Boffins double mobile phone memory

US computer engineers have developed compression technology that effectively doubles the usable memory on embedded systems such as mobile phones and cameras without any changes to hardware or applications.

The team from Northwestern University and NEC Laboratories America said that the memory boost can be made by modifying the operating system software alone.

This breakthrough, the result of two years' research, is featured in NEC's Foma N904i handset which hit the shelves in Japan this summer.

"All the things you do with a cellphone or PDA require memory," said Robert P. Dick, assistant professor of electrical engineering and computer science in Northwestern's Robert R. McCormick School of Engineering and Applied Science.

"The technology we have developed automatically takes data and reduces it to less than half its original size without losing any information while the embedded system is running.

"It is like putting twice as much memory in the phone without increasing its cost or power consumption."

NEC Labs researchers conceived the concept of integrating compression technologies into the operating system itself in early 2004 to provide compression as an operating system service.

The idea was transparently to compress and decompress selected regions of memory (code and data) to reduce the memory footprint of embedded applications.

NEC Labs entered into a partnership with Northwestern to jointly develop the idea. The team consisted of Dick, his first doctoral student, Lei Yang, and Haris Lekatsas and Srimat Chakradhar from NEC Labs America.

Yang, with help from the other team members, led the design of Crames (Compressed RAM for Embedded Systems), a software-only compression infrastructure technology that has minimal performance and power consumption penalties.

The team's approach was to divide the memory in the system into two different regions, one regular and one where the data is greatly compressed.

A very simple example of data compression is converting a list of 50 individual 'A's into the phrase '50 As', which takes up less space but communicates the same information. This can then be converted back to an identical copy of the original text.

When an application needs data from the compressed region the hardware pauses the software, the operating system accesses the data, uncompresses it and puts the data into the regular region where the application can access it.

The application continues running without ever knowing that the data it needed has been compressed.

Crames uses an existing data compression algorithm, called LZ0. In ongoing work, Yang has developed a compression algorithm that is more advanced, taking advantage of recently seen patterns in the data.

Her algorithm is twice as fast, allowing "negligible reduction" in performance and battery life even when 60 per cent of an embedded system's memory is removed.

The algorithm works for a wide range of applications and may be used in future NEC phones.

Northwestern and NEC have filed a joint patent application on the Crames technology.