In a spin

For some time, flash memory has been the ‘go to’ technology for a range of applications, particularly those where a lot of non volatile storage is needed. Available in two ‘flavours’ – NOR and NAND – the technology offers fast read and write times, as well as high levels of shock resistance. It is for these reasons that flash is finding widespread application in devices such as mobile phones, PDAs and MP3 players – not only in industry standard packages, but also in the various memory card formats. NOR flash brings more versatility, supporting random access to any memory location, but at the expense of read and write speeds. NAND, by contrast, offers faster reads and writes, but only allows access to blocks of memory. So NAND is the preferred solution for hard disk replacement, while NOR is a more obvious program rom replacement. As process technology has scaled, flash memories have got larger. But the leading flash developers have increased flash capacity beyond that through multi level cells. Where previously the devices could only store 1bit per cell – the 1s and 0s of digital data – today’s parts support four levels, representing 2bits of data. But process shrinks are creating a physical limit to just how far flash technology can be taken before it can’t be made any smaller. Some projections point to flash reaching the ‘wall’ at the 22nm node. Whilst further work on multi level cell technology may increase flash’s storage capacity, the industry has been looking for other approaches that might take over – not only from flash, but also from the other memory technologies in use – to create what’s been termed a ‘universal memory’.