New stock of 1130 disk heads (probably) and working to try to simulate DRAM on RK05 board

EARLY IBM DISK DRIVES WROTE AT 720 KHZ, USED CHROMED METAL HEADS

Drives such as the 2310, 2311 and 2314, introduced along with the S/360 generation of computers, used metal disk heads that wrote tracks of .05" width, spaced .1" apart at a bit rate of up to 1.25 Mb/second. The head flew 125 to 160 microinches above the platter surface on a cushion of air. 

Head-Disk Interference (HDI), colloquially called a crash, was caused when the head contacted the spinning platter or some bit of debris that jammed between the two. These can range from very brief and relatively low energy skips up to events where the head digs into the magnetic coating on the platter, forming a gouge. In the worst case, the head can even snap off its welded connection to the disk arm. 

The chrome surface of the heads will accumulate slight scratch marks from the small HDI events but continue to provide good reliable service, but as the scratches grow and deepen, they can amass oxide material and eventually lead to a more major HDI. 

IBM licensed the disk technology to a number of companies, including many minicomputer makers who developed their own single and multiplatter disk drives along the same lines as the IBM drives. However, one enhancement that was introduced by the industry relatively rapidly was to construct heads out of ceramic rather than metal. The ceramic was much more resistant to scratches and therefore reduced the more major HDI events as well. 

The ceramic heads also featured a higher bit rate, allowing twice as many bits per linear inch. This meant that the same single 14" platter (2315) that held about 1MB of data with the metal heads would hold 2MB with new ceramic heads and corresponding electronics improvements. The heads continued to evolve, dropping the width to .025" allowing twice as many cylinders on a pack. The two improvements offered 4X the capacity. 

Licensees such as Diablo produced 2310 style single platter drives with options to use either the metal or ceramic heads. The only market for drives with the metal heads was to provide compatibility of cartridges between IBM 1130/1800 and these minicomputers. The majority of the sales by non-IBM vendors featured the extra capacity from use of ceramic heads. 

As a result of all this, the supply of used disk heads from that era are overwhelmingly the ceramic style. There might be a sale once every five years of a metal style head. This is a serious impediment for 1130 systems, as the spare parts have become unobtainium. 

Fortunately, I received a generous gift of a set of heads for an IBM 2302. This was a fixed platter device - 25 platters that were permanently part of the machine - instead of the 1, 6 or 11 platters of the removable cartridge machines. This nonremovable stack of platters allowed for a wider recording area, featuring 500 cylinders versus the 200 cylinders of the removable type drives. 

In order to moderate the cost of moving the heads across 5 inches in a maximum distance seek, IBM provided a set of heads that reached the inner 250 cylinders and a second disk arm that covered the outer 250 cylinders. These could move independently.  I received a partial set of arms from an IBM 2302 and looked closely at the metal heads. 

Diablo head at top and pair of heads from 2302 below it

They appear identical to the heads on the 2310, 2311 and 2314! Thus I have heads that can be used to repair 1130 disk drives. The head is mounted on a larger sturdy structure; these larger structures vary by disk drive type, but the head itself appears exactly the same. I will do more work to verify this but I am excited to have this potential supply of spare parts. 

WORKING ON MORE COMPLETE SIMULATION OF MY VIRTUAL 2315 FACILITY

I have done some simulation of the logic I created, as an adaption of the RK-05 Emulator, to emulate the IBM 2310 (thus the internal drive of an 1130 computer). However, it wasn't as thorough as I achieved when working on the Diablo Archiver project. Having gotten DDR3 DRAM simulation to work on that other project, I began looking for simulation files to model the Winbond W9825G6KH SDRAM chip that is used on the RK-05 Emulator main board. 

The vendor did provide such files, encrypted verilog, using keys for the three main simulator families including the Vivado simulator. However, I could not use them. The reason is that AMD/Xilinx only keep the keys they issued for five years. This encrypted simulation model was shipped more than five years before the 2024.1 release I am using. The simulator can't decode the file and without the key nobody can recreate the code for the simulation of this chip. 

At this point, I might be able to find and download an earlier release of Vivado or its predecessor software, one that still has the key to decode the simulation file. This would be installed on a different PC just for the purposes of simulation. As it is, the actual FPGA bitstream for the RK-05 Emulator is not produced on any version of Vivado since it doesn't use a Xilinx FPGA chip. I simulate and test on Vivado and only then generate the bitstream on Lattice Icecube2 software to load the hardware.