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An overview of Microsoft Project Silica and its archive use

Microsoft's Project Silica stores data in silica glass, similar to the crystals in 'Superman' films. In fact, 'Superman' already played a major role in the forward-looking project.

The 1978 Superman movie has found a home in a piece of quartz glass that's 2 mm thick and 75 mm square in area -- about the size of a drink coaster.

A digital version of the movie was stored in the glass as the first proof of concept for Project Silica, a Microsoft Research project that develops advanced archival storage technology, specifically for the cloud. Microsoft Project Silica uses ultrafast laser optics to store the data, as well as microscopy and artificial intelligence to read the data. It provides a storage medium that can potentially last thousands of years without degradation.

What is Microsoft's Project Silica?

Today's storage technologies will soon reach their practical limits as demand for long-term cloud storage continues to grow to unprecedented levels. Most cold data is currently stored on magnetic tape, optical disks, HDDs and, to a lesser degree, SSDs. However, none of these are cost-effective platforms to handle the vast amounts of archive data that will live in the cloud. Each one was created before the cloud existed and was designed to support multiple uses. No storage technology was built specifically to store cold data at cloud scale.

The cloud requires a reassessment of large-scale storage systems and what it will take to meet the challenges ahead. Many believe the time has come to create new systems designed from the ground up specifically for the cloud. This is where Microsoft Project Silica comes in. It explores whether quartz glass can serve as a practical medium to store cold data in the cloud for long periods of time and replace the other media altogether.

Project Silica is part of the broader Optics for the Cloud project, a Microsoft program to advance the adoption of optical technologies in the cloud. Most of the work on Project Silica occurs at Microsoft Research's Cambridge lab in the U.K., where a team of physicists, electrical engineers, optics experts and researchers with storage backgrounds are building a completely new type of storage system. To carry out this project, Microsoft partnered with the Optoelectronics Research Centre at the University of Southampton, where scientists already proved the ability to use laser-writing technologies to store data in glass.

Project Silica researchers have set their sights on silica glass because of its durability. They've baked it, boiled it, microwaved it, demagnetized it and scoured it with steel wool, and after all that, they were still able to read the data. Quartz glass does not require expensive environmental management such as temperature and humidity controls, and it can retain data for thousands of years without experiencing bit rot. It avoids the costly cycles of rewriting data to next-generation storage media. Quartz glass is also plentiful and relatively inexpensive compared to other media, making it well suited to store great amounts of cold data indefinitely.

Microsoft's Project Silica team focuses solely on building storage for archiving data at cloud scale. It's not trying to provide consumers with new ways to run their personal computers or watch movies at home. The team is concerned only with developing a storage medium that can handle large amounts of cold data that's seldom accessed, whether every few months or every few years.

How does Project Silica work?

Project Silica builds on earlier efforts by researchers at the University of Southampton, where they demonstrated the ability to store data in fused silica, a non-crystalline form of silicon dioxide. It's found in quartz crystals and sand, among other materials. Their first success was in 2013, when they stored a 300 KB text file in fused silica glass, which they dubbed 5D memory crystal.

Microsoft's Project Silica team focuses solely on building storage for archiving data at cloud scale.

The researchers refined their design and put major documents on silica disks less than an inch in diameter. These included Isaac Newton's Opticks, the Magna Carta and the United Nations' Universal Declaration of Human Rights. It wasn't until 2018, however, that the press took serious notice, when a SpaceX rocket named Falcon Heavy launched from the Kennedy Space Center in Florida. The rocket, which is now on an orbit around the sun, carries Elon Musk's red Tesla Roadster. In the car is a 5D memory crystal that contains Isaac Asimov's Foundation series of science fiction books.

The Microsoft Project Silica team uses similar technologies as those employed by the University of Southampton researchers. When encoding data, the team aims a femtosecond laser at the quartz crystal -- the type of laser found in Lasik eye surgery. The laser etches nanoscale gratings (voxels) into the glass at various depths and angles. This requires that the laser emit ultrashort optical pulses, which permanently change the structure of the glass. It creates a three-dimensional voxel layout of the data.

Project Silica encodes the data by changing the strength and orientation of the laser pulses. It creates a series of unique voxels with different depths, sizes and grooves. The laser creates voxels in a single layer by focusing the beam at different positions across an X-Y plane. The laser creates voxels in different layers by changing the beam's focus depth within the glass. A piece of glass that's 2 mm thick can support more than 100 layers of voxels.

Each voxel creates a condition known as form birefringence, a characteristic in which the voxel exhibits refractive properties different from the surrounding silica, which essentially changes the way light travels through glass. When polarized light interacts with a voxel, nanometer shifts occur in its electric field. The range of the shift is referred to as the voxel's retardance. There's also a change in the light's polarization angle. These two birefringence properties -- retardance and angle change -- make it possible to encode multiple bits per voxel. In addition, once the voxels are created, the properties remain stable for the lifetime of the glass.

Why Superman serves as a good proof of concept

Warner Bros., which owns the Superman rights, has an enormous film and television library. It looks for ways to protect its assets against everything from floods to solar flares without worrying about issues such as extreme temperatures, humidity or the need to refresh media.

The storage under development at Microsoft Project Silica could prove an ideal method to archive the Warner Bros. library in a way that's practical, inexpensive and safe, which is why the Superman test was so important. The Project Silica team stored the film in its entirety in a single piece of glass and then read it out successfully. That was back in late 2019. It represented a significant milestone in the Project Silica effort and provided impetus for moving forward with its research, an effort that continues to this day.

Data is read from the glass by measuring the two birefringence properties. A type of microscopy employs a camera and special optical components, similar to a microscope. An illumination arm passes a beam of light through the quartz glass and optical components, with the beam polarized to one angle. The camera detects the changes in the light's polarization as the beam passes through the optics and quartz glass. To read different layers in the glass, the optics focus at different depths.

Microsoft Project Silica also uses machine learning algorithms to interpret the camera's voxel images. The algorithms require four measurement images and four background images to decode the patterns created by the polarized light shining through the glass. Project Silica also uses deep learning and neural network technologies to help address potential variabilities and noise that come with reading the data. In this way, dealing with voxel complexities becomes an offline operation, separate from the process of physically reading the data.

What is the future of glass storage?

The Superman test case demonstrated it is possible to use crystal glass to store and retrieve archival data. But researchers still have a long way to go before data can be written and read at speeds fast enough for practical application. In addition, they need to achieve greater densities. For this, they must be able to encode more bits per voxel and read voxels through more layers. Researchers also face challenges around measuring birefringence. Noise increases significantly when the lateral spacing between voxels decreases and the number of layers increase.

At this point, there is no clear timetable for when Microsoft's Project Silica efforts might be ready for large-scale, production-ready storage systems. There have been some suggestions of viable systems within a decade, but that is little more than conjecture. What's clear is that storage solutions are needed to handle the anticipated growth in data. Microsoft Project Silica aims to address at least part of those needs by targeting cold storage requirements in the cloud. Whether glass storage might one day be used for other purposes is unclear, but, clearly, it has potential to archive large amounts of data.

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