# Knowledge Check: Why Containers Exist

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**1. What real problem does "it works on my machine" name?**

*Answer:* Dependency/environment inconsistency between where an application was developed and
where it actually needs to run — differences in libraries, versions, and configuration that are
easy to overlook and hard to fully document by hand.

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**2. What's the actual architectural difference between a container and a virtual machine, not
just "containers are smaller"?**

*Answer:* A container shares the host machine's kernel and only isolates the application's
process/filesystem/network view. A VM virtualizes an entire computer, including running its own
separate kernel — a genuinely different isolation model, not just a size difference.

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**3. Why do containers start so much faster than VMs?**

*Answer:* A container doesn't boot a separate operating system/kernel — it starts a process
using the ALREADY-RUNNING host kernel, while a VM has to boot an entire independent OS from
scratch.

## Instructor Notes

**Facilitation:** Question 2 is the one worth confirming explicitly — many students carry the
misconception "container = tiny VM" past this point without correction.

**Approximate timing:** 5 minutes.