PRC (Palm OS)

PRC (Palm Resource Code) is a container format for code databases in Palm OS, Garnet OS and Access Linux Platform. Its structure is similar to PDB databases.[1] Usually, a PRC file is a flat representation of a Palm OS application that is stored as forked database^[clarification needed] on the PDA.

PRC files are also used by the Mobipocket e-book-reader (here sometimes referred to as MOBI format[2]). The AZW format of Amazon's Kindle reading device is in turn a DRM-restricted form of the Mobipocket format.

On Palm OS, PRC files are used for applications, localized resources (overlays) and shared libraries.[1]

Structure of PRC file

In its essence, a PRC file is similar to a classic Mac OS application. It contains a PRC header, PRC resource headers and PRC resources.[3]

PRC Header

PRC Resource Header

PRC Resources

PRC Header

The PRC header is located at the beginning of the file and contains meta-information on the file:[3]

Offset	Name	Type	Size
0x00	name	char	32 Bytes
0x20	flags	integer	2 Bytes
0x22	version	integer	2 Bytes
0x24	creation time	32bit integer - PDB Datetime	4 Bytes
0x28	modification time	32bit integer - PDB Datetime	4 Bytes
0x2c	backup time	32bit integer - PDB Datetime	4 Bytes
0x30	mod_num	integer	4 Bytes
0x34	app_info	integer	4 Bytes
0x38	sort_info	integer	4 Bytes
0x3c	type	integer	4 Bytes
0x40	creator	integer	4 Bytes
0x44	unique_id_seed	integer	4 Bytes
0x48	next_record_list	integer	4 Bytes
0x4c	num_records	integer	2 Bytes

PRC Resource Header

For every resource (specified by num_records), there is a resource header containing:[3]

name	type	notes	size
name	char	Name of the resource	4 bytes
ID	integer	ID number of the resource	2 bytes
offset	integer	Pointer to resource data	4 bytes

PRC Resources

Every application contains al least a Code #0 resource with size information and jump tables, a Code #1 resource with executable code and data resources containing pre-initialized values of global variables in compressed form.[3] Other resources that may be contained are forms, form objects, alerts and multimedia data, e. g. images and sounds.

References

1. N. Rhodes, J. McKeehan. Palm OS Programming, Second Edition, O'Reilly, 2001, ISBN 1-56592-856-3.
2. MobileRead Wiki: Reference for the MOBI format
3. Theodore Ts'o (2000) The PRC Format. Accessed on 2009-03-07