The Dreamcast VMU memory cards were innovative devices that allowed you to store game data, play mini-games, and interact with other VMUs. They were produced by Sega for the Dreamcast console, which was released in 1998 in Japan and 1999 in other regions.
The VMU stands for Visual Memory Unit, and it was also called Visual Memory System in Japan and Europe.
The VMU could be plugged into one of the two slots on the Dreamcast controller, and it could act as a second screen for some games. For example, in Sonic Adventure, the VMU could show the status of your Chao pet.
The VMU could also be used as a standalone handheld game console. Some Dreamcast games included mini-games that could be downloaded to the VMU and played without the console. For example, in Shenmue, you could play a QTE game or a Lucky Hit game on the VMU3.
The VMU could connect to other VMUs directly or through the Dreamcast controller. This allowed you to transfer data, exchange messages, or play multiplayer games with other VMU users.

The VMU had a monochrome LCD screen, four buttons, a D-pad, a speaker, and a connector port. It could display graphics and play sounds, making it more than just a memory card.
The VMU ran on two CR2032 lithium batteries, which powered the screen and the speaker. Without batteries, the VMU could still function as a memory card and a second screen, but it could not play mini-games or make sounds.
The VMU had 128 KB of flash memory, but only 100 KB was available for user data. The memory was divided into 200 blocks, and each game could use a different number of blocks.
The VMU came in various colours and models, such as blue, green, red, yellow, clear purple, and gold. There were also some special editions based on franchises like Godzilla, Hello Kitty, and Resident Evil1.
The Dreamcast VMU memory cards were one of the most unique features of the Dreamcast console. They added a new dimension to gaming and made the Dreamcast more interactive and fun.

I purchased 3 VMU’s. Unfortunately only 2 are boxed. I am aiming to get all the different coloured VMU’s boxed.