At one time bubble memory was advertised as being able to store huge amounts of data in the size of a sugar cube. I don't remember what the memory density was compared to today's SD cards. What happened to bubble memory - is it still being sold?
Magnetic Bubble Memory (MBM) was a technology that never found a sustained market, and was only briefly in vogue a couple of times in the 1970s and 1980s when market and technical issues hit other storage technologies.
While MBM is non-volatile and fairly rugged, it has a few show-stopping disadvantages, including:
It needs to be heated to over 30 °C before it will operate. Consequently, it is slow to start, has special power requirements and the thermal jacket on top of MBM's complicated structure makes bubble memory quite bulky.
MBM is serial: the ‘bubbles’ race round loops, so memory can only be read or written as the right bubbles come round the loops. In order to speed up access, manufacturers tried many loops in parallel, which added complexity to the MBM module. Even with 512× 8192-bit storage loops, Intel's 7114A from the early 1980s only managed an average access time of 40 ms. This might have been better than hard drives of the time, but MBM was touted as a RAM replacement.
MBM is a complex sandwich made up of a semiconductor substrate layered between precisely-aligned magnetic coils and permanent magnets. Consequently, it would have been challenging to manufacture and likely far less mechanically shock-proof than its lack of moving parts might suggest.
MBM, despite its expected ruggedness, could still develop bad blocks like any other magnetic storage medium. I've heard anecdotal reports of the block remapping process being quite time consuming, and booting machines from MBM could be a slow and not always reliable process.
I remember industry pundits of the time being very keen on pushing MBM as a successful technology, perhaps fuelled by over-optimistic PR from manufacturers such as Intel.
I don't remember what the memory density was compared to today's SD cards.
No, today's flash offers a way (several magnitudes) denser storage, but it is also way less reliable.
What happened to bubble memory - is it still being sold?
It might be still around. Today bubble memory is a rather special niche market with most uses in military and space applications, due to its extreme ruggedness and reliability in harsh environments.
The former bubble memory division of Intel has been spun off as MemTech Technologies and continued development and sales maybe until the early 2000s. The company was active at least until the late 2000s, but seems to be defunct now (See below).
Development continues today. Maybe search for Vertical Bloch Line Technology.
Information found about MemTech:
Scruss did uncover some additional information about MemTech. According to a text to a video about bubble development from 2011 by AT&T they actively offered bubble memory at least until the mid 2000s. Similar with a 2005 article. But here the term Flash is used several times to describe the technology and it's a bit unclear, as at the same time they refer back to prior use in military devices. So maybe they've started kind of transition around that time frame.
He also pointed out a blogpost by John Dvorak fittingly titled "Whatever Happened to Bubble Memory?" from November 2006, basically a 'reprint' of his column from the September 1991 issue of Computer Shopper, mentioning MemTech and Bubbles as present (in 1991).