Hardware Reference
In-Depth Information
For memory to be as inexpensive and interchangeable as possible, industry-standard specifications
for both chips and modules have been developed. The Joint Electron Device Engineering Council
(JEDEC) Solid State Technology Association creates most industry-standard memory chip and
module designs.
JEDEC
JEDEC 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 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 and 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 the owner
company made.
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, DDR2,
DDR3, and DDR4 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
.
Because of variations on speeds (timing), voltage, and other issues, purchasing memory matching the
correct industry-standard type doesn't guarantee that it will work in a given system. Always 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 do exist, allowing modules from many sources to fit a given
system, I normally recommend that you look for memory modules that the system or memory
manufacturer has approved for the system. Often you can find a list of approved modules or suppliers
in the system documentation or on the system or memory module manufacturer's website.
Speed and Performance
The speed and performance issues with memory are confusing to some people because of all the
different ways to express the speeds of memory and processors. Memory speed was originally
expressed in nanoseconds (ns), whereas the speeds of newer forms of memory are usually expressed
in megahertz (MHz) and megabytes per second (MBps) instead. Processor speed was originally
expressed in megahertz (MHz), whereas most current processor speeds are expressed in gigahertz
(GHz). Although all these different speed units might seem confusing, it is relatively simple to
