Sustainability of Digital Formats: Planning for Library of Congress Collections

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AOL Personal Filing Cabinet

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name AOL Personal Filing Cabinet

America Online's (AOL) Personal Filing Cabinet or PFC is a proprietary database file that stores data from the AOL Desktop Software application to a local user-defined location for offline use. Stored data in PFC files can include stored email messages from AOL Mail (but not attachments to email), Internet bookmarks or Favorites, Away Messages, Newsgroup Postings and preferences such as user language and other configuration data. Because email attachments are not stored along with the message and instead are stored as 64-bit encoding, they can not be opened manually.

Each Username or AOL account has its own PFC file in the Organize folder. Because the file storage is local to the computer and to the Username, the stored files are not accessible if using a different computer, signing into a different account or signing in as a guest on the local computer. AOL Version 9 introduced the option to save email to AOL servers instead of "Save to My PC" which would provide access when signing in from another computer or as a guest from the local computer. Nonetheless, users often export their PFC data out of AOL to other platforms to improve accessibility and usability.

There is no published specification for PFC files; informal documentation comes from work done by Franz v. Gordon in 2002 through a reverse-engineering process and now available through the Internet Archive. Bruce Tomlin created partial documentation for the MacOS version of PFC which differs from the Windows version explored by Gordon. This document focuses on the Windows version. According to Gordon, PFC database files start with a header that includes the magic number file signifier, followed by an index table that contains pointers to all the data within the PFC. Each line in the index table starts with 52 53 00 00 (“RS”) and describes, among other values, the content type of the stored data object to which it’s pointing. The data could be a folder (including a system folder) or other coded values to identify the content type as a Favorite (bookmarked URL), a file that's been prepared for download or completely downloaded, email messages written or received, address book, email signature or availability status information ("Buddy away","Buddy preferences" and "Buddy icons"). Email messages are prefaced with 52 53 5c 30 5c 30 (“RS\0\0”) and then split into several subrecords starting with "AOLH" and ending with "AOLF". These subrecords include fields for the date/time, to, cc, bcc, subject, reply to, recipient, date/time as well as a flag to indicate if the message originated from inside or outside AOL. Other flag (at offset 0x16) indicates if the email message read (value 0), has an attachment (value 1), self written (value 2) and if the message has an embedded picture (value 3). Since they are not stored with the message, the name (which cannot include special characters) and length of attachments are recorded along with its stored location which varies for each browser. AOL 8.0 or 9.0 introduced a new option to send an email message as plain text so a value was added to the PFC to indicate text formatting preference as HTML or plain text. Content types other than email have different specific sets of relevant fields in the index tables.

Production phase Archived middle state.

Local use Explanation of format description terms

LC experience or existing holdings The Manuscripts Division at the Library of Congress has received PFC files with personal papers collections that included AOL email data.
LC preference The Library of Congress has not yet expressed any format preference for email collections in its Recommended Formats Statement.

Sustainability factors Explanation of format description terms

Disclosure Format is closed and proprietary.
    Documentation There is no available specification document from AOL. Franz V. Gordon in 2002 reverse-engineered informal documentation about the technical structure of the format.

Highly adopted thanks to the AOL Desktop market share. According to the Comscore Media Metrix Multi-Platform, AOL had 174,791 million monthly users in 2015. Because of the reliance on access to local data store, users often export PFC files to other formats including MBOX, EML and PST. Software tools such as Emailchemy can migrate PFC files to other email formats.

    Licensing and patents PFC files are intended for use only with AOL Desktop software. The compilers of this resource have not identified specific patents related to this software's functionality but assume that AOL does have patents that would prevent replication of the full functionality of the software. Comments welcome.
Transparency According to Wilson, email messages from AOL version 7.00 and later are compressed via zlib, a lossless data-compression library. This inhibits keyword searching because the data needs to be decompressed before such actions. The PFC file itself is binary and therefore not human readable. Email attachments are stored as 64-bit encoding.  
Self-documentation PFC files are highly structured thanks to the index table which points to the address location of all data in both open and closed folders.
External dependencies Active use of the PFC format requires the AOL Desktop application. However a number of PFC viewer tools exist including pfcviewer and SysTools AOL PFC Viewer.
Technical protection considerations

According to Gordon, email messages received with AOL 7.0 are stored in the PFC in encrypted form.

Quality and functionality factors Explanation of format description terms

File type signifiers and format identifiers Explanation of format description terms

Tag Value Note
Filename extension pfc
According to Gordon, the .pfc extension may be used for "formerly stored folders" which the writers of this resource take to mean older versions of the PFC file. Most resources however report that it is more common for the PFC file not to have any extension. Comments welcome.
Filename extension See note.  Each Username has its own PFC file in the Organize folder and the filename is the Username with no extension.
Magic numbers Hex: 41 4F 4C 56 4D 31 30 30
From Gary Kessler's Signature File Table
Pronom PUID See note.  No PUID as of November 2018.
Wikidata Title ID Q25110402

Notes Explanation of format description terms

General In November 2018, AOL stated that there's a total file size limit of 25MB per email, which includes both incoming and outgoing messages as well as attachments.
History According to Bright Hub, the first release of AOL for DOS was February 1991 and by 1993, AOL introduced its own email addresses and a Windows version. Other milestone releases include AOL 2.0 for Windows 3.x in September 1994, AOL 3.0 for Windows 95 in June 1996, AOL 6.0 for Windows XP in September 2001, AOL 9.0 for Vista November 2006, and AOL 10.0 (AOL Desktop) in December 2007. AOL Gold debuted on April 10th, 2017 which includes new features including two step authentication, encryption of personal information stored in AOL Desktop software, server side storage of favorites as well as contacts and automatic updating of the software. AOL 10.0 for Mac was released in May 2008. The first recorded use of PFCs are in AOL 3.0 from 1996 but PFC may go back even earlier. Comments welcome.

Format specifications Explanation of format description terms

Useful references


Last Updated: 11/29/2018