Recovering data from 4mm and 8mm tapes

I've been recovering old data from computers that I used many years ago, the last effort was trying to recover the data from a hard disk that ran a WFW 3.11 system. The problem was the disk could not be read on a modern computer, so I recreated an old system and (very lucky for me) ftp'd the data off the system after I found an ISA network card. I have a couple of 4mm and 8mm tapes that contain data I want to recover. The 4mm is DDS-1 and was written using tar on a SGI system in 1998. My questions are; 'What modern DAT tape drive will read this tape? How backward compatible is this technology?' This seems like an easy problem and intend to use a linux system to read the tape. The 8mm tapes were also written on an SGI system, however it was in 1994 and the IRIX Backup utility was used. IRIX 5 was probably used. Any ideas?