Wikipedia
DECtape
DECtape (originally called Microtape) was a magnetic tape data storage medium used with many Digital Equipment Corporation computers, including the PDP-6, PDP-8, LINC-8, PDP-9, PDP-10, PDP-11, PDP-12, and the PDP-15. On DEC's 32-bit systems, VAX/VMS support for it was implemented but did not become an official part of the product lineup. DECtapes were 3/4 inch wide, and formatted into blocks of data that could each be read or written individually. Each tape stored 184K 12-bit PDP-8 words or 144K 18-bit words. Block size was 128 12-bit words (for the 12-bit machines), or 256 18-bit words for the other machines (16, 18, 32, or 36 bit systems). From a programming point of view, DECtape behaved like a very slow disk drive.