Memory Cards for video game consoles originated from the Neo-Geo AES console made by SNK. It had since then inspired rival companies to come up with their own game storage devices. Popular and mandated use survived for nearly a decade and over thanks to the PS2's lifespan and the Wii's backwards compatibility as such consoles now had internal memory support
As mentioned, the Memory Card was used to story saved game data from multiple titles. Fifth and sixth generation consoles contained two slots for where the cards were to be inserted. Excluding the N64, players could check the neutral menu on the console to view their files. However, they have finite storage and can only contain data space at once. They may choose to delete unwanted data or copy it to a different card. Data was divided into 'Memory Blocks' (MB) as certain games, particularly vast ones, took up a lot of memory for vacant save files. With the sixth-generation consoles, Memory Cards became an absolute necessity as all of them used discs in lieu of cartridges which had their own save battery. Memory Cards with enhanced storage could be purchased at electronic media stores.
Despite that the N64 used cartridges, and thus, had save batteries within the games themselves, some games still required the use of a memory storage device which came in the form of a Memory Pak, which was inserted into the slot on the back of the controller, rather than inside the console. The Pak's storage was divided into 'pages' and a small blank space on the back of the card was placed onto it, allowing players to write down important contents.
The Dreamcast had a particularly innovative variation called the VMU (Visual Memory Unit). Like the N64, the VMU was inserted into one of the slots on the back of the controller, rather than on the console. Unlike other Memory Cards, the VMU had a LCD screen on the front along with buttons. The screen would display something according to the game currently being played, showing either small chibi animations corresponding to modes and/or situations or simply the title of the game. Some titles provided mini-games available for play for the VMU through saved data.