I want to know this, because I deleted some ncf/gcf files for portal 2, because the updating was stuck. And now it wants to download it all (11GB) again, so it would be nice if I could copy the content to the download location, without Steam noticing.

  • Aren't you worried about file corruption that might cause Steam to choke again, resulting in all 11 GB having to be redownloaded anyway?
    – BoltClock
    Jul 6, 2011 at 2:36
  • @The Annoying Pyro: Even if some files are corrupted, Steam won't have to download all of them. The new format (NCF) which is used for all newer games including Portal 2 is able to download indiviual files instead of whole packs (GCF).
    – Koraktor
    Jul 6, 2011 at 7:51

2 Answers 2


I would let Steam download whatever it wants to right now and reach a stable point.

(or you could rollback from your Time Machine backup).

When you have something that works, then consider asking Steam to back up your files to external media so you have working files next time you want to restore something.


Game files are stored in ~/Library/Application Support/Steam/SteamApps (NCFs and GCFs) and ~/Library/Application Support/Steam/SteamApps/common (for files extracted from GCFs or referenced by NCFs).

Copying and pasting files there might work as expected but - as "The Annoying Pyro" mentions above - is prone to (existing) file corruption. So I would recommend the following procedure:

  1. Copy the files in place
  2. Let Steam download missing files
  3. Let Steam check file consistency (and download corrupt ones again)

Please note that this might not work as well as I might look in the first place. Steam might want to download all files again when it thinks they are corrupt. But it's worth a try.

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