The actual ferrite core doughnuts do not break down with continued use, BUT moisture or mechanical impact or vibration will damage or degrade the ferrite cores. Otherwise the ferrite doughnut will live and maintain its properties "forever".
The main cause of core memory mat faults is mechanical strain on the X/Y, sense and inhibit wires. This mechanical strain is caused by use and can be made worse by particular usage patterns causing the core memory mat to vibrate producing an audible ring. CDC's Extended Core Storage (ECS) cabinets had a characteristic sound when you opened the doors. Early on CDC 6000 series machines had a lot of reliability problems with core memory, but eventually there was an ECO where the core memory modules were immersed in potting compound to make the core mat rigid to prevent any vibration. This made the once fragile core perform perfectly for the remaining life of the machine. The core memory in my PDP-8/e machines (H212 board) has the ferrite donuts glued to the PCB via some white adhesive presumably to reduce vibrations. Encasing the core mat in potting resin would have been the better solution as it binds the wires to the ferrite doughnuts. Tom On Thu, Feb 2, 2023 at 11:17 PM Jon Elson via cctalk <[email protected]> wrote: > On 2/1/23 22:10, Will Cooke via cctalk wrote: > > > >> On 02/01/2023 3:51 PM CST Paul Koning via cctalk <[email protected]> > wrote: > >> > > ot sure about that. What sort of numbers are we talking about? > >> If all else fails there's core memory, which as far as I remember is > pretty much unlimited for both read and write. > >> > >> paul > > I don't know for sure and can't find any references, but I strongly > suspect that core memory would wear out over time, as well. My reasoning > for this is the because in principle it works the same as FRAM. I usually > refer to FRAM as "core on a chip." Over time, the magnetic domains in FRAM > tend to stay in one polarization or another. I see no reason why the > magnetic domains in core wouldn't do the same. However, a single core is > probably bigger than the entire FRAM chip so there are a LOT more domains. > That means it would take a proportional amount of writes to wear out -- > let's just say a million times. In addition, core access was in > microseconds, whereas FRAM and other modern memories are in nanoseconds. > So it takes something like 1000 times longer on the clock on the wall to > perform the same number of writes. So in the end something like a billion > times longer on the calendar to wear it out. > > > > I would be very interested if anyone actually knows and especially if > there are references available. > > I have extreme doubts that this is true. Memory cores are > just tiny versions of pulse transformers, and similar square > loop transformer core materials are used in switching power > supplies that run for decades at high switching > frequencies. Really, FRAM does not work much similarly to > core. The ferroelectric material is usually lead zirconate > titanate, not an actual ferromagnetic material. It is > written by an electric field, not magnetic, and the electric > field is sensed by a field effect transistor. I have NEVER > heard of core wear-out in magnetic core memories. The > flipping of the magnetic polarization in ferrite materials > does not break down the crystal structure. > > Jon > > Jon > >
