Because the new VPK files are independent of distribution (Left 4 Dead is distributed by NCF files and Steam knows nothing of the VPK file format), their content is split up over multiple archives that seem to be limited to about 32 MB in size. This meant that new and updated files could be efficiently downloaded and saved with minimal bandwidth and disk IO. Previous Source engine games that had been distributed by the more advanced GCF file format had the luxury of internally fragmenting new and updated files. In practice, this seems to be limited to the first 1000 bytes of Source engine materials ( VMT files) which are typically only a few hundred bytes in size. In order to efficiently access small or critical files, the beginning of each file can optionally be stored in the VPK directory. The solution was the conception of the VPK file format which is used to store Left 4 Dead materials, models and particles in a handful of files which can be quickly accessed. Source engine materials and models are stored in thousands of small files and it would be expensive to continuously open and close these files. Possibly brought on by poor performance, the NCF file format was introduced and all game content was copied entirely to the hard drive. configuration files) and custom content were copied and stored locally on the user's hard drive. Prior to Left 4 Dead, typical Source engine games stored their content in GCF files.

How to install left 4 dead 2 vpk files