Palm Digital Media, the e-book division of PalmSource, announced that the stock of its online e-library has increased from 3,500 in June 2002 to 10000. All Palm digital media e-books are designed to be read only on PalmSource's own PalmReader program, which can run on Palm OS devices, Pocket PC, Macintosh and Windows PC. Palm reading is an e-book format, which is proprietary to readers and encrypted by so-called digital rights management (DRM). DRM system encrypts computer files, and only specific programs can decrypt and access these files. Conversely, the program has the function of simplifying settings, which can prevent users from taking some actions on files, such as copying between systems. The file also usually matches the unique decryption code of a specific device. Large copyright agencies believe that without this mechanism, they will not be able to make a profit in electronic media sales. Other formats, including Microsoft reader and Adobe e-book format, all use DRM system, but they are not as popular as palm reading format. All DRM formats compete for unencrypted "open" formats, such as the widely circulated PalmDoc.