Thanks to one of my friends at the university, while I was out of action due to my ankle, he managed to save me quite a few “old” things that were thrown out. One of them was this – a Fujifilm DLTtapeIV Cartridge.
Digital Linear Tape, or DLT for short, was a backup tape format first developed by Digital Equipment Corporation and later bought by Quantum. This system used a half-inch tape inside a cartridge with a single spool, with the take-up reel being inside the drive itself. The leader is specially formed so that the drive can “catch” the beginning of the tape, and thus, the tapes cannot be ejected without first being rewound. This format evolved through multiple generations, and all of the technical details are nicely gathered in the Quantum DLTtape Handbook (well worth a read, at least the first 87 pages or so).
In many ways, this format pioneered the reliability which was a hallmark of simple mechanisms, minimal handling guides, and fixed head linear recording, and was very much emulated by the open, less-controlled, Linear Tape Open (LTO) format.
Such tapes don’t normally land in my hands as many home users didn’t resort to tape backup, and corporations usually carefully dispose of their tapes. In this case, I managed to get several “still new, unused” condition tapes. The tapes themselves were probably fairly pricey and dates back to around 1994-1999.
Unfortunately, I didn’t have any drive to use them with, but it’s worth a close look and a teardown.
The cartridge comes in a translucent plastic box, with two large rectangular raised parts which engage with corresponding depressions in the bottom of the next box for stackability. The box opens on the left edge to reveal the cartridge. The cover itself has a lip along the edge, likely for dust-control.
The front cover itself gives a good amount of information about the cassette itself.
The cassette media itself uses “ATOMM” technology, which implies it is a Metal Particle type layer. The cassette itself was Made in Japan – there were only a handful of manufacturers at the time. The tape is claimed to be 12.65mm, with a capacity of 40/70/80Gb depending on which DLT drive is in use (due to different recording formats). All of these capacities are claimed at a 2:1 compression ratio, the native capacity is just 20/35/40Gb.
The inside features strict information about storage and use of the write protect tab. On the right side, are peel off perforated card segments which can be written on and slipped in a corresponding notch in the cartridge for labelling purposes.
The cartridge itself, as characteristic of the DLTtapeIV format, is in a chocolate brown colour. It’s also roughly square in shape.
There are no clear windows – you know the tape has to be fully wound on the cartridge if it’s ejected! The bottom reel drive has a very interesting shape, which has many many points of engagement. There’s a hole at the bottom which one of the reel lock disengagement points.
The top of the cartridge has another hole which corresponds to the second reel lock disengagement point. The left part has a pull-down latch which opens the tape flap door. Visible is the leader tail which is used by the drive to engage with the tape. The reel lock teeth is just visible through the slot at the bottom.
The bottom edge of the cartridge has the labelling area – the piece of cardboard can be inserted through the slot and slid into the rails. A captive write protect mechanism slider is visible, when the orange is visible, the cartridge is write protected. This also controls an indent on the right side of the cartridge for write-protection detection, as can be seen below.
The final side of the cartridge is the left side – it’s not really interesting …
Since I had several cartridges, I didn’t mind sacrificing one in the quest of knowledge. Luckily, as the cartridge was held together by screws, opening it is as simple as undoing the Phillips head screws on the bottom. The cartridge practically springs apart.
The top of the cartridge is seen on the left side. The door and the two spring-loaded reel lock mechanisms are visible. The spool is on the right side, with the finely-teethed reel lock plate visible. The spool itself is sprung against the top lid with a circular spring, which rides on a precision smooth-running bearing (likely, ball bearing, similar to that on computer fans).
The tape is protected by a specially formed leader – this is the initial segment. The leader is specified to be 18 inches in length, and is enough to fully wrap around the tape (thus, keeping dust and environmental impact upon the thin tape to a minimum). The leader itself is quite thick and sturdy compared to the metal particle tape.
Here, we can see the leader attach to the metal particle tape with splicing tape. This implies that the recording surface is actually wound recording side face down which is quite smart!
Well, looking at this can you think of any other common half-inch tape format?
I’ll give you a moment …
… if you’re anything like me, at this point, it’s where you go eureka! Of course! VHS!
The first thing I was thinking of was “how much tape is on a DLTtape IV cartridge?” which was very quickly answered by the DLT Handbook linked earlier – 1800 feet. That’s a lot of tape. In fact, a PAL E-300 5-hour cassette only has 1427 feet of tape. Visually judging, the tape seems to be spooled on a reel with a larger hub, so it’s got to be very very thin tape.
The next thing I asked myself was “how good of a VHS tape would DLTtape IV metal particle tape be?” Initially, I thought it might be good because of the high quality of tape required for high data densities, but I also realized it would probably not work well since metal particle tape can be more abrasive to heads, and helical scan recording causes high tape-to-head speeds. The other problem was that metal tape has higher coercivity than chrome dioxide and ferric formulation cassettes, which might mean the VHS deck may not have a strong enough magnetization to record to the tape properly.
The only way to know for sure, is to try it! Don’t do this at home – you could cause yourself some damage to your VHS deck if you don’t do this right!
So, how does one wind a DLT tape to a VHS spool? Well, first you grab a VHS you don’t care about (in my case, a spare Q-stores E60 cassette with large spools, makes winding a bit quicker although you can’t wind quite as much) and clip off the tape, leaving leader intact. Then you “splice” together (with sticky tape, as I didn’t have splicing tape) the tape to the leader … and begin winding …
Yep. By hand. But uh-oh … the DLT handbook warned me of this …
That’s the beginning of tape “hole”. This hole indicates the beginning of the real recording – the prior tape is used for calibration and directory recording. So then, I disposed the tape and then respliced after this hole. For reference, there’s an end of tape hole which is exactly the same, but is 610cm from the end of the tape. The tape isn’t actually held to the DLT hub by anything – it’s just wrapped on top of itself and held by tension.
After a few hours of winding, I got this …
I eventually threw out the remaining tape as I unwound it to find out what’s at the end (yeah, that wasn’t worth the effort).
When spliced back to the other VHS reel, and placed into a cassete shell, it turned out to be an E-209! That’s right – just one minute short of three and a half hours on reels which normally hold no more than an hour and a half of VHS tape. That shows just how “thin” and fragile DLTtape IV is.
Speaking of fragile … the thinness of the tape causes it to curl around the edges, and that’s pretty normal of most thin metal particle tapes. It’s also exactly shiny, and seems very smooth, but how it treats the heads of my VHS deck is another story … the tape wasn’t designed for helical scan recording, so it might not work very well. Maybe it’s too thin to achieve reliable head-to-tape contact, aside from the coercivity issue.
The answer: as expected, it didn’t work so well. The playback of a static menu from a DVD recorded to the tape was very noisy chroma wise and had many dropouts. The noise in the chroma, and the entire chroma dropout during tracking suggests the RF signal level on the tape was very low, indicating it wasn’t recorded well into the tape. At least, now we know …
So, uh, don’t use DLTtape IV as a VHS tape? *chuckles to self*