RTC Magazine

Flash memory’s drastically dropping price in conjunction with its inherent non-volatility makes it a prime candidate for mass storage integration, although its write performance and endurance make such an implementation difficult. RAM on the other hand is extremely fast in both reads and writes, but its cost per capacity has slowed its enterprise adoption. These two storage technologies are now being merged together to create Cached Flash systems that leverage the capacity, price and non-volatility of flash with RAM’s unmatched speed and performance.

Solid-state disk, commonly referred to as SSD, uses a volatile (RAM) or non-volatile (flash) memory as the primary storage media. If the systems are built using RAM, there will always be battery backup to internal hard disk drives to preserve data even if external power is lost. From the point of view of the operating system, SSD systems attach and behave just like hard disk drives. It is important to maintain the distinction between RAM and flash memory, although both are “solid state” in nature, their capabilities and composition are far from similar.

Flash memory has been getting a lot of exposure and is a very appealing technology due to its inherent non-volatility, ruggedness, low power consumption and rapidly dropping price. This technology has been around since the late 1980s but was first brought to market in the early 1990s by Toshiba. Many of these factors make it a prime candidate to be a successful technology in the consumer market since it can be integrated into many existing technologies as an alternative for hard disk.

There are downsides to flash memory: its writes are extremely slow, coming in slower than hard disks in some cases, and it has limited write endurance, meaning that the chips will render themselves unusable in a matter of 10,000 to 100,000 writes depending on the type of flash chip used. Multi-layer chip (MLC) technology is specified to perform 10,000 writes before wearing out while single-layer chip (SLC) technology is rated at up to 100,000 writes.

Random Access Memory, or RAM, is a more mature technology than flash and can process both reads and writes at 10-15 nanoseconds, although it is inherently volatile and therefore requires a power source in order for it to operate and retain information on the chip. RAM has made quite a footprint in the mass storage arena as well, given its equal write and read performance and its capability of executing a seemingly unlimited number of transactions. An overview of the usefulness of different storage technologies for various data patterns is given in Table 1.

Consumer Applications

Flash is very attractive to the consumer market. Overall, the most appealing aspects of this technology are its ruggedness, density, low power consumption, price per solution and performance respectively. The most prevalent applications for flash are cameras, portable media and thumb drives. Recently both portable media devices and laptops have started integrating this non-volatile technology as well, but more for the purpose of hard disk replacement.

Thumb drives—also known as pen drives, USB drives and flash drives—are essentially small, portable, flash memory devices that connect to computers via a USB drive and can store information without a power source as well as quickly and easily enable sharing of information between computers. Ruggedness is the most important feature of this technology since it needs to survive everyday wear-and-tear activities such as being dropped or accidentally being put through the washing machine and still maintain its data integrity.

Density is important for this technology as well since, although this device is small, it is rather inconvenient to have to carry more than one around at a time, and if large file transfers are necessary, at least one gigabyte of data will be required to hold the desired amount of data. Low power is also essential, and although the amount of power needed to perform a transfer is not as important, the fact that the device can retain all the information with no power at all makes for a purely portable memory device. As flash densities improve, expect an ever growing list of applications for the USB thumb drive. It is not far-fetched to believe that most software and possibly movies could be distributed on this technology in the next five years.