winkler@harvard.ARPA (Dan Winkler) (08/20/85)
Here's an explanation of the problem I was having with get20. I was using it to transfer binary files from Simtel20 to this Unix Vax. When I did, I would get strange files that had some recognizable text in them. If I ftp'd the same file in tenex mode, it arrived properly. Here's why: > From towson@AMSAA.ARPA Tue Aug 20 10:54:56 1985 > > Dan - SIMTEL20 is a DEC-20, which has a 36-bit word-length. UNIX machines > that I know of have either 16 or 32-bit words. Thus, there is no way that a > straight binary (i.e., image) ftp transfer can map correctly from the DEC-20 > to a UNIX machine. Binary data are stored as four 8-bit bytes per 36-bit > SIMTEL20 word, with the low-order four bits of each word filled with zeros. > If such a file is interpreted as a contiguous string, as will happen if a > straight binary transfer is made to a 16 or 32-bit UNIX machine, the four zero > filler-bits per 36-bit group will cause rather bizarre and frustrating > results. You will get alternate groups of four good bytes, four bad, four > good, and so on. String searches will turn up some recognizable text, but > just enough to drive you nuts. Tenex mode causes the DEC-20 to unpack the > data into 8-bit chunks (with no filler bits) before sending it to the UNIX > machine. > > Good luck, > Dave So if you want to use get20 on a Unix machine, you better make sure that it's using tenex mode. Dan.