GEOS Extensions

Later on in the life of the C64, the GEOS OS came out. It was a system much like many other windowing OS's (MAC OS, Windows) in that it used icons, windows, a mouse pointer and resource drivers. In order to contain all the information needed for the windowing system (icon, window position, creation time/date), a new filetype called VLIR was needed and directory changes were made. While GEOS files might not be of interest to many of the emulator users, it is likely that these files will be encountered, and knowledge of them would be helpful.

There are actually two types of GEOS files, VLIR and SEQuential. Don't confuse the GEOS SEQuential type with that of the standard D64 SEQ file. They are related, but not the same. VLIR are described in more detail following this paragraph. GEOS SEQuential files are all non-VLIR files, including normal PRG, USR and SEQ types.

GEOS files usually have an entity attached called an INFO block. It contains ICON info, author, file description, load address etc. However, just because an INFO block does not exist for a given file, does not mean that the file is not a GEOS file.

Each GEOS VLIR file or application is comprised of many separate chains (called RECORDS) for different sections of the app/file. Each RECORD can be loaded in separately and overtop of other ones. Below is a dump of the first directory sector of the GEOS 2.0 disk. Note the first entry seems normal enough, but the rest have additional information in the normally unused section of the entry.

The CBM File Type, GEOS file type and GEOS file structure fields are duplicated in both structures

CBM DOS file type

REL files are not permitted with GEOS. If byte 0x18 in the directory entry is 0x00 then it's a standard CBM DOS file, otherwise it's a GEOS file.

GEOS File type

File types 0x0F…0xFF are undefined.

Sources

• GEOS.TXT