Parity memory

Memory modules have traditionally been available in two basic flavours: non-parity and parity. Parity checking uses a ninth memory chip to hold checksum data on the contents of the other eight chips in that memory bank. If the predicted value of the checksum matches the actual value, then all is well. If it does not, then the contents of memory is corrupted and unreliable. In this event a non-maskable interrupt (NMI) is generated to instruct the system to shut down and thereby avoid any potential data corruption.

Parity checking is quite limited - only odd numbers of bit errors are detected (two parity errors in the same byte will cancel themselves out) and there's no way of identifying the offending bits or fixing them - and in recent years the more sophisticated and more costly Error Check Code (ECC) memory has gained in popularity.

Flash memory

Flash memory is a solid-state, non-volatile, rewritable memory that works like RAM and a hard-disk drive combined. It resembles conventional memory, coming in the form of discrete chips, modules, or memory cards. Just like with DRAM and SRAM, bits of electronic data are stored in memory cells, and just like with a hard disk drive, flash memory is non-volatile, retaining its data even when the power is turned off.

Notwithstanding its apparent advantages over both RAM (its non-volatility) and hard disk (the absence of moving parts), there are a number of reasons why flash memory is not a viable replacement for either. Because of its design, flash memory must be erased in blocks of data rather than single bytes like RAM. This, together with its significantly higher cost and the fact that memory cells in a flash chip have a limited lifespan of around 100,000 write cycles, make it an inappropriate alternative to RAM for use as a PC's main memory. Whilst electronic "flash drives" are smaller, faster, consume less energy and are capable of withstanding shocks up to 2000 Gs - equivalent to a 10 foot drop onto concrete - without losing data, their limited capacity (around 100MB) make them an inappropriate alternative to a PC's hard disk drive. Even if capacity were not a problem, as with RAM, flash memory cannot compete with hard disks in price.

Since its inception in the mid-1980s, flash memory has evolved into a versatile and practical storage solution. Several different implementation exist. NOR flash is a random access device appropriate for code storage applications. NAND flash - optimised for mass storage applications - is the most common form. Its high speed, durability, and low voltage requirements, have made it ideal for use in many applications - such as digital cameras, cell phones, printers, handheld computers, pagers, and audio recorders.

Samsung Electronics is the leading flash memory producer, and indeed, the leading producer of memory products in general. Its SmartMedia flash memory cards first appeared in 1996 and - along with CompactFlash - have gone on to become one of predominant flash memory formats. In late 1999 the company announced the world's first 1GB flash memory prototype, based on 0.15 micron process technology. The following year its largest capacity card to date - at 128MB - came to market, with a 512MB chip slated for mass production in 2001.

However, at the very time capacities were growing apace, flash memory found itself facing a challenge from a radical new memory chip technology, in the shape of Magnetic RAM. 3380