General-purpose multi-access computing systems with files stored on random-access devices require that these files be protected. If the total on-line storage is inadequate there is a need for wellorganized off-line storage. This thesis discusses the management problems involved in handling backup and archive copies of files. In Part I we review what a number of systems, including the Edinburgh Multi-Access System (EMAS), have achieved. We also consider the influences of hardware and other forms of computing system. In Part II we return to EMAS and propose a design and an implementation to provide comprehensive facilities, for backup copies of files and recovery of them, and also for archive storage.

Recent years have witnessed a proliferation of flash memories as an emerging storage technology with wide applications in many important areas. Like magnetic recording and optimal recording, flash memories have their own distinct properties and usage environment, which introduce very interesting new challenges for data storage. They include accurate programming without overshooting, error correction, reliable writing data to flash memories under low-voltages and file recovery for flash memories. Solutions to these problems can significantly improve the longevity and performance of the storage systems based on flash memories. In this work, we explore several new data representation techniques for efficient and reliable data storage in flash memories. First, we present a new data representation scheme—rank modulation with multiplicity —to eliminate the overshooting and charge leakage problems for flash memories. Next, we study the Half-Wits — stochastic behavior of writing data to embedded flash memories at voltages lower than recommended by a microcontroller’s specifications—and propose three software- only algorithms that enable reliable storage at low voltages without modifying hard- ware, which can reduce energy consumption by 30%. Then, we address the file erasures recovery problem in flash memories. Instead of only using traditional error- correcting codes, we design a new content-assisted decoder (CAD) to recover text files. The new CAD can be combined with the existing error-correcting codes and the experiment results show CAD outperforms the traditional error-correcting codes.