Chapter 2. Resource Files

with significant contributions from Petr Vyhnak and Vladimir Gneushev

In order to allow games to be both distributeable and playable from several floppy disks, SCI was designed to support multi-volume data. The data itself could therefore be spread into separate files, with some of the more common resources present in more than one of them. The global index for these files was a "resource.map" file, which was read during startup and present on the same disk as the interpreter itself. This file contained a linear lookup table that mapped resource type/number tuples to a set of resource number/ offset tuples, which they could subsequently be read from.
 

SCI0 Resources

resource.map

The SCI0 map file format is pretty simple: It consists of 6-byte entries, terminated by the sequence 0xffff ffff ffff. The first 2 bytes, interpreted as little endian 16 bit integer, encode resource type (high 5 bits) and number (low 11 bits). The next 4 bytes are a 32 bit LE integer that contains the resource file number in the high 6 bits, and the absolute offset within the file in the low 26 bits. SCI0 performs a linear search to find the resource; however, multiple entries may match the search, since resources may be present more than once (the inverse mapping is not injective).