Single File System: Virtual File System Delphi Library
for Archive / Backup with Transparent Compression and Strong Encryption
Compression algorithms
Single File System (SFS) provides 3 main compression algorithms:
·  ZLIB algorithm (InfoZip, http://www.infozip.org/)

·  BZIP algorithm (by Julian Seward, jseward@acm.org.)

·  PPM algorithm, variant G (by Dmitry Shkarin, shkarin@arstel.ru)

SFS has 3 levels for each of above algorithms: Fastest, Normal and Max.
Level Meaning
sfsNone No compression
zlibFastest ZLib algorithm, Fastest compression
zlibNormal ZLib algorithm, Normal balance between speed and compression rate
zlibMax ZLib algorithm, Maximum compression, rather slow speed
ppmFastest PPM algorithm, Fastest compression
ppmNormal PPM algorithm, Normal balance between speed and compression rate
ppmMax PPM algorithm, Maximum compression, rather slow speed
bzipFastest BZIP algorithm, Fastest compression
bzipNormal BZIP algorithm, Normal balance between speed and compression rate
bzipMax BZIP algorithm, Maximum compression, rather slow speed
Typically ZLib is the fastest algorithm, BZIP is fast and has a good rate, PPM provides the maximum rate with rather low speed.
But it also depends on compression level: i.e. for some files bzipNormal could give you both better compression rate and higher speed than zlibMax.
So we strongly recommend you to test the above compression levels with your application data, to make an optimal choice.
The most advanced users of SFS editions with source code could also tune the parameters of compression algorithms to achieve the best result for their specific tasks.
Encryption algorithm
Password protection is provided by the Rijndael encryption algorithm (AES), 256 bit key.
