If you are younger than a certain age, RLL probably doesn’t mean much to you. Old consumer-grade hard drives used MFM (modified frequency modulation like a floppy disk uses) and soon went to IDE (integrated drive electronics). There was a brief period when RLL (run length limited) drives were the way to get a little more life out of the MFM technology. [W1ngsfly] has an RLL drive on his bench and uses his scope and some other gear to put it through its paces. You can watch over his shoulder in the video below.
The hardware interface and drive are the same for an MFM and an RLL drive. However, an RLL-aware controller can pack more bits on the same platter by using the newer modulation scheme. Some older disks were good enough for MFM but too sloppy to successfully take an RLL format, but — in theory — any MFM drive could be an RLL drive and vice versa.
Interestingly, modern drives still use RLL internally. You just don’t need to know that anymore. For that matter, classic MFM was a type of RLL, but no one called it that.
The basic idea is that long runs of a single bit play havoc with magnetic recording devices. RLL ensures that there will be a certain number of transitions between 1s and 0s over a period of time, regardless of the actual data. Literally, there is a limit to how many bits can “run” together, hence the name.
It sounds like [w1ngsfly] has spent a lot of time working with hard drives. He talks about pulling platters and putting them back in and it is obvious he understands the low-level protocol used in this old Seagate drive.
Even if you don’t care about retrocomputing, it is really interesting watching someone this knowledgeable about anything put it through its paces.
Those old drives seem simple now, but they didn’t back then. These days, you might prefer to emulate these old drives.
I used to have a MFM hard drive, 5MB 5.25″ FH drive. I got it from dumpster diving when a company started clearing out obsolete drives and parts.
Beastly drive was noisy as well.
“Some older disks were good enough for MFM but too sloppy to successfully take an RLL format,”
I bought a used 8088 based luggable in the early 1990s.
It had a 10Mb drive that the seller had boosted to 20Mb.
I was not happy about that, but I’m not one to overclock a processor either.
Been around the computer scene long enough to recall what RLL stood for without reading the article. ;-)
I praise your wonder but I don’t share it. Old school stuff was positively a nightmare to set up when new. For a time between formal 9’to 5 jobs I set up hardware for clients and well maybe it was not a nightmare but labor intensive. I mean for every peripheral in every PC you had to configure IO addresses, IRQs and whatnot via DIP switches in every board and on top of that to watch it for conflicts due to two things trying to use the same address or IRQ. Then there was the problem of wiring them all together and setting up a server (Novell Netware was the weapon of choice). You had a choice of thick or thin Ethernet (always remember to put a terminating resistor on every end of a segment) or token-ring or something more arcane like RS-232 for Xenix systems.
I even built my own interface between one such Xenix machine and a new phone switch for an hotel and I had to bring the wife onboard since I can’t solder worth crap. Good times, the accountant let me sign the restaurant checks; free food!
Did I enjoy it? Hell yeah. Would I do it again? Hekkk no.