I worked from WCRW, Chicago for 5 years ending in the mod-70's. Ed Jacker, the Manager/CE used a DISK recorder that fit in a 19 inch rack. It recorded about 12 hours on each side of a very flexible light plastic disk. The disks were sort of an orange color. We were only on 5 hours daily (shared time) so 4 days fit on 1 disk. Tom Jurek