报告题目：Preventing Data Loss When A Hard Disk Crashes 

报告人： Professor Ling San （Nanyang Technological University）

时间：12月9号周日上午10：00-11：00

地点：五教5306

摘要：

Suppose that data is stored on storage devices (like hard disks) in blocks of 7 bits, such as (0,1,0,0,1,1,0). For example, this is the case of the ASCII code used to represent text in computers, telecommunication and other devices. If we store the data on a single device, and this device crashes, all the data stored will be lost. To prevent the loss of data in such an event, a simple solution is to store an identical copy of the data on a second device, so that when one device crashes, the other one still retains a copy of the data. In this scenario, for a 7-bit data, we are effectively storing a total of 14 bits. 

When many devices are available to store the data, there are actually alternative ways to store the data so that the total number of bits to be stored for a 7-bit data is much smaller than 14, and yet the data can still be fully recovered when one device crashes. Underlying one such clever scheme is some simple mathematics that can be understood by high school graduates. 

This is precisely what we shall see in this talk.