Is solid state memory better than magnetic memory?

Moore’s Law, or more specifically, Gordon Moore, predicted in 1965 that transistor density in chips would double about every two years. For the past 50 years, this observation has held true and is the fundamental driving force behind most advances in technology leading to computers becoming smaller, faster, cheaper and more reliable. Typically, Moore’s Law has resulted in solid-state memory becoming smaller and cheaper. However, the ever-increasing need for greater storage capacity has had manufacturers sacrificing reliability and performance in some cases. Apparently, the solid-state memory area presents a major dichotomy.

The solid-state memory arena has seen exponential growth in the past 15 years. Many have not even seen a floppy disk as it was replaced almost overnight by the thumb drives. These solid-state drives also made ZIP drives disappear shortly thereafter. With the increase in digital storage in smartphones, CD players and CD drives became obsolete.

There is no doubt that solid state media is superior to the mechanical, rotating magnetic memory media, which we commonly known as the Hard Disk Drive, in most applications. However, surprising as it may seem, the solid-state media has some characteristics that do not allow it to follow Moore’ Law, making it less than optimal for some types of applications.

For example, flash memory is known to have a limited life, as it wears out over time. With the technological improvements we have been witnessing year-over-year, one would assume that flash endurance has gradually improved; however, reality says otherwise. In the ancient days (read 8 years ago), SLC NAND memory was rated to give 100,000 write/erase cycles. Currently manufactured SLC NAND memory has a life of 50,000 write/erase cycles. In the case of MLC NAND memory, the reduction is even more dramatic. Older MLC NAND memories had a life of about 10,000 write/erase cycles, current MLC NAND memories are limited to 3,000 write/erase cycles.

That means newer flash memories wear out more quickly, and in addition, do not perform as well. This can be attributed in part to the stronger EDC or Error Detection and Correction requirements for newer flash. This is evident from the decreasing write/erase cycles and the increasing ECC or Error Correcting Code requirements following a reduction in the NAND flash lithography.

This reduced lifespan may not be so much of a problem for many consumer devices. For example, MLC NAND memory within a cell phone is likely to outlast the mobile phone itself; assuming an original owner lifespan of two years.

Industrial devices using solid-state media would face a different story. Typically, devices manufactured for industrial use have an expected lifetime of 10, 15 or more years. That makes endurance of solid-state media in such devices very critical.

Although flash lifespan is measured in cycles of write/erase, interestingly, only the erase operation counts against the life of flash memory. That means, you could use up the flash simply by erasing it repeatedly, while not writing anything to it at all. It does not matter whether you write a small or a large amount of data; what matters is how many times you erased it.