Scor­pio News

This would provide for a complete session with one set of four disks, little scope for operator error, and a full backup at the end of the session.

The alternative option of buying a surplus hard disk was not attractive because I have no previous experience of these, and no hard disk controller. The ease of copying using identical floppy drives was also very seductive, as the copy is physically identical to the original. The sensible option of buying a plastic box from Amstrad at a very reasonable price was also rejected, on largely sentimental grounds!

Having taken the plunge and ordered the drives, I had a number of problems to solve, some of which I anticipated, and others which appeared later. Any project involving a mix of hardware and software poses diagnostic problems when it doesn’t work, and this was no exception.

I had anticipated the following problems:–

1. Interfacing to the VFC board.
2. Clock changes on the VFC board for the higher data rate.
3. Power supply requirements.
4. BIOS changes, to deal.with two-byte track numbers.

I should also have expected:–

5. Incorrect and incomplete hardware documentation.
6. Faulty drives.

The Drives

The Drivetec 320 floppy disk drive is a double sided half height 5-1/4 inch unit. It uses 160 tracks per side, with an unformatted capacity of 3.3 Megabytes. The disks supplied were formatted with seventeen 512 byte sectors per track, giving a total formatted capacity of 2720 k.

In order to cram so much data on to a track, it is essential to use the higher data rates used for 8 inch drives (i.e. 500 kHz instead of 250 kHz), and to double the track density to 192 tracks per inch. This requires exceptionally accurate tracking, and a dual stepper closed loop servo system is used to achieve a claimed accuracy of 200 micro inches. Like eight inch drives there is a head load solenoid which lifts the head off the disk after a time-out delay set by the FDC, and this solenoid also actuates a door lock. Although the manual states that the motor runs continuously, this is not so.