DECtape
Tape Data Recovery - DECtape
DECtape was a type of magnetic tape data storage medium used in many versions of Digital Equipment Corporation computers, including several PDP models and LINC-8. DECtapes were designed to be reliable and durable and was used as the main storage medium for an operating system. The DECtape drive was able to run a small operating system such as OS/8 or OS/12. The OS would put the temporary files on a second DECtape, so that it can increase the speed of access to the main drive.
DECtape was ¾ -inch wide and is formatted to contain blocks of data that can be read or written individually. Block size was 129 12-bit words for the 12-bit machines, or 256 18-bit words for the other machines. A single tape stored 184K 12-bit PDP-8 words or 144K 18-bit words. DECtape used dual-redundancy method and so could keep the error rate low. Each bit was written twice across the width of the tape, using a method called Manchester encoding (PE).
DECtape II
DECtape II was introduced around 1978. It had the block structure similar to the original version, but it was on a special pre-formatted DC150 miniature cartridge tape with a transparent plastic cover mounted on a ridged metal base. The TU58 DECtape II drive was featured with an RS232 serial interface, which allowed it to be used with the ordinary serial ports typical of DEC’s contemporary processors. TU58 drives were used in several different systems including the VAX-11/730 and /750. A DECtape II cartridge had a capacity of about 256 kilobytes.
