80-Bus News

Disk reliability

Now all those with disk systems will be aware that those square 5″ (and 8″) black plastic things known as disks are relatively expensive, and that even though disks are fast, prolific code or text writers, or itinerant software lifters will be fully aware that their capacity is limited and that new disks will be required sooner or later. Those blessed with high capacity disk drives, 400K – 800K per drive, et al, will be in the fortunate position of having to purchase fewer disks than those who only have, say, 70K per drive. However, if you believe the propaganda, those with high capacity drives will have to pay more for their disks anyway. Well, I propose to have a brief look at disks, and from my own experience, dispel a few old wives tales, and probably create a few heresies in the eyes of the manufacturers.

Firstly, let’s have a look at the different breeds of disks, they are available from about £15.00 per ten to about £50.00 per ten, so what has one manufacturer got over another for the price? Well firstly, there are a lot fewer disk manufacturers than there are brands of disk. A lot of badge engineering goes on, not only sticking a particular computer manufacturers’ name on the disk and shoving the price up accordingly, but also producing the same disk with different labels to sell in different markets at different prices.

Disk Oxides

Now on to the oxides used on the disks: once upon a time I used to read everything I could on the various types of chemistry that went into the manufacture of magnetic oxides for recording purposes, and the ground rules laid down for audio recording are in many ways the same for digital data recording.

Without being in the least technical, and committing my first heresy by making the the broadest of generalisations, there are two types of oxide, the dull brown stuff and the shiny black stuff. In general the brown stuff is softer (physically) than the black stuff and slightly more prone to wear than the black stuff. However, the brown stuff requires considerably less recording head current to reach magnetic saturation, and so is more suited to drives which have low head currents. The reverse is true of the black stuff, it is (physically) harder and requires considerably more head current to saturate the media.

Ignoring the wearing capabilities of the disks, which in normal home use are minimal anyway, it seems the choice of magnetic material is down to the head recording currents of the drives, in other words, those drives with lower head currents would prefer disks coated in the brown pudding, whilst those with higher head currents would prefer those with the black pudding but will work equally as well on the brown pudding. So how do you know which type of drive you have? Unfortunately this is the sort of information that manufacturers of drives don’t tell you as the information is contained in the OEM (Original Equipment Manufacturers) technical manual, and you usually aren’t privy to these. Apart from that, how would you know whether the head current given in the manual to create a saturation of X mWebers is high, low or indifferent without samples of all the drives around? Fortunately, the solution is easier than this, if somewhat empirical. If the drive was designed (designed, not necessarily manufactured) more than about 5 years ago, it is almost certainly more suited to the brown pudding. More recent designs keep step with improving media technology (lovely buzz phrase that, media technology) and would be suitable for both the brown and black puddings.