ORDINATOR floppy drives

The floppy drives of the ORDINATOR were originally Philips X3122 drives, but they were later replaced with TEAC drives (the X3122 drives were prototypes and had some reliability problems). Both drive types support 5.25" double-sided double-density floppy disks (40 tracks per side), totaling 400K of formatted disk space each.

Although we knew from the beginning that the system would need them, the cost (this was 1983) delayed their arrival until the project was more then a year old. During the summer of 1984 we got four of them, so we also added floppy drives to the Second Exidy computer.

new drive assembly

The original floppy drives featured a hardware door lock, which was not without its problems; during debugging the door often got stuck. The newer drives didn't have the feature; the new drive assembly compensated for this by adding a user-toggable "on-line" switch with LED feedback. This was particularly needed for TS because it could start disk I/O at any time, thus making it unsafe to remove disks without first telling the system so.

Under TS, the floppy change procedure was thus:

turn off switch to tell TS to hold off disk I/O
wait until TS acknowledges by turning off LED
use lever to open drive and change floppy
turn on switch to signal new floppy to TS
LED will go on and TS will read new floppy

The single-user BIOS did not support the switches.