The DH Bit

by D.R.Hunt

Date-line February

Well I guess the topic of high capacity drives on IBM must be drawing to a close, but two further things have come to light. I recently borrowed a high capacity floppy disk (only) controller card made by DTK from Citadel Products of __, _______ ____ ______, Edgware (not to be confused with the Edgware Road), and surprise-surprise, it did the necessary. I could actually force it to format normal 96 tpi. disks to 730K and correctly in an AT clone. To my surprise it didn’t even conflict with the existing hard disk/​floppy controller card, though goodness only knows why ! I can only guess it used a different interrupt or port addresses or something, but the usual lack of information supplied, precluded my finding out.

Mind you, the need to squeeze the last ounce of capacity out of normal disks has eased somewhat, for me at least. New readers may like to have a brief resume of the story. My switch from Gemini with its 780K capacity drives to IBM ATs and clones brought a rude awakening. I could only get 360K of data on normal disks, and the high capacity disks actually cost a lot of money each – anyway I have a lot of normal disks, but object to using them at 360K knowing full well that they would format and work at up to 800K per. It finally came to light that the IBM AT disk controller hardware is so dedicated that using DRIVPARM to modify the format wouldn’t work, so that left two choices. Use twice as many normal disks as I actually needed – or fork out anywhere between £2.80 and £4.50 per disk for high capacity disks.

I now have found another way round that problem but in the process, found another weirder problem than the fun we had deciding why the IBM AT controller wouldn’t format normal disks at 730K in the first place !

The answer came in the form of a mail order company called Mydisk who sell disks at silly prices. The disks are unbranded but carry Mydisk’s own label and a 2 for 1 replacement guarantee if they prove duff. Normal disks work out at about 37p each including VAT and postage (provided you buy by the box of 27 disks) and high capacity disks work out at a shade under a pound each by the box of 13 disks. Now 13 is an unlucky number, but it didn’t stop me buying a box of each to see what made them tick.