64DD is a magnetic disk drive peripheral for Nintento 64 that released only in Japan. "64" stands for Nintendo 64 and the 64 MB storage capacity and "dd" stands for disk drive or dynamic drive.
Useful info:
It was announced in 1995, prior to the Nintendo 64's 1996 launch
Release date: 1 December 1999 in Japan
Discontinue date: 28 February 2001 in Japan
Sold more than 15,000 units
Main hardware enhancements: more storage, a real-time clock (RTC) was added, Internet connectivity
