Memory Standards

Older portables often used proprietary memory modules, meaning that they were custom designed by the system manufacturer and normally could be purchased only from that manufacturer. That meant not only that replacing or upgrading memory was expensive, but that memory was also harder to find, because in many cases the memory could be purchased only from the original manufacturer. Some of the first laptop systems in late '80s and early '90s used proprietary memory cartridges that looked like modern PC Cards but plugged into a dedicated Personal Computer Memory Card International Association (PCMCIA) memory socket inside the system. Gradually, most of the manufacturers shifted their designs to using industry-standard memory modules, which are interchangeable, much easier to find, and much less expensive overall. Most modern systems now use industry-standard memory modules that are specifically designed for smaller or portable systems. Most of these industry-standard memory chip and module designs are created by the Joint Electron Devices Engineering Council (JEDEC) Solid State Technology Association.

JEDEC

JEDEC (Joint Electron Devices Engineering Council) is the semiconductor engineering standardization body of the Electronic Industries Alliance (EIA), a trade association that represents all areas of the electronics industry. JEDEC, which was originally created in 1960, governs the standardization of all types of semiconductor devices, integrated circuits, and modules. JEDEC has about 300 member companies, including memory, chipset, and processor manufacturers as well as practically any company involved in manufacturing computer equipment using industry-standard components.

The idea behind JEDEC is simple: If one company were to create a proprietary memory technology, for example, then other companies that wanted to manufacture components compliant with that memory would have to pay license fees, assuming the company that owned it was interested in licensing at all! Parts would be more proprietary in nature, causing problems with interchangeability or sourcing reasonably priced replacements. In addition, those companies licensing the technology would have no control over future changes made by the owner company.

JEDEC helps to prevent that type of scenario for items such as memory, by getting all the memory manufacturers to work together creating shared industry standards covering memory chips and modules. JEDEC-approved standards for memory could then be freely shared by all the member companies, and no one single company would have control over a given standard, or any of the companies producing compliant components. FPM, SDRAM, DDR SDRAM, and DDR2 SDRAM are examples of JEDEC memory standards used in PCs, whereas EDO and RDRAM are proprietary examples. You can find out more about JEDEC standards for memory and other semiconductor technology at www.jedec.org.

Although there are various industry-standard types of memory and modules, most modern portables including laptops, notebooks, and Tablet PCs use one of several types of DIMMs called small outline dual inline memory modules (SODIMMs). SODIMMs are physically smaller but similar electrically to the larger DIMMs used in desktop systems. SODIMMs typically are available in extended data out (EDO) or synchronous dynamic RAM (SDRAM) form, with various speeds and voltages available. An even smaller class of modules, called micro dual inline memory modules or MicroDIMMs, are used by subnotebook, palmtop, and handheld systems. They are available in several industry-standard JEDEC-approved designs as well.

In any case, be sure the memory you purchase works with your system or that you can get a refund or replacement if it doesn't. Even though industry standards exist and modules from many sources will often fit a given system, I normally recommend that you look for memory modules that the system manufacturer has approved for the system, in the configurations the manufacturer specified. Often you can find a list of approved modules or suppliers in the system documentation or on the system manufacturer's website.