Bubble Memory
en.wikipedia.org55 points by jacquesm 3 days ago
55 points by jacquesm 3 days ago
In Patriot Games by Tom Clancy, there is a scene early in the book where Jack Ryan is talking about the laptop he is using to write his book.
I don't remember the exact specs but am 100% sure he mentions that it has bubble memory.
I find pretty interesting that the memory is not perfect out of the fab and its defects are coded on its label, hence these defects can be loaded to the device using it as a map, so it can work around these loops while working.
Now, this is even true for flash memory, but this is handled at the controller level and its dynamic during its initial "formatting" at the factory, so it's completely hidden from the host unless "host" is the controller.
OTOH, bubble memory comes with a "this machine has no brain, use your own" sticker on it.
Hard disks used to come with a paper label listing their bad sectors. (They still come with a list, it's just now it is hidden in the firmware like you describe.)
I do some retro-computing every now and then and of these old drives that still work (about a 50% chance), when I format them assuming all sectors are good, they will inevitably report the same bad sectors as is on the label.
I don't really know why "bad sectors are still bad after 40 years" is so surprising to me, but there you go.
There's a step which "flashes" the magnetic structure on the disks during manufacturing which also allows drives to navigate the disk surface and "see" individual sectors. The bad sectors list from factory shows the points where this process has failed due to bad coating or other anomalies.
So they are not worn out sectors, they were bad (or not there) from the start. You can't rub them out, because there is not enough magnetic flux or material to store data at that address.
And the firmware remaps them, as far as I know. That's very different from a firmware exposing a bad sector list to the host, which is the case for some flash systems, I believe.
Disk firmware follows sectors which are hard to write, flags them as "current pending sector". Then reallocates that sectors data to one of the reserves when it has time and increases "Reallocated Sector Count", and if it deems the sector dead or unusable, it's get blacklisted and "Offline Uncorrectable" count is increased as well, from what I remember.
This is all transparent from the host, maybe an occasional "wait a little, I'm kinda busy" signal to the controller. Same for flash, but it's way faster and more transparent, since the real map inside the flash controller is never linear, anyway.
Not nearly all flash systems (including NAND based ones) use a dedicated controller. I believe e.g. iOS devices have for a long time still handled bad block handling in software, while macOS has always handled it in hardware.
Systems running macOS (i.e. Mac systems) use SATA or NVMe disks (depending on their age) which come with their own controllers, hence it's always isolated from the OS except SMART data. I have no idea about iOS systems.
Controller based management is also true for SD cards of any form, CF cards, USB flash drives or any external drives. This makes only embedded systems and devices like phones with direct NAND/NOR management AFAICS.
I remember a lot of talk about how transformative bubble memory was going to be circa 1980 and then quit hearing about it.
I really enjoyed this 2025 video from The Retro Collective explaining this technology (with some rather fun arts-and-crafts examples) and showing off a Konami arcade board (sadly nonfunctional, but still cool to look at) that used it.
I had initially learned about bubble memory from the Logopolis serial of Doctor Who. I actually went and looked it up after watching it because the concept sounded neat
We used Intel 7110 magnetic-bubble memory in our mobile robot. CMU early 80s. VMEbus I think it was.
Thanks for the in-depth explanation of this system. One of the most mainstream and famous use of bubble Memory may be the Gradius (Konami) shoot them up PCB and its infamous loading/warmup screen.
See also: https://en.wikipedia.org/wiki/Ferroelectric_RAM, which has been used in a few quite popular systems as well (e.g. the PS2 memory card supposedly uses it for some high-rewrite-count operations).
MRAM (magnetic and non-volatile) had some applications in GBA cartridges to replace small amounts of battery-backed SRAM.
FRAM is also used in all modern MSP430 microntrollers from Texas Instruments. Amazing technology
That reminds me of core memory, which is also nonvolatile and for a long time was the primary memory of many computer systems.
I suspect "growing up" with a system where the computer itself is nonvolatile (turn it off, move it, turn it on, it's doing exactly what it was doing when it was turned off) changed the way people looked at computers vs modern systems.
It's too bad intel didn't push harder on their optane stuff. I guess it's too bad (for intel) for lots of different abandoned / failed projects.