360K in a 1.2M drive (was: Parallel port hard drives?

Clearly there's a lot of "folklore" muddying the water here. You're right, this is somewhat off topic for the original parallel-port hard drive question. While I was sleeping, someone drove the thread in the direction of solving rather than circumventing the original problem, and that was related to a problem engendered by writing 48TPI media for use on a Commodore machine, or some such, on a 1.2MB 5.25" floppy drive ... I THINK ... I'm a firm believer in transporting data on portable hard drives rather than floppies, since they're MUCH less error prone and MUCH faster and handier. Please see embedded comments below. Dick ----- Original Message ----- From: Pete Turnbull <pete(a)dunnington.u-net.com> To: <classiccmp(a)classiccmp.org> Sent: Sunday, March 26, 2000 6:10 PM Subject: Re: 360K in a 1.2M drive (was: Parallel port hard drives? use, Those are different drives and have the same head gap size problems as the 1.2MB variety. The diskettes for those (720K 5-1/4" floppies) were also a class apart from the run of the mill. Nevertheless, the difference that was essential was the drive, read/write hardware. This included both the 1.2MB drives and the 720K drives in 5.25" size. The media had to be different to support the higher flux reversal density, and the heads had to be more sensitive to flux changes so that they could be driven at levels that wouldn't engender too much crosstalk. Unfortunately, the heads with which 48TPI drives were normally equipped were not capable of this sensitivity, given the original task for which they were designed. Later in the evolution of the technology, media were alleged to be more or less the same, and drives eventually became the same, in the spirit of economy, and one wasn't told whether the drives he was buying were capable of the higher flux-reversal or track density or not. Likewise, one wasn't guaranteed that the media weren't the high-coercivity type, since it didn't hurt the older style of drives to use it. All this has been stirred into the mix of confusion. I would caution against drawing any conclusions from evidence gathered from 48TPI drives after 1.2MB drives became available. The manufacturers were more interested in reducing their diversity than in making drives you couldn't use as "the other" sort. try the amplitude First of all, it's NEVER writing or reading single density. Secondly, the "official" certified media for 96tpi use were always claimed to be of greater coercivity than the ones intended for 48tpi use. I've got boxes of them to prove that. .. cancelled checks, too ... The fact that so many people have "gotten away" (including me, by the way) with writing "ordinary" media at the higher track density only serves to confuse the casual observer. As manufacturers found that they could build all drives with the same heads and electronics at lower cost than building two or three different drives for a given applicaition, they started using the same heads in as large a portion of their drives as they could. It was just good business. The media makers began capitalizing on these same economic decisions, and started filling their orders with "better" emulsions, and selling the excess into their lower-grade market. The higher coercivity media were required because the signal sensed from the heads is a function of the head gap area versus the media area and the density of the magnetic field within that area, given that the velocity of the media at the head is a constant. Speeding up the heads increases the signal amplitude at the amplifier input. Now, if there is signal written at the same track width as the maximum the head allows, the signal will be as clean as it can be and maximal. If the signal track is WIDER than the head gap, it is still maximal and still clean, as any crossover effects will be synchronized with the signal, since the head is surrounded, ideally, on both sides, by signal similar to what it is supposed to read. When the head is wider than the signal track, the unerased signal from the wider head which previously wrote the track is still present at the margins of the track as seen by the narrower head gap. However, the head gap is fully loaded with signal bearing media surface and "sees" only what it is supposed to see. The wider head, however, when it "sees" the signal from the narrow head gap also sees the signal from a wide head gap that differs interferes with the operation of the read/write system.