[Info-vax] 8" Floppies

[John E. Malmberg]

On 12/31/2018 2:30 PM, Bill Gunshannon wrote:
> On 12/31/18 3:17 PM, Hans Vlems wrote:
>> V6.1 still has the RXdriverin SYS$LDR. Might still be there in V7.3.
>> All you need is a unibus equiped VAX
>>
> All I got is my 3100's.  :-)  While I had UNIBUS PDP_11's a long
> time ago I have never owned a UNIBUS VAX and only ever worked (at
> the hardware level) on one, also a long time ago!!

I last looked at this stuff a while ago, and I do not have any 8 inch 
media or drives to play with.

What I remember is that 3.5 inch / 5.25 inch floppy controller chips for 
single/double density typically can not handle the data rates needed for 
8 inch floppies.

The high density floppy controllers chips can handle the data rates for 
8 inch floppies.

I remember seeing that a different capacitor value is used for a circuit 
external to the floppy controller chip for 8 inch media than 3.25 inch 
media.  For some reason a data separator circuit comes up in my memory.

There should still be details on the hardware differences somewhere on 
the wild wild web.

Retro computer restorers are starting to use systems like Raspberry Pis 
to build software controllers to connect to or simulate older media.

A TRS-80 color computer can read sectors using ROM DISK Basic from a 
double density 3.5 inch floppy written on an alpha running VMS though as 
a proof of concept.

Regards,
-John
wb8tyw at qsl.net_work