计算机专业时文选读(984)

Future Memories

Chip makers are searching for cheap, fast, “universal” memories to replace DRAM, SRAM and flash.

For 40 years, systems designers have seen memory densities double every 18 to 24 months while memory chip prices have remained essentially flat, cutting the cost per bit in half each time. As the technical challenges of building ever-smaller memory cells in silicon have increased, however, some memory manufacturers have predicted that the cost curve will start to swing the other way before the end of the decade.

Researchers are working on several alternate technologies that could eventually replace those in the three memory types commonly used today: low-cost dynamic RAM (DRAM), used in PCs and servers; fast static RAM (SRAM), used for processor caches and mobile devices; and nonvolatile flash memory, used in everything from computer BIOSs to cell phones.

Researchers at IBM, Intel Corp. and other companies envision the development of a universal memory technology that could someday replace all three.

A universal memory technology could change how computers are designed. For example, nonvolatile RAM could allow computers to boot up and power down instantly because stored information wouldn’t be lost when power was. But the emergence of a universal memory technology is probably at least 10 to 15 years away.

Others argue that a universal memory isn’t possible because one memory type can’t satisfy all needs. For example, nothing could be the fastest and cheapest at the same time.

Most research today is focused on addressing the limitations of one memory technology at a time, such as flash. But some attributes of today’s technologies will be hard to beat.

Most technologies will probably not be able to compete on lowest cost per bit against DRAM or with the fastest SRAM. So they will fall into that space in between. Ferroelectric RAM (FRAM) and magnetoresistive RAM (MRAM) are the best-funded and most-evolved of the emerging memory technologies. FRAM is a nonvolatile RAM that was developed by Ramtron International Corp. in Colorado Springs. It’s licensed by Texas Instruments Inc. and others. More than 30 million products have already shipped using FRAM, including metering, radio frequency identification and smart-card devices.

FRAM, which is based on nanoscale “quantum dots,” uses less power and writes faster than DRAM or flash, and it has a long life span. But the technology remains 20 to 50 times more expensive per bit than DRAM, and chip density is far lower. Ramtron is prototyping 1Mbit parts today and hopes to push the technology to 4Mbit or 8Mbit in 2006. Until MRAM is ready for the market, however, FRAM is the only game in town for nonvolatile DRAM. (To Be Continued)

未来的存储器(1)

芯片制造商正在寻找廉价、快速、通用的存储器来替代DRAM、SRAM和闪存。

四十年来，系统设计师看到了每18至24个月存储器密度翻一番，而存储器芯片的价格基本保持不变，每次每比特的成本会降低一半。然而，随着在硅片上制造越来越小存储单元的技术挑战增加，有些存储器制造商预测，到本十年末成本曲线将向另外一个方向摆动(即成本增大)。

研究人员正在研究几种替代技术，最终替代今天常用的三类存储器：低成本的用于PC机和服务器的动态RAM(DRAM)、用作处理器高速缓存和用于移动设备中的快速静态RAM(SRAM)、以及用于从计算机BIOS到手机电话等各种设备中的非易失性闪存。

IBM、Intel和其他公司的研究人员设想开发一种通用的存储器技术，有一天能把这三类存储器统统替代掉。

通用的存储器技术有可能改变计算机的设计。例如，非易失性RAM能让计算机立即启动和关机，因为存储的信息不会在断电时丢失。但通用存储器技术的出现可能至少还有十年之遥。

其他一些人则称通用存储器是不可能的，因为一种存储器不可能满足所有的需求。例如，没有一样东西可以是最快同时又是最便宜的。

今天大多数的研究集中在一次解决一种存储器技术(如闪存)的局限。但今天技术的有些属性是很难克服的。

多数技术大概不可能在每位最低成本上与DRAM竞争，而在速度与最快的SRAM竞争。因此它们将处于这两者之间的空间。铁电RAM(FRAM)和磁阻RAM(MRAM)是存储器新技术中投入最多、研究最深入的两项技术。FRAM是非易失性RAM，它是由Ramtron国际公司开发的。德州仪器等公司已获得了(该技术的)许可。已经有3000多万台使用FRAM的设备交付使用，包括测量仪器、RFID和智能卡设备等。

基于纳米级“量子点”的FRAM比起DRAM和闪存耗电更低、写更快、有更长的生命周期，但这项技术的位成本要比DRAM贵20～50倍，而芯片的集成度低得多。现在，Ramtron公司正在试生产1兆位的零件，希望在2006年将此技术提升到4兆位或8兆位。在MRAM能上市之前，FRAM将是市场上惟一的非易失性DRAM。(未完待续)