IBM channel-attached DASD emulation

Henk Stegeman h.j.stegeman at
Sun Dec 27 03:29:18 CST 2015

Hi Mike,

Here are the options to attach 3340 DASD emulation to an IBM System/3

1) direct connect to the internal channel of the S/3. Some disk OEM's did
Requires a FPGA with at one side MST-1 interface logic and at the other side
IDE or SCSI interface.
The availabe IBM documentation is complete enough to finish this project.
You need good IBM HW & VHDL knowledge.

2) direct connect to the BUS/TAG interface connector.
This needs a 8+P bit stream. You have to do some reverse engineering to
figure out what the exact format is.
I have no idea if the HW must be implemented in a FPGA (for timing reasons)
or if an AVR processor will do the job.
Advantage is that you don't have to modify anything inside the S/3.

3) IBM has implemented an IOP (I/O Processor) between the S/3 CPU and the
3340 drives.
This IOP is a modified version of the ones used in the IBM 370/115 & 125. It
is a powerfull multi thread capable beast.
With small HW modification you can connect an IDE or SCSI drives to it.
The difficult part is modifying the firmware of the IOP. This requires a
special assembler (to be written) and very good assembler skill's.

All options requires quite alot of time to implement.

My 2 cents


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