Flash memory explored

Flash memory technology is an offspring of the earlier EEPROM (electrically erasable, programmable, read-only memory), which was invented as a convenient means of storing firmware that could be updated without having to remove the chip from the device it controlled.

EEPROM technology supports only occasional write cycles and is relatively slow. Flash, as the name implies, has faster read and write times and allows a much greater number of write cycles.

The main reason for Flash’s speed is that its programming cycles affect whole blocks of memory, rather than individual bytes as in an EEPROM.

Flash was invented in 1984 by Fujio Masuoka at Toshiba. A colleague, Shoji Ariizumi, reportedly suggested the name ‘Flash’ because the burst of high voltage applied during the erasure process reminded him of the flash of a camera.

It’s possible to build Flash memory chips using either a NOR or NAND logic gate configuration. Although the earliest products used NOR gates, designers soon realised that, by sacrificing some flexibility in individually programming and reading memory cells, they could pack a lot more bits into the same area using a NAND gate configuration with serial interconnections. Today, almost all the modules produced are NAND Flash.

Buying products
Buying Flash products can be a confusing and intimidating process. It’s a bit like buying gas and electricity; there are often so many poorly explained options it can be hard to compare products in order to make a purchase decision.

Flash memory products are differentiated by six things; the physical format of the memory (SD card, Memory Stick, Compact Flash and so on), the chip type used for the memory, read and write speeds, added value features such as bundled software or built-in encryption for business use (a fairly recent innovation) and finally the two attributes uppermost in consumers’ minds, storage capacity and price.

Price considerations are often connected with the decision on whether to buy a recognised brand name, a cheaper ‘rebrand’, or a no-name or ‘value’ option. Buying very cheap memory is often a false economy, and its worth very much depends on the value that you place on the data you want to store.

Identifying the type of memory you want, for example USB stick or CF card, is usually self evident, however you do have to be careful when purchasing online, since some vendors’ descriptions can be poorly worded; we’ve explained the pros and cons of the different formats later on. As far as chip type is concerned, for practical purposes, all Flash on the market today is NAND gate based so it’s not something you really need to worry about when you’re shopping.

Making sensible Flash buying decisions is partly about knowing the capabilities of the digital device into which you’re going to be plugging the memory. For example, it may not be worth buying the fastest CF card if the camera you’re going to plug it in to does not support fast (Ultra DMA) memory access. In general, when buying a new super-fast Flash card, to avoid disappointment, it’s well worth checking on the maximum transfer rate supported by your digital devices. Check to make sure they support all the sizes ­ older devices may not work with larger capacity cards, or may need their firmware updated first.