Just a year after IBM scientists set a previous hard disk storage record, they claim a new one--surpassing 10 billion bits per square inch. At the new density--actually 11.6 billion bits, or gigabits, per square inch, every square inch of disk space could hold 1,450 average-sized novels or more than 725,000 pages of double-spaced typewriter pages, which would make a stack taller than an 18-story building. "With this laboratory demonstration, we're on track to providing products with 10-gigabit density by the year 2001," says Robert Scranton, IBM Storage Systems Div. vice president for technology. Since 1991, when IBM introduced the industry's first magnetoresistive sensor for reading data on hard disks, data density has increased 60% per year. Over the past six years the average data-storage capacity of disk drives sold worldwide has increased 18-fold, while the price per megabyte has dropped 52-fold, says DiskTrend.