In Western countries, the era of the console was effectively dead by the mid-1980s, with a flourishing home computer scene replacing it – but the situation was very different in Japan. Nintendo’s Famicom system was starting to flourish and while primarily cartridge-based, ideas from the home computer would crossover into the console world, resulting in the Famicom Disk System – or FDS – which did exactly what it said on the tin, offering disk-based software to run on the console we would eventually come to know as the Nintendo Entertainment System.
The system launched in Japan only, debuting in 1986 – three years after the Famicom itself. The unit could sit beneath the main console, attached to the unit via a serial cable that connected to a ROM cartridge that sits in the Famicom’s cartridge slot. The ROM cartridge contained 32K of memory, 8K of CHR RAM along with an IO chip that also fed extra sound channels to the console via bespoke pins on the cartridge slot among other things. Interestingly, while the FDS could be powered by an AC adaptor, a slot allowed users to power the machine with C-type batteries that would last for months – the power supply bricks were large and power sockets were at a premium in more traditional Japanese homes.
Often considered to be running a variant of standard floppy disks, the FDS was actually based on another system: Mitsumi’s Quick Disk format, with typical Nintendo customisation. The disks supported a total of 128K split into roughly 56K per side, while loading bandwidth worked out at around 12K per second. It’s not exactly a prodigious speed, meaning that some games would have prolonged loading times while others would have an initial load from one side of the disk, before prompting the user to turn over for the data used during gameplay. Other disks actually shipped with different games on each side.
Source: Eurogamer Revisiting the Famicom Disk System: mass storage on console in 1986