Re: [Altair Computer Club] Re: Selling ALTAIRs and IMSAIs
>BTW, please tell me more about supporting 3.5" drives on your (ex)I have 3.5 and 5.25 disks connected to a tarbell. The Tarbell thinks
>IMSAI. If it isn't Altair related, you can contact me offline, but I
>expect everyone would be interested in what you did.
the 3.5" disk is a 5.25" disk, which means the 3.5" disks are
unreadable on any other computer and that they have a formatted
capacity of 70K.
My tarbell isn't reliable though...
- On Sunday, February 24, 2008 at 5:49 PM, Grant Stockly sent:
>I'm using a Cromemco 64FDC in double-density mode and am
>>BTW, please tell me more about supporting 3.5" drives on your (ex)
>>IMSAI. If it isn't Altair related, you can contact me offline, but I
>>expect everyone would be interested in what you did.
>I have 3.5 and 5.25 disks connected to a tarbell. The Tarbell thinks
>the 3.5" disk is a 5.25" disk, which means the 3.5" disks are
>unreadable on any other computer and that they have a formatted
>capacity of 70K.
driving all of my diskettes in double density. If memory serves,
the 64FDC has a "full size/mini disk" conditioning bit that
supports both 8-inch drives and 5.25/3.5 inch drives. The
3.5 inch drives bolt up to the same cable as the 5.25,
although you have to pay attention to the drive address strapping.
In any case, I have two 8-inch, one 5.25 and one 3.5 inch drives
hooked to the system and typically boot off the 3.5. I hacked
the BDOS and my boot ROM to prompt me for the boot drive so
I can boot off any of the above drives (A,B,C, or D), which is
nice when one goes flakey.
I'm also running double sided on my 5.25 and 3.5 diskettes along
with a sector size of 1024 bytes. Doing all this, I'm getting about
1.4MB per diskette, if I remember right (I'm not near the comp
I really like the Cromemco 64 FDC because it has a serial port for
the console and a boot eprom (2716 or 2732) which powers up enabled,
but which you can disable using Cromemco's write to port 40H method,
which disables boot eprom and enables RAM. My boot ROM simply
moves itself into low mem then jumps to that low mem. First
instruction then disables the rom/enables the upper RAM, thereby
alllowing me to run a full 64K system. I tied the Cromemco
recognition of their port 40H bit to the Phantom line on the
bus which lets me use the Cromemco method with some non-Cromemco