Flash Drives: application

Flash Drive Technology

The terms “hard drive” or “drive” are often used to simply designate an abstract storage device. Two examples of this trend are the solid state hard drive and the flash drive. The solid state hard drive is not really a “hard drive” in the original meaning of the word because it has no moving parts and the data is not stored on magnetic platter. It is merely called a hard drive because the term has become synonymous for general purpose storage devices. Many solid state hard drives have external form factors which allow it to be used in place of the traditional hard disk drive. Though a solid state drive costs more per gigabyte, it has many advantages over the original hard drive. Another name for the solid state hard drive is the solid state disk (SSD). No matter what the name, the key distinction is that the SSD stores its data in a semiconductor material such as NAND flash or SDRAM.


Not having any moving parts, means that the solid state drive has fewer reasons to break. This translates into increased reliability. By not being a mechanical device, it has advantages such as low power consumption, survivability in hostile environments and quicker access times. An SSD can use either non-volatile memory such as flash, or volatile memory such as SDRAM. When volatile RAM is used, the vendor puts the disk into a rack mountable case with a battery to preserve power in the event of an unexpected power outage. These silicon based disks are mostly used in military, corporate computer room, and industrial environments. Access times for the solid state hard drive can be up to 500 times faster than for the hard disk. In contrast, the hard disk is much slower because it has to go through the motions of moving the heads and waiting for the platters to rotate to the desired position before data can even be read. Improving disk access times is very beneficial when an application uses lots of small files. Some environments are too hostile for a drive with a spinning platter to survive for long. The mechanical drive is too susceptible to damage from moisture, dust, vibrations, shock, and extreme temperatures. In sharp contrast, the solid state hard drive will survive more easily in all of these environments.


But the solid state drive is not immune to problems, foremost of which is that flash memory has a limited number of read/write cycles. Another problem for NAND flash has to do with the large block sizes. The block sizes of NAND flash disks can easily be 64KB or larger. The issue, for writes, is that the entire block needs to be written, even if only one byte has to change. It gets even worse because the entire block needs to be erased before the new data can be written. Understandably, this creates huge performance pot holes when large numbers of tiny files are being updated. Because of this, NAND flash works best when large blocks of sequential writes make up the bulk of the I/O load. Hybrid Drive The hybrid drive is a hard disk that incorporates some of the benefits of the solid state drive. The hybrid drive has a large amount of flash memory incorporated into the hard disc electronics. The flash is used as a cache to speed up disk access. Windows Vista provides a feature called ReadyDrive which is designed to take advantage of the hybrid drive. ReadyDrive will help the PC to boot faster and reduce power consumption. The continued decline in prices of flash and SDRAM will make solid state hard drives more attractive to the consumer market. They are already being used in some high-end portable computers. The Flash drive is a portable solid state disk. The term Flash is used to describe non-volatile solid-state memory that can be rewritten many times. Other devices such as the solid state drive can use Flash memory, but this term more commonly refers to the car key sized USB Flash drive. Other names for this portable drive are: thumb drive, pen drive, jump drive, and memory stick. Some of these names are marketing names but they all convey the idea that this is a compact, lightweight, and portable drive. It’s as easy to carry as your car key. The memory stick is rapidly replacing the floppy for many reasons. This compact and lightweight drive is more durable than a floppy. Flash memory can hold data for up to 10 years. And it has also been known to survive immersion in water. However, if your flash drive does get wet, it is vital to wait for it to completely dry before plugging it into the USB port. Many motherboards can support booting from a USB drive. If your main hard drive fails to boot for some reason, it can be helpful to have a bootable pen drive available. This recovery drive could have a disk repair utility or you could just use it to see if the hard drive is still readable. Best of all, prices are constantly falling, and sizes are constantly increasing. We are truly getting more for less. I hesitate to even mention what the largest size of a thumb drive is today because it will be out of date tomorrow. These memory sticks are so versatile and inexpensive; you can hardly go wrong by always having one available. There are two types of flash memory: NAND flash and NOR flash. NOR flash is like SDRAM were each individual byte can be accessed directly, and NAND flash is more like a block access device (think hard drive) where the data is read and written in large blocks at a time. NOR is typically used for firmware and NAND is used for flash drives of all sorts. Flash drives are starting to replace hard drives in some specialized applications such as mobile devices and rugged portable computers. However, NAND flash still has some enormous problems to overcome before it can completely replace the magnetic rotating platters we have come to know as the hard disk drive. The most obvious hurdle is the cost per GB but this is a small hurdle for a disruptive technology that has so many benefits, foremost of which are its resistance to vibration and faster access times. The bigger hurdle has to do with the larger block sizes and the shorter read/write lifetime of NAND flash memory. Because of this, were not likely to see the hard drive go away anytime soon.