by SV3ORA
Introduction
The purpose of this page is to present the different computer data storage media types and investigate their long term reliability, data preserving and immunity to failures due to physical factors. This page ignores issues related to data capacity and media obsolesce and it does not try to compare media based on these properties.
I have decided to write this article after a thought I had of what type of data storage media should I use for my simple, failure immune 4-bit digital computer made out of common TTL chips. I will borrow many information from Wikipedia as long as other websites and papers, so please have this in mind when you read this article, as I am not able to present here the exact sources I have taken the material from.
Types of data storage media
There are four common basic types of computer data storage media: Magnetic, optical, semiconductor and paper.
Magnetic consist of a variety of magnetic media and containers including a range of magnetic tapes such as reels, cartridges, cassettes and disks. They all utilize the magnetic properties of metallic materials suspended in a non-magnetic mixture on a sub-strate. The method of construction and storing the data, point to potential weaknesses of magnetic media.
Strong magnetic fields may alter the media and lead to data loss but this is rare and the media normally has to be in very close proximity for this to occur.
Clean operating conditions and environments will reduce the scope for damage to media and devices.
The high density of storage and the close proximity of device heads to the media mean even small particles such as smoke or other debris can lead to data loss
Poor environmental storage may also lead to oxidation of the ferromagnetic material or problems with the "binding" layer or substrate materials.
Handling and use of magnetic storage media should be minimized to reduce wear, or refreshment cycles implemented to replace media on a frequent basis reflecting the levels of use.
Operating temperature range is very limited.
Optical storage media use laser
light to read from a data layer. A number of different types such as CD-ROM
(Compact Disc - Read Only Memory), CD-R (Compact Disc - Recordable), and DVD-ROM
(Digital Versatile Disc - Read Only Memory) exist.
In CD-ROM the data layer consists of a series of pits in a metallic coating over
a plastic disk. A clear acrylic coating is applied to the metallic layer to
protect it from light scratches and corrosion. CD-R employs a dye layer which is
light sensitive as the data layer.
The use of light sensitive dyes means CD-Rs are less stable than CD-ROMs as archival media.
As with magnetic media there is considerable diversity in practice and production of CD-R and care is needed in selecting high quality media.
Optical disks are an increasingly popular method of storage. The device reader is not in contact with the disk and mechanical failure is less likely to lead to data loss than damage to the disk itself through poor handling or storage.
Operating temperature range is very limited.
Magneto-optical disc storage is a combination of optical and magnetic technologies and it uses the magnetic state on a ferromagnetic surface to store information. The information is read optically and written by combining magnetic and optical methods.
Semiconductor memory uses semiconductor-based integrated circuits to store information. A semiconductor memory chip may contain millions of tiny transistors or capacitors.
In DRAM and SRAM, uninterrupted electric power must be supplied or the contents of memory will be lost.
ROM (Read only memory) can be read but not erased or overwritten. Instructions and programs in primary storage can be permanently "burned in" to the storage cells during manufacturing.
Flash and EEPROM has a finite number of program-erase cycles.
Operating temperature range on all above is limited to -55C to +125C on best case mil-spec semiconductors.
Paper data storage is a form of data storage, consisting of strip of papers or paper cards in which holes are punched to store data.
Longevity. Although many magnetic tapes have deteriorated over time to the point that the data on them has been irretrievably lost, punched tape can be read many decades later, if acid-free paper or Mylar film is used. Some paper can degrade rapidly.
Human accessibility. The hole patterns can be decoded visually if necessary, and torn tape can be repaired (using special all-hole pattern tape splices). Editing text on a punched tape was achieved by literally cutting and pasting the tape with scissors, glue, or by taping over a section to cover all holes and making new holes using a manual hole punch.
Magnetic field immunity. In a machine shop full of powerful electric motors, the numerical control programs need to survive the magnetic fields generated by those motors.
Ease of destruction. In the case of cryptographic keys, the inherent flammability (sometimes enhanced by using flash paper) of paper tape was an asset. Once the key was loaded into the device, or if it may fall into enemy hands, the paper tape was simply burned.
Media life
Media should be refreshed on a regular cycle within the lifetime for archival
storage identified by the manufacturer or independent sources. Sample generic
figures for lifetimes are given below.
D3 Magnetic tape: 1 - 50 years
DLT magnetic tape cartridge: 1 - 75 years
CD/DVD: 2 - 75 years
CD-ROM: 3 months - 30 years
Punched paper media: Depends on quality of paper, but in general more than
magnetic media.
The best of all media as far as concern media life and data preservation?
In my research about what type of data storage media should I use for my simple, failure immune 4-bit digital computer made out of common TTL chips, I thought of all the above considerations. If data capacity can be kept low, punched systems may be of great interest.
The greater disadvantage of punched cards and tapes, is the paper medium which can be easily damaged. This disadvantage does not refer to the punching technology used, but to the medium where the punches have been made onto. If we could punch holes on another medium other than paper, then we could ensure a much much greater media life and consequently data preservation.
Aluminium is the third most abundant element, and the most abundant metal, in the Earth's crust. It is soft, durable, lightweight, ductile, malleable and non-ferrous metal. It is theoretically 100% recyclable without any loss of its natural qualities. It is almost always alloyed, which markedly improves its mechanical properties. Most importantly, it is remarkable for its ability to resist corrosion and it can be easily found on metal shops in different shapes, including different diameter square and cylindrical bars.
My radio amateur experience has shown me that whatever is made out of metal, like those WW2 military radio equipment, lasts much longer. The archaeological findings also shows us that whatever is engraved on non-corrosive metals or other hard material, lasts millions of years. The idea for ultra long lasting media, is to drill holes onto an card made out of a square piece of aluminium metal.
Disadvantages
Non-flexible, it cannot be rolled like punched tapes. Multiple cards should be used in sequence if more data needs to be read.
Difficult to write data onto. Drilling must be made.
Much more weight than paper.
Read only, but ability to easily correct errors in future by literally drilling new holes or by taping over holes.
Advantages
Ultra wide operating temperature, ranging from near absolute zero to +660.32C where the melting point of aluminium is. Unless you drop the aluminium card into a volcano or a metals foundry, it will survive.
Human accessibility. The hole patterns can be decoded visually if necessary. Editing text can be achieved by literally drilling new holes or by taping over holes.
Magnetic field immunity. In a machine shop full of powerful electric motors, the numerical control programs need to survive the magnetic fields generated by those motors.
Longevity. As long as sufficiently thick aluminium bars are used as cards, data can never be lost due to inflection or accidentally cutting of the metal bar. It could last for hundreds or maybe millions of years.
Ultra long reading cycle. The same card can be read millions, maybe billions of times, especially if an optical reading mechanism is used.
Completely waterproof. Aluminum bars can be dropped inside a box full of water or left outside in winter without corroding or get damaged.
Radioactivity and X-ray immunity. In a nuclear or X-ray rich environment, the numerical control programs need to survive the radioactivity generated by these sources.
Immunity to dust. As long as the holes on the card are kept clean, dust will not be a problem. Very dusty holes can be easily cleaned using a toothpick, a piece of wire etc, without affecting the medium. The larger the holes on the card, the more difficult is to get dusty, but the size of the card gets bigger.
All the above, may give you an idea of why metal punched cards could be far superior in extreme environment surviving in comparison to the fragile media we use today for data storage. Of course, I have completely ignored the data capacity issue on this article, which is indeed ultra low on punched cards. But if data capacity does not need to be high and media surviving is more important, one should consider this idea.