How does installer can download and install at the same time?


In mid 2000s, you usually must download the whole package first, then you can install it. But now, installer like chrome, steam, can download and install at the same time. How does it work?

In: Technology

The “installer” downloaded is just a small program that contacts a web host to download the rest of the software. One advantage this offers is that the installer packages distributed will never be out of date.

This may have to do with increasing complexity of modern CPUs. Older machines may have only a single core CPU, while modern machines may have up to 64 cores per CPU. A single core CPU can only do 1 thing at a time, such as download a program or install said program. Multi-core CPUs can do both at the same time.

A useful analogy to consider is that of a builder constructing a wall. The builder needs to get bricks from the store (downloading), and then build the wall (install). Having a single worker (CPU core) means that they can only go to the store to get bricks or build the wall at any one time. Having more than 1 means that one worker can go to the store while the second builds the wall.

Usually the thing you want to install is split up into separate files. They just download one (or a few files) and then extract and/or install.

Simple old-style installers would basically be a fancy ZIP archive that could copy files to multiple locations and make a few modifications to system files. That’s right, the entire program was contained within the install.exe in compressed form. So, you would have to download the entire thing before beginning the install process.

Modern installers replace the ZIP-archive-like part with commands to download files directly from the developer’s server, allowing the install.exe to be much smaller so that you can begin the process sooner.