Contents - Previous - Next

10.2 Format-specific preservation costs - a first attempt

Dietrich Schüller, Phonogrammarchiv, Vienna

Cor Doesburg's paper (see above) impressively shows that storage costs, if we compare analog tape even with R-Dat, do not significantly decrease with the size of carriers if we include the costs of the entire archival operation into our calculation. Let us take now one step further in trying to explore the preservation costs as a variable of the storage format. Because storage costs depend on the size of the carriers, preservation costs have to take into account the costs of (subsequent) re-recordings onto new carriers depending on their respective life-times. To get an idea about the influence of the life-time of carriers in such a calculation, two different carriers with differently assumed life- times shall be compared.

As R-Dat is not yet recommended for long-term storage let us compare analog magnetic tape, running at a speed of 19CM/S, with a hypothetical "X-Format": this X-Format would have greater data density than professional analog magnetic tape thus using less shelf space per stored hour. As a consequence of increased data density we assume, however, a shorter life-time. Let us, for the X-Format, make the following assumptions:

Size (incl. box): 110 x 70 x 17mm (like a compact cassette)

Recording capacity 1 hour

Price: Austrian Schilling (ATS) 100.--

Life-time 20 years

The respective figures for analog magnetic tape (730m) are:

Size (incl. box): 275 x 275 x 17mm

Recording capacity: 1 hour (19cm/s)

Price: ATS 250.--

Life-time: 50 years (optimistic, but not unrealistic).

To arrive at comparable storage costs, we have to define a storage unit: (Note: All figures and prices are taken from the actual situation of the storage vault of the Phonogrammarchiv in Vienna.)

It measures 5 x 5 x 2,5m, and is equipped with mobile shelves which occupy a space of 4,2 x 4 x 2,2m, leaving an aisle of lm across for general access and a "moving aisle" of 0.8m. Shelves are arranged to take up a maximum of carriers, leaving - on the other side - enough space to manually handle the carriers. (It has been explained in the Joint Technical Symposium, 1988 that there is a non-linear relation between the size of the carrier and the totally occupied storage volume. As certain dimensions - like the aisle, or the empty space to get hold of the carriers, etc. - cannot be diminished beyond functional needs, there is, with reference to the totally available storage volume, an increasing percentage of empty space along with a decreasing size of the single carrier.)

The storage area is airconditioned and - for ultimate security - equipped with an automated halon fire extinguishing plant; a fire detection and alarm plant is installed in the area around the storage vault wide enough for early alarm.

The annual storage costs are determined by the following factors:

1. The rental for the room: office space with the necessary mechanical adaptation in an appropriate area is available in Vienna for ATS100.--/month. 25 x 100 x 12 = ATS30.000.-- rent/year.

2. Air conditioning, including amortisation of equipment is calculated to be ATS10.000.--/year.

3. Mobile shelves for analog tapes would cost ATS250.000.--, their life-time can be expected to be 25 years, annual costs therefore are ATS10.000.--. The X-Format, however, needs more sophisticated shelves: the costs are estimated to be at least twice as much.

4. The costs of the fire detection and extinguishing plant is ATS250.000.--, the life-time again 25 years, annual costs therefore ATS10.000.--.

5. Annual maintenance costs for mobile shelves and security plants are ATS20.000.-.

The annual storage costs per recorded hour are determined by the storage capacity of the unit depending upon the size of the respective carrier. Mobile shelves as described above can take up 18.500 hours of 19cm/s tape, while they will house as much as 155.000 hours in the X-Format.

Thus the annual storage costs/rec. hour are the quotient of the expressed sum of the annual costs, divided by the storage capacity expressed in recorded hours:

  Tape X-Format
Rental storage area ATS 30.000 30.000
Air conditioning ATS 10.000 10.000
Mobile shelves ATS 10.000 20.000
Security ATS 10.000 10.000
Maintenance ATS 20.000 20.000
Total ATS 80.000 90.000
Storage capacity: rec. hours ATS 18.500 155.000
Annual storage costs/rec. hour ATS 4.32 0.58

Looking at this calculation so far, there would be an enormous argument in favour of the smaller carrier.

But let us calculate now the preservation costs, which take into account the life-time of the carriers and the costs of re-recording. To make the costs comparable for formats of different life-time, they have to be expressed in annual costs/rec. hour. These are determined by:

1. The price of the carriers/rec. hour, divided by the life-time
2. The annual storage costs/rec. hour.
3. The costs of re-recording/rec. hour.

This latter category needs to be explored. Re-recording costs are determined by the following time/cost factors:

Transport of carriers from the shelves to the copying plants.

Copying of old carriers onto new ones; for ultimate fidelity this process has to be done in real time.

Re-labelling of new carriers and boxes.

Documentation of the re-recording process.

Transport of new carriers back to the shelves; depositing of old carriers according to the respective preservation policy.

Maintenance and amortisation of copying equipment.

Under the condition that all old carriers can be replayed in their original fidelity (this means that they do not require additional efforts to restore the original signal due to deterioration) and the existence of several copying plants to work in parallel, it can be assumed that one operator will be able to handle not more than three carriers per hour. That means that re-recording, in the case of one-hour-carriers, will consume at least one third of their playing time. One hour of manpower including equipment costs can be calculated to be at least ATS600.-- which brings us to re- recording costs of ATS200.-- per carrier (=recorded hour in our example). The annual re-recording costs, depending on the time of the various carriers are therefore:

200 : 50 = ATS 4/Year/rec. hour for tape
200 : 20 = ATS 10 ar c. hour for the X-Format

The annual preservation costs/rec. hour therefore are:

  Tape X-Format
Material/year ATS 5.-- 5.--
Storage/year ATS 4.32 0.58
Re-recording/year ATS 4.-- 10.--
  ATS 13.32 15.58

From this example we learn that preservation costs cannot seen by looking at the costs of space alone. The annual costs the material and re-recording have to be included as impor factors. In our example both factors have been assumed quite in favour for the X-Format, still total X-Format's costs are higher than those of 19cm/s tape. A storage plant of that size would also take up 17.160 1000m-tapes (300 x 300 x 17mm) with a playing time of 80 min at 19cm/s or 40 min at 38cm/s. The total storage capacity would then be almost 23.000 hours (19cm/s) bringing storage costs down accordingly. The re-recording costs would also decrease on the side of manpower, as these are dependent upon the number of carriers/rec. hour, but slightly increase on the hardware side due to the the higher amount of equipment necessary. For 38cm/s tape storage costs would double, re-recording costs not quite, as in our example only two copying plants are necessary for continuous work. Different assumptions will lead different results, our example only intends to demonstrate order of magnitude of the various cost factors.

If we finally combine our argument with that of Cor Doesburg and include the costs of the total archival operation into calculation we learn that the size of the carriers is - in terms of overall costs - negligible.

Contents - Previous - Next