Network Bulletin No.: 11-20

Date: September 30,2011

   Subject: Reliability of USB flash memory cartridges

Network libraries may purchase USB flash-memory cartridges that are compatible

with the NLS digital talking-book player from Northstar Industries, the NLS contract


The technology used to manufacture the memory in the cartridge has changed several times since the first cartridges were produced. The consumer electronics industry has required higher memory capacities, and to meet that need manufacturers have reduced the size of the individual memory cells. This size reduction affects the durability and long-term reliability of data stored on the flash-memory cartridge.

The multi-level cell (MLC) technology used for the first NLS cartridges permitted the memory to have an endurance often thousand write cycles. As the memory density has increased, the durability has dropped to one thousand write cycles for the current cartridges.

The Engineering Section believes that further reductions in endurance may jeopardize the integrity of the data on NLS cartridges, which are specified to be error-free after ten years of storage. Therefore, as of September 2011, most new books will be duplicated onto 256MB single-level cell (SLC) memory, which has very high reliability and write-cycle endurance. The 256MB SLC memory is less expensive than the 2GB MLC memory currently being used and is of sufficient size to accommodate all but the largest books.


Northstar will make the 256MB SLC cartridge available for network library purchase. Northstar will also continue to make higher capacity cartridges available, but network libraries should take into account the reduction in endurance. If cartridges are rewritten less than seven hundred times and if data is to be stored on the cartridge for less than a few years, the use of cartridges with the newer MLC memory should not pose any problem.

For more information contact: Michael Katzmann Chief, Materials Development Division [log in to unmask]

2 re information contact: Michael Katzmann Chief, Materials Development Division [log in to unmask]