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Ferrites, that's it!? The ones on this cable actually appear very plastic and light weight, and are not snap-on. In any case, I have to apologize for the unintentional misinformation.? The Centronics end is actually 36-pin, and I had a vivid "picture memory" of its purpose this morning.? It connected the printer to My First Computer, a Laser 128 (Apple IIe/IIc clone).? Funny how memory works.. I can totally picture the cable running through the old computer desk, etc.. So does anyone want to explain the difference between DB and DA? >________________________________ >From: "Ricker, William" <William.Ricker at FMR.COM> >To: Dan Kressin <dkressin at yahoo.com>; BLU Discuss <discuss at blu.org> >Sent: Wednesday, November 2, 2011 11:23 AM >Subject: RE: [Discuss] OT: what is this cable for? > >>? Ribbon cable w/ two (the name escapes me ..) "ring things" to usually used to fight inductance..? > >Snap-on Ferrite donuts actually *add* inductance, which rounds the corners of square wave digital signals, to prevent interference (both by and to) and/or induced spikes from lightning EMP. They come in a variety of specs which attenuate into progressively lower frequencies. Use the wrong one and you'll attenuate the desired signal too ! > >(One more pedantic than I might object that fighting interference is fighting *mutual* inductance, but that's not a measurable inductance outside of cross-talk range.) > >Yes the DA-15 was used as Game/MIDI port on early IBM PC ISA sound cards. But the normal MIDI adapter cable would have been DA-15 to pair DIN-5 (or XLR3). Since the game port was re-used to drive all sorts of things, that's a possible origin, as are any custom frobistats. The C-50 / CN-50 was abused as an easy expansion interface for lots of pre-miniaturization devices -- it was originally a family or range of telco analog connectors for twisted pair snakes, eg multi-line phones & PBX to punchblock cabling, that was adopted for printers, re-adopted for SCSI-1, because it was available relatively cheap due to volume of telco use. As the RJ series has been adopted more recently. The C-36 had obscure computer uses, not sure if larger sizes were ever digitally 'appropriated'. > >Bill @ $DayJob > >
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