Handheld gaming consoles weren't always the mobile powerhouses they are today. Indeed, before the days of the Nintendo Switch or even the original Nintendo Game Boy, they were essentially just LCD screens that lit up different parts of a single image to simulate on-screen movement.
In other words, every sprite belonging to any given game needed to be packed onto a single screen, as seen below:
Furthermore, unlike the Game Boy and other newer portable devices, early handheld games were sold as individual units. For the most part, you couldn't simply buy one main device and slide a different game cartridge in.
If you've been gaming long enough to remember those days, the Internet Archive has some good news for you. As part of their ongoing efforts to build an "Internet library," the website has launched a "Handheld History Collection" that contains a whopping 60 emulated versions of classic handheld titles.
For now, those titles include the likes of Mortal Kombat, Q*bert and Contra but if you don't see one of your favorite games in the current line-up, check back frequently - archivists will reportedly be adding many more in the near future.
Naturally, all of these titles are available for free and come complete with original game assets and sounds. However, it does not seem possible to download the games to your own system, so if you want to play them you must do so on the Internet Archive website.
If you're wondering how the Internet Archive team accomplished this feat, you can read some of the technical details on their official blog.