FridayAFM - Mini Hard drive

Héctor here, your AFM expert at Nanosurf calling out for people to share their Friday afternoon experiments. Today I image one of the tiniest hard drives I ever saw.

The story goes something like this. A few months ago I was watching Linus Tech Tips when I came across this video about a microdrive the size of a coin, and I immediately knew I had to image it.

Not only because of its tiny size, but also because it will be a nice addition to my magnetic storage media series (according to the manufacturing date, the drive I got is from 2006-02-28).

The drive itself was not difficult to find, I got one of ebay for about £7, but it was challenging to disassemble as it requires "Y" type screwdrivers (which I don't have), so I had to resort to the old trick of using a sharp blade.

Once opened, it resembled many of the other disks I have seen, just that every component has been miniaturized. Spinning disk, motor, reading arm...

1 Seagate ST 1.2 hard disk drive.

So, the important is question: How does it compare with other hard drives I have imaged in the past? This is when it becomes handy that I included bit density calculations in previous fridayAFM posts... and in other measurements I did but didn't post (because it would be boring seeing MFM images of hard drives all day long).

All we can say at the moment is that the electronics are smaller, maybe because it includes custom-built ICs? (covered in black epoxy), although these could be just the amplification ICs that usually are mounted on the reading arm (here, because of the tiny size, even though they are placed outside, they are still close to the reading/writing sensor).

But is the bit density any different than hard drives from the same era?

Here is the MFM imaging of the disk:

1 Topography and MFM images of Seagate ST 1.2. Using standard 2-pass MFM and PPP-LM-MFMR probes. First pass free vibration amplitude ~ 50 nm peak to peak, and setpoint at 50%, second pass free vibration amplitude ~ 25 nm peak to peak, with a lift height of 25 nm.

The only thing notable about the MFM imaging on this mini disk is that I couldn't disassemble the platter, so I have to image directly on the disk still attached to the drive. 

So, how does it compare? Before showing you the comparison with other hard drives, let me show you two interesting hard drives (If I don't show them here, I might not have other chance). I present you the Fujitsu MPC3084AT from 1999.

1 Fujitsu MPC3084AT hard drive. MFM images taken using standard 2-pass MFM and PPP-LM-MFMR probes. First pass free vibration amplitude ~ 50 nm peak to peak, and setpoint at 50%, second pass free vibration amplitude ~ 25 nm peak to peak, with a lift height of 25 nm.

The weird thing about this drive (the Fujitsu), is the magnetic domain pattern. There is a lot of spacing between tracks. Obviously the writing/reading process can deal with bits closer together, so why are the tracks so large and separated? My hypothesis is that the mechanical movement of the arm (or its electronic controlling circuit) is either not stable enough, and large spacing is needed, or it doesn't have the resolution to have smaller spacing between tracks. This fits well with the fact that the arm is a large structure with 6 read/writing heads, because such large structure is likely to vibrate.

By the way, this was produced about ten years before Fujitsu's hard disc drive division merged with Toshiba. It will be very interesting to see Toshiba's drives before/after and Fujitsu's closer to the merger/acquisition.

The next hard drive goes back another ten years, to an era when it was still consider (for economic reasons) possible to have hard drives as cartridges (eventually this was discarded to be able to reduce tolerances and get rid of dust contamination among other reasons).

1 Mass microsystems Datacart 88. MFM images taken using standard 2-pass MFM and PPP-LM-MFMR probes. First pass free vibration amplitude ~ 100 nm peak to peak, and setpoint at 50%, second pass free vibration amplitude ~ 50 nm peak to peak, with a lift height of 300 nm.

The curious thing about this drive is the strong stray field. Using standard 2-pass MFM and a lift height of 300 nm during the second pass, the phase change was still of few degrees (compare with the 0.1 deg of first image... as all these were taken with the same probe). More on the history of Syquest on this youtube video.

Now, without further a do, here is the summary of hard disc drive bit density over the years (at least as it stands right now after my first year with Nanosurf, because I have many more drives waiting to be characterized).

1 Hard disc drives. Evolution of bit density over the years.

So... the answer is that the Seagate ST 1.2 is no special, its bit density fits perfectly with the drives been produced in 2005-2006. It simply has scaled down mechanics, the spindle shaft takes less of the usable disc surface... and probably the electronics are tailored for these drives, maybe compromising on bit correction algorithms, or de-noising, or algorithms to maintain hard disc drive health (e.g. periodically reading and writing bits to avoid data degradation).

Interestingly, from the graph we can also see the deep about 2008 when the economic crisis. Probably indicating that for a few years spending on development was reduced. We will see a similar deep with the Corona pandemic?

Also worth nothing that the Bernoulli box (1983), seems to have a bit density higher than storage formats coming out at the same time (that or I got the date wrong, or the bit density calculation).

Almost forgot, worth comparing this graph against the one in the Computer History Museum.

Now, for those who missed it, here are the previous posts on magnetic data storage media.

1 FridayAFM of  2022 09 02. Height (left) and MFM (right) of floppy disc, diskette, and Zip disc.

2 FridayAFM of  2023 01 02. Toshiba MK32 from 2011

3 FridayAFM of  2023 02 24. Bernoulli box from 1983.

4 FridayAFM of  2023 03 31. CF2 diskette.

5 FridayAFM of  2023 04 28. Miniscribe from 1989.

Hopefully, these, and some more questions that I will keep to myself, will be answered in future fridayAFM experiments (or maybe you know and are willing to share the knowledge?). 

Stay in touch, and share images if you have other hard drives, I can add them to the graph!