Data For Eternity (Part 3)

10/25/2012 9:16:09 AM

Description: The layers of the GlassMasterDisc

The actual data layer comprises glass into which slots are etched. The reflection layer made of metal ensures that the disc is readable in any BD or DVD drive.

Production of a glass disc

The production process has more to do with the production of chips than with the normal burning of a disc. Therefore it is also carried out in a dust-free room.

1.    Put on photoresistor

Description: Put on photoresistor

A layer of lacquer is applied on the glass disc.

2.    Allow to harden

Description: Allow to harden

The lacquer serves as a data layer and must first be hardened.

3.    Laser writes data

Description: Laser writes data

A laser burns bits into the lacquer. It is removed in the exposed areas.

4.    Carry out dry etching

Description: Carry out dry etching

The data structure is transferred with the help of lacquer mask using ion bombardment.

5.    Apply metal sheet

Description: Apply metal sheet

Metal alloy is added by cathode sputtering.

6.    Stick disc

Description: Stick disc

The disc is sealed with a second glass layer using UV glue.

Memory vault: flash protection

Sandisk offers a 100-year guarantee on the flash device preserved with corrosion protection. In purely theoretical terms, it could last for 1,300 years.

Data storage is moving away from discs and magnetic plates in the direction of solid-state flash in the form of USB sticks, memory cards and SSDs. These data storage media do not have a good reputation since flash cells wear off after a certain number of read/write operations. However, this does not matter in the case of long-term archiving, when data will be written only a couple of times and then be read much later. Sandisk has launched a flash memory product for this application called Memory Vault. In the beginning, it allows the in-built controller to overwrite and delete data. The Vault switches to a read-only mode after a certain number of write/delete cycles. Sandisk says nothing about when exactly this happens but the user will notice it due to the increasingly fast blinking of the in-built LED light. This mechanism prevents exhaustion of the flash cells, but they are still exposed to natural decay. The decay rate depends strongly on the storage temperature.

Description: 16GB.
Sandisk has launched the Memory Vault in two versions: It costs $49.99 for 8GB and $89.99 for

Sandisk has launched the Memory Vault in two versions: It costs $49.99 for 8GB and $89.99 for 16GB.

Flash lasts longest when stored in cool places

A flash cell is principally a transistor with an additional component: the floating gate which stores electrons. The voltage created ensures that the electrons drift from the channel through the isolating oxide gate into the floating gate or out again in case of a deletion operation. The quantity of electrons stored in this way determines the bit value of the flash cell. Whether or not electrons tunnel through the oxide gate is determined by the energy supply. Besides current, even heat can trigger electrons tunneling even though the flash memory is inactive. Flash lasts very long at room temperatures before the effect becomes apparent.

In order to test the durability of flash cells in the Memory Vault, Sandisk has increased the temperature tolerance to 125°C and measured the point at which the flash memory loses its data. It goes relatively smoothly at this temperature: after almost 350 hours, data security could no longer be guaranteed for the Vault. The lifespan of 105 years was established when scaled down at a still-uncomfortable storage temperature of 40°C since the proportion between temperature and lifetime is exponential and not linear.

Officially, Sandisk advertises this product with a 100 year lifespan but if one converts the test result into storage at room temperature (20°C), the Vault should conserve its data for up to 1,300 years. Other external factors play a role in case of these calculations, since even corrosion affects the circuitry of the Vault. Sandisk has coated the memory chips with a special additional protection layer. The measures are reflected in the price: an 8 GBVault costs approx. $51 and the 16GB variant costs $93 - durability doesn't come very cheaply.

The flash cell as data storage

If voltage is created at the control gate, electrons drift from the chan­nel in the floating gate and are stored. If you apply a voltage with re­verse polarity, they flow out again.

Description: The flash cell as data storage

The flash cell as data storage

Durability of flash

A test according to the JESD22-A117B industrial standard deter­mines when flash memory breaks down. It is based on the fact that the lifespan of a cell decreases exponentially depending on the temperature.

Description: Durability of flash

Durability of flash



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