RLL encoding is the normal path in technological progress, directly based on the old MFM standards.
This 5.25" half-height disc drive can be recognized in a system without opening it's case. It makes a powerful weird noise when the spindle motor spins up and down. Once you hear that noise, you will not forget it. It's quite unique. This is a RLL disc drive that I bought in 2003 from a bazaar at a price of about 1$. I also bought a Western Digital WD1004-27X for 1,5$ and when I got home I mounted the whole disc drive system on an Unisys 286/10MHz based computer. After running the MS-DOS DEBUG.EXE program which I used it to launch the embedded BIOS at address C:500, I used FDISK to partition the drive and then issued a FORMAT C: /U command.
Then I had a clean RLL disc drive with only 13 bad sectors. Luckily enough, those bad sectors were in range first 1Mb-first 5Mb of the disc so I filled that portion with a dump file. After that, I installed MS-DOS 5.0 and Windows 3.1, a perfect pair. I found the disc drive a little bit slower than I'd wanted so I tried installing it in an AMD K6-II/500MHz computer equipped with a Soyo motherboard. I thought that the 8-bit ISA bus on the 286 was working at something less than 8MHz but I guess I was wrong. The drive refused to work until I disabled the internal IDE host adapters (channel 1 and channel 2) and set the memory range of the controller: 324-327h: CA00-CBFFh. The disc was running a little bit faster (placebo?) but what can you do when the actuator has a high latency. They claimed the internal transfer rate is 7,5Mb/s.
This is one of my favorite disc drives so that's why I spent so many lines of writing to describe it -- I guess that the picture says more about the visual aspect of the drive than I could say in words. I do like the way Seagate has built this drive. It has a nice shape, standard for the period, but looks a little bit outdated. Also the green LED lights way too much.
I think this drive is from the last batch of RLL drives ever made by Seagate because mine is dated 1990. At the time there were fast and large 50Mb+ IDE and SCSI disc drives that easily outperformed these dinosaurs.
I still use this disc drive from time to time. I have noticed that the controller somehow remembers the drive parameters. So I keep using it on one of my 386 systems as well as on my 486 computer. I haven't been able to connect an IDE drive along with the RLL drive, maybe because I don't know how to see the memory range of the IDE host adapter on the 386/486 computer, but I successfully ran a SCSI disc drive along with this old RLL disc drive. That's the benefit of SCSI being a host adapter, not really a disc drive controller.
I recommend all of you who are interested in old storage media, to spend some time with this aging drive. Although it may not be the best RLL drive out there, it still remains a reliable one and you could easily get the in the mood of those times while playing around with it. Mind the infernal spindle motor noise, that is.