positron@cosmic.berkeley.edu (Shigeki Misawa) (04/03/91)
Hi. I was wondering if anyone can steer me to some information concerning 8mm tape drives and connecting them to unix systems. In particular, I am interested in how data is written on the device and how it is read back by the controller/computer. (I am not interested in such details as the analog signals or the helical scan stuff, I am really interested in such things as physical tape marks, end of tape marks, end of file marks, end of record marks which may or may not be used in 8mm tapes and whether things like this are under operating system control or under control of the tape controller) I am interested in this information because I will be writing tapes from a VAX and/or a custom VMEbus multiprocessor and reading them back on a UNIX box. I would have thought that the tape drive would act as a system that would accept a byte stream from the computer. This byte stream would fill up some buffer that would be flushed out to tape, at which point some sort of end of buffer mark would be written by the tape controller to tape. Because of this, I would expect that the computer/OS would insert record/file information (including end of record, end of file, marks etc) into your file and send that to the tape drive to be stored. When the tape is read back, I would expect that the OS would filter this extra information out of the stream and hand the information to the user program that is reading the information. This gets to the question of reading non Unix tapes on a Unix system. I expect that the other OS's would insert incompatible information on the tape. Is there a way to read bytes off such a tape with relatively standard C calls? If anyone can steer me to any information that will give me any information that may clear up any misconceptions on any of the above topics, I would be greatful. Thanks in advance. Shigeki Misawa UCB Physics Department Grad Student