First of all, I'd also like if this process has a proper name, I just named it the way I call it.

What I mean with 2-step installers is those installers that will make user download an (usually small) installer, then when user runs the installer, it downloads more content. For reference, think of most Google apps. For example I just downloaded Google Photos, which is a 1.1Mb file. Once you run that file, the real program is downloaded and installed.

While at first it looks nice to have the program you want to install downloaded in a few seconds, I think it's really frustrating to see that in fact you didn't download the program, but something else, and your real download is going to start AFTER that original download of the installer.

Thinking about the security side, if I gave permission to the installer as an admin, the newly downloaded stuff won't request for any additional permission, at least not with a normal configuration. I think this could be a HUGE security concern, but I'm not an expert on the subject, so really can't tell.

I know one of the most common reasons for this is to bundle unwanted software (SourceForge did this for some time, don't know now. Adobe Flash still does it, including McAfee unless you uncheck a box), but I know other software companies don't do it for this reason, yet they use the 2-step installer approach.

What's the rationale or purpose behind this? Are there any kind of technical, usability or security reasons for this?

EDIT: After installing Google Photos App on PC, now I see Google bundled unrequested software (specifically Google Docs, Google Sheets and Google Slides)

2 Answers 2


There are a number of reasons behind it

  1. Initial buy in : The small app size allows users to quickly buy into the experience of the app while downloading additional information in the background. If the user was required to download a large app to completely experience it, the chances of him installing or downloading the whole app drop significantly. I recommend looking at this article which shows how the increase in app sizes has a direct reduction in the the users actually downloading it

…and lose 66% of your installs

With the larger app sizes, we saw substantial losses in product page to app install rate. In particular, there was a substantial drop around the cellular download limit (~100MB), above which Apple does not let users download the app over 3G or 4G

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  1. Allow users to download the latest version of the app (with all the related files) : While this might not be specific to mobile devices, having an installer allows the software to ensure users are getting the latest and complete version from the official server. For example a search for the full chrome installer gives me multiple results from different sources.

enter image description here

Interestingly the top link is from AVG and not google and there is no indicator that it is the latest full version. However having a smaller installer ensures the system files are synced from the correct repository.

  1. Allow users to learn more about the product and also pitch the features of the product to them : The smaller size allows users to learn more about the product and what features they can use. It also gives a visual indicator of how the download is progressing and what the next stages are (rather than being stuck in a download loop)

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For example the firefox installer above informs the user of the current state but also informs him about what firefox can do.

It can also be used to do some preliminary validation checks such as system compatibility as shown below.

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  • 1
    The Effect of Mobile App Size on Downloads article is interesting - but there is a flaw in their methodology (as can be seen by some of the comments they copy from the app store) - people are making a comparative judgement, and if mortgage calculators are typically 3-5 MB, one that is 30+ MB will be penalised. Conversely, some other apps may benefit from apparently larger downloads - it infers more functionality, more content, or better content (for example, textures/graphics in a game). A better test would be a more complicated app that can be bloated artificially.
    – HorusKol
    Commented Aug 29, 2017 at 2:14

If I had to guess, I would say there are a couple advantages, although personally I hate the two-step shuffle.

  1. The user may be on a slow connection (at a library, etc.) and can get the first step quickly, and then do the actual install later.
  2. The vendors may want to avoid casual users from downloading huge setup programs that they might never end up using, wasting their bandwidth. They can also provide the latest version whenever the small install is ran; and the small install program can stay the same.

I think your assumption that it gives the users a perception that it downloads fast (but not overall really) that the program must be fast too is probably another reason. I don't see any security issues per se as a full download may also have useless toolbars etc. occasionally.

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