Instructions on how to download, install, compile, and run L-Galaxies 2020 on different operating systems are here:
On Linux

On Mac OS

On Windows

Note that the minimum storage requirment to run a minimal working version of L-Galaxies 2020 is ~3.5 GB (including the output file generated). For more information on L-Galaxies storage requirements, see below.

Storage requirements
For a basic L-Galaxies 2020 installation, (a) code files, (b) some dark matter merger-tree files (i.e. "treefiles"), and (c) some spectrophotometric tables are needed. In most cases, only a handful of treefiles are required to return a representative sub-volume containing a realistic range of galaxies (i.e. to roughly reproduce the observed stellar mass function at z=0). The total storage space requirements for these basic files are:

When run on Millennium-I:
Minimum: ~2.5 GB (to run on treefile 5)
Typical: ~9.2 GB (to run on treefiles 0-9)
Maximum: ~402.2 GB (to run on the full Millennium-I, 512 treefiles)

When run on Millennium-II:
Minimum: ~2.0 GB (to run on a single treefile - WARNING: not a representative sub-volume)
Typical: ~6.3 GB (to run on treefiles 40-79)
Maximum: ~186.7 GB (to run on the full Millennium-II, 512 treefiles)

Note that the above estimates do not include the space required to store newly-generated output files. The sizes of these can vary greatly, depending on the number of treefiles used, whether "snapshot" or "galaxytree" mode is chosen, and (in the snapshot mode case) which redshift is outputted. A rough guide to the typical size of each output file for the L-Galaxies 2020 "Default Model" is provided here (for the full set of output files from the whole simulation, multiply by 512):

Outputs when run on Millennium-I:
Snapshot mode: ~50 MB - 1.5 GB each
Galaxytree mode: ~10-25 GB each

Outputs when run on Millennium-II:
Snapshot mode: ~25-350 MB each (excluding treefile 0)
Galaxytree mode: ~10-25 GB each