23
Feb
14

Magnetic Tape Storage

Audio Tape

Audio Tape

Tape is probably one of the older mediums for storing data, both for computers and in general. Anyone who grew up in the 80’s will remember the humble audio tape. In my family we all got our own radio combined with a tape player in our early teens, mostly so we could listen to music. We bought ourselves blank tapes and would record music from the radio which was a common practise at the time.

Early micro computers made use of audio tape, mostly because it was cheap and very common. They encoded in audio waveforms in a similar way that modems did later for telephone lines. The disadvantage was that they were incredibly slow, and had to be wound to the start of the program each time to load it. It was very time-consuming! However many collectors have found recently that audio tape has retained more of its reliability over time compared to floppies.

Tape storage didn’t end or begin with the micros however. It was used for many years before in the mainframe world in the form of large reel-to-reel tape drives, where it proved its reliability and storage capacity was superior compared to other storage. People moved away from using large expensive machines such as these so it became important to develop backup and storage solutions for smaller personal machine such as the IBM PC. From here tape drives became an important storage medium for long-term storage of data, distribution of large data sets, and backup copies. It was even used by many Unix workstation suppliers to distribute their operating systems!

Tape Drives

Tape Drives

Here I have a small collection of tape drives that I’ve accumulated over time. The left hand drive is the newest being an Exabyte Eliant 820 which uses 8mm tape that I think was also used in some camcorders. The drive at the top right is an AIT 2 drive which used similar cassettes but a different grade of media. The two remaining drives are DDS drives which are one of the older standards. They used 4mm tapes, I have a cleaning tape and data tape on the table in the foreground. All of these drives used the same technique to store data as VHS.

AIT Drive Internals

AIT Drive Internals

This picture will look very familiar to anyone who has dis-assembled their VCR. You can see the rotating drum that houses the read/write heads. One difference between this drive (the AIT 2) and VHS is that this drive does not have the linear head for erasing or audio. Otherwise it is pretty much a scaled down version of VHS.

DDS Drive Internals

DDS Drive Internals

Here is an overview of one of the DDS drives. You’ll notice it is very similar to the AIT drive in its features, just scaled down for the smaller size tapes.

Wheely wierd

Wheely wierd

Although I did notice the strange wheel inside the drive, I assume it’s for cleaning, although a cleaning tape is usually used for that purpose so I’m unsure of this.

Tape path

Tape path

Here I’ve inserted a tape to show the path the tape goes through this drive. Again it’s almost identical to the path tapes would take through a VHS machine. It doesn’t appear to have the capstan and roller found in audio tape players and VHS.

Unfortunately I don’t have an LTO drive, as they have some of the most interesting internals I have come across. Unlike other tape systems the cassette has only one reel in it. The tape engages a mechanism inside the drive to pull the leader through to a second reel permanently stored in the back of the drive. The heads are then engaged when the leader has wound onto the take-up reel. This is part of the reason LTO drives are quite large compared to other types. These drives can store up to 2.5 Terabytes per tape with the newer drives.

Basic Computer Games

Basic Computer Games

Finally, storage of a different form. I recently bought a book that has 101 games written in BASIC from the late 70’s. Reading its pages is like looking back in time to the days when people used time sharing systems and simple micro computers to play simple games such as these. Frequently these games were distributed in print form, and users had to type them into their machine, making modifications for their machine as they went. You can find an archive of the games themselves here, but I found the book was nice to have because of the illustrations and descriptions of the games.

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3 Responses to “Magnetic Tape Storage”


  1. February 24, 2014 at 9:10 am

    Great post! I’ve never seen the inside of an AIT or DDS drive before, but I was aware that they used the same helical scan technology as VHS. It looks like it’s quite miniaturized although the amount of tape wrap around the head seems to be different.

    Interestingly, the AIT drive has one of those auto head cleaners too – the little bit of squishy white foam on the white plastic arm – it’s likely actuated every load or unload of cassette. This is very similar to that of the VHS “auto head cleaner” but we really don’t think it does much chop. The “swirly” style one might be more effective though!

    It’s interesting because I’ve never owned a tape drive mainly out of economics (very expensive drives with moderately expensive tapes …) – I still remember the QIC/Travan tapes, and I know of LTO. I’ve also known of the even larger ~120Mb cartridges with ferric oxide tape in them, I had one but I threw it out. They were quite sturdy beasts.

    • February 24, 2014 at 10:16 am

      I got most of these drives either with a sun machine or from an old server no longer required. Perhaps the speed of the tape is the reason they don’t need to wrap the tape as far around the heads?

      Pretty much every tape drive standard I know of uses cleaning tapes, so I’m not sure why they have the auto cleaning bits. I didn’t notice the DDS one engaging with a data tape, so that might only engage when a cleaning tape is inserted. I’ll have to try this out.

      I was quite lucky to get the ones I have, but they didn’t cost anything/much at the time because of how obsolete they are. The tricky part is getting tapes for them, I have managed to get enough DDS tapes to use with the Sparcstation 20 for backup, and a cleaning tape. There seems to still be a supply of DDS style tapes available. It may be a reflection of the number of manufacturers, as only Sony seems to make AIT media and Exabyte are the only ones to have made official Exatape media. DDS media on the other hand seems to be made by a wide variety of companies, seems to be significantly cheaper, and even the older types of media are still available.

      I’m unlikely to ever get an LTO drive unfortunately, even old drives are quite expensive. From what I’ve seen it’s cheaper to buy an old server with a drive than it is to get a drive on its own!

      Cheers
      Sparcie

    • February 24, 2014 at 8:27 pm

      I had another look inside the DDS drive and found two things. Firstly that cleaning wheel doesn’t engage when either data or cleaning tape are inserted. I’d imagine that it’s a last resort measure when the heads get dirty. These drives can tell somehow when the heads need cleaning, so it may try that wheel before declaring the cleaning tape necessary.

      Secondly I found the capstan and roller mechanism. See the roller in the tape path nearest the upside down PCB, there is a capstan hidden within a sectioned cyclinder thats hard to see in the photo. There is a motor underneath to drive it.

      I think I can see the same mechanism in the AIT drive. The capstan in near the shaft going across the top of the drive at the right hand side. I figured the direct drive motors on the reel drives may have made the capstan unnecessary for speed control, it seems I was wrong. You’ll note that the roller in both drives is on the opposite side of the capstan compared to audio tape and VHS.

      Cheers
      Sparcie


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