Can a Wikipedia download be paused and resumed?

Yes. Wonder by Zaweba lets you pause a Wikipedia download, and the download survives closing Wonder altogether. When you start again it resumes from where it stopped rather than from the beginning, and when it finishes Wonder checks the file against the checksum Kiwix publishes.

That is important when an edition is big. The full English Wikipedia with pictures reaches 119 GB, and very few connections can bring that down in one sitting.

How resuming works

Downloads in Wonder come from Kiwix's servers and mirrors only. While a download runs, the part already fetched is kept as a .zim.part file along with a record of how far it has got. Pause it, close Wonder, shut the PC down for the night, and that file and record are still there in the morning.

When you carry on, Wonder asks the server for just the remaining part using HTTP range requests, the standard way of fetching a file from a given point. If one mirror is unavailable, it falls back to the next. You see the speed and time left as it goes.

Checks before and after

Before a download starts, Wonder checks you have enough free space for it, so you don't find out at 90 percent that the drive is full. At the end it verifies the whole file against Kiwix's SHA-256. A file that has been paused and resumed several times is checked just as carefully as one that came down in one go.

The download folder starts in your local app data. Because editions can reach 119 GB, you can change it, for example to a larger second drive.

Choosing an edition that fits your connection

Pausing is a help, but choosing the right edition helps more. Open File, then Library, and press Show what Kiwix offers. Each edition is listed with its size, date and article count before you download anything. Wikipedia in English comes as full with pictures, without pictures and introductions only, and the same three choices are offered for the top articles and for Simple English Wikipedia. Wiktionary and Wikivoyage are there as well.

On a slow or metered connection, an edition without pictures or with introductions only is far smaller, and still a remarkable thing to have offline. You can always add a bigger edition later.

Planning a big download

A sensible approach for a large edition is to start it when you can leave the computer on, pause it when you need the connection for something else, and let it carry on later. Because the download survives closing Wonder, there is no need to babysit it.

If you have a .zim file already, perhaps copied from another PC or downloaded earlier from Kiwix, you don't need to download it again. Press Ctrl+O and open it directly. Wonder reads ZIM files with its own reader and opens even a 119 GB edition in milliseconds.

Once it's done

The moment an edition is on your PC, Wonder needs no internet for reading, wandering or searching. Surprise me, Follow a random link, Five a day, On this day and the subject shelves all work offline. Searching inside articles builds its own index the first time, and that too carries on after a restart.

So start the download whenever suits you, pause it whenever you need to, and let Wonder by Zaweba finish the job at its own pace.