Jerome Fine replies: I notice that there have been a number of replies to this question and, if I might summarize what I have read, it seems as if the answer depends on if the responder could (or could not) use the (I believe you have received) the DLT III tapes (since as far as I know DLT I and DLT II tapes were actually the CompacTape I, for the TK50, and CompacTape II, for the TK70). FIRST: In the 1990's I used BOTH CompacTape (by default it was CompacTape I) and CompacTape II media without any problems in both TK50 and TK70 drives - although when I wanted to switch between which drive would WRITE the tape, I always did a BULK ERASE. If the tape was completely unused (very rare for me an I only ever had about a dozen), both TK50 and TK70 drives could be used. SECOND: I always verified the contents of any backup files written to the tape and over a period of about 10 years, I can't remember having had more than isolated problems with the verify operation which consisted of a completely separate comparison AFTER all the backup files had been written by the TK70 and the tape switched to WRITE PROTECT. THIRD: A memorex site (long since disappeared) provided all the physical and magnetic properties of the DLT line of tape media starting with CompacTape I, CompacTape II, DLT III, DLT IV, etc. The physical and magnetic properties of BOTH CompacTape I and CompacTape II were IDENTICAL (which reflected my experience in using them on either TK50 or TK70 - but with BULK ERASE in between). The DLT III tapes had a much higher magnetic rating and I seem to remember reading that they can't be used with either the TK50 or TK70 drives - even if you can overcome the small physical differences. And, of course, the CompacTape media can't be used where DLT III media are required. The following point is based on my use of the TK70 drive and media when they were used to hold 32 MB backup files which were written under RT-11 by BUP using a PDP-11/73. I only used the TK70 for this one purpose (well about 99.9% of the time). THe disk drives were 600 MB ESDI Hitachi and the disk controller was the RQD11-EC. FOURTH: While many individuals over the years have attempted to justify the higher price of CompacTape II media over CompacTape I media by saying that the quality control was better, etc., my experience over those 10 years when I used TK70 drives and CompacTape I media after a bulk erase (90% were used media from a TK50) was more than satisfactory. The TK50 could write a maximum of about 50 MB on a tape while a TK70 could write over 256 MB on a tape. IN ADDITION, the TK70 wrote the same file about in about 1/3 of the time on a PDP-11/73, BUT FOR ALL PRACTICAL PURPOSES, it was impossible to verify the file using a TK50 except to restore the backup file to an unused RT-11 disk partition and then compare the "restored" RT-11 disk partition against the original RT-11 partition. This was because the TK50 could not be kept in streaming mode while the comparison was being made even though with the identical hardware and software (except for the TK70 drive and controller of course) the TK70 was able to perform the VERIFY operation in about the same time period (about 7 minutes on a TK70 vs about 19 minutes on a TK50 - if I remember correctly) as it originally took to write the backup file under RT-11 using BUP. By the way, I have a large number of CompacTape I media which I no longer will be using, but they will need to be bulk erased since they have all been initialized in a TK70. Assuming they are still usable, I will look into selling them. I am in Toronto (M2R 3G3). Sincerely yours, Jerome Fine -- If you attempted to send a reply and the original e-mail address has been discontinued due a high volume of junk e-mail, then the semi-permanent e-mail address can be obtained by replacing the four characters preceding the 'at' with the four digits of the current year.