The DECtape formats are compatible with SIMH. SIMH support both the 12 and 18 bit format along with others. PDP-8 .tu56 tapes 380292 bytes long are DECtape 12 bit data words in 16 bit litte endian format (x86). The tape image is normally 1474 blocks of 129 12 bit words. The tapes could be formatted other lengths but are not commonly seen. The PDP-9/10/15 .tu56 tapes around 591872 bytes long are 18 bit data words in 32 bit little endian format. The tape block is 256 18 bit words and the number of blocks varies but is normally around 578 blocks. The PDP-9/15 .tu56 tapes around 442368 bytes long are 12 bit data words in 16 bit little endian format. The tape block is still 256 18 bit words and the number of blocks varies but is normally around 578 blocks. Three 12 bit words can be converted to two 18 bit words with unsigned short inbuf[3]; unsigned int outbuf[2]; outbuf[0] = (inbuf[0] << 6) | ((inbuf[1] >> 6) & 077); outbuf[1] = inbuf[2] | ((inbuf[1] & 077) << 12);