-text ebook format developed by Barry Childress in the early 1990s for the Psion Series 3 family of palmtop computers. The format was created for Childress's Reader3 application, a text file viewer that needed to fit large books into the Psion's extremely limited storage — typically 128 KB to 2 MB of available memory. TCR uses a dictionary-based compression scheme derived from the earlier ZVR format by Ian Giddings, replacing repeated byte sequences with single-byte tokens that reference a header dictionary. This straightforward approach achieves compression ratios of roughly 40-60% on typical English prose while requiring minimal CPU resources for decompression. The Psion Series 3 ran on a 3.84 MHz NEC V30 processor with no floating-point unit, so TCR's low computational overhead was essential for smooth page-by-page reading. A key advantage is remarkable storage efficiency for its simplicity — users could carry dozens of novels on removable SSD cards that held only a few hundred kilobytes. The format found a dedicated user community among Psion enthusiasts who built libraries of compressed literature for portable reading years before smartphones existed. Though the Psion platform faded from the market in the early 2000s, TCR files can still be opened and converted by modern ebook tools, and the format stands as an early example of purpose-built mobile reading technology from the pre-smartphone era.