The JEDEC memory standards are the specifications for semiconductor memory circuits and similar storage devices promulgated by the
Joint Electron Device Engineering Council (JEDEC) Solid State Technology Association, a semiconductor trade and engineering standardization organization.
JEDEC Standard 100B.01 specifies common terms, units, and other definitions in use in the semiconductor industry. JESC21-C specifies semiconductor memories from the 256 bit static
RAM to
DDR4 SDRAM modules.
JEDEC standardization goals
The Joint Electron Device Engineering Council characterizes its standardization efforts as follows:
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JEDEC Standard 100B.01
The December 2002 JEDEC Standard 100B.01 is entitled ''Terms, Definitions, and Letter Symbols for Microcomputers, Microprocessors, and Memory Integrated Circuits''. The purpose of the standard is to promote the uniform use of symbols, abbreviations, terms, and definitions throughout the semiconductor industry.
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Units of information
The specification defines the two common units of information:
* The bit (b) is the smallest unit of information in the binary numeration system and is represented by the digits 0 and 1.
* The byte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable un ...
(B) is a binary character string typically operated upon as one unit. It is usually shorter than a computer word.
Unit prefixes for semiconductor storage capacity
The specification contains citations of the commonly used prefixes kilo, mega, and giga
Giga- ( or ) is a metric prefix, unit prefix in the metric system denoting a factor of a Long and short scales, short-scale billion or long-scale milliard (109 or 1,000,000,000). It has the symbol G.
''Giga-'' is derived from the Ancient Greek, ...
to prefix units of semiconductor storage capacity.
The specification cites three prefixes as follows, with the note that these prefixes are included in the document only to reflect common usage.
* ''kilo (K) (as a prefix to units of semiconductor storage capacity)'': A multiplier equal to 1024 (210).
* ''mega (M) (as a prefix to units of semiconductor storage capacity)'': A multiplier equal to (220 or K2, where K = 1024).
* ''giga (G) (as a prefix to units of semiconductor storage capacity)'': A multiplier equal to (230 or K3, where K = 1024).
It refers to the IEEE/ASTM SI 10-1997 standard as stating that "''this practice frequently leads to confusion and is deprecated''". The document further refers to the description of the IEC binary prefixes
A binary prefix is a unit prefix that indicates a multiple of a unit of measurement by an integer power of two. The most commonly used binary prefixes are kibi (symbol Ki, meaning ), mebi (), and gibi (). They are most often used in inform ...
in Amendment 2 of IEC 60027-2, "''Letter symbols to be used in electrical technology''", for an alternate system of prefixes[Quote from JEDEC Standard 100B.01, page 8:] and includes a table of the IEC prefixes in the note.
The document notes that these prefixes are used in their decimal sense for serial communication data rates measured in bits.
The JEDEC terms dictionary further includes, under the entry for ''mega'', definitions for the binary prefixes
A binary prefix is a unit prefix that indicates a multiple of a unit of measurement by an integer power of two. The most commonly used binary prefixes are kibi (symbol Ki, meaning ), mebi (), and gibi (). They are most often used in inform ...
kibi (Ki), mebi (Mi), gibi (Gi), and tebi (Ti) as powers of 2, and kilo, mega, giga, and tera as powers of 10. For example,
: 240 tebi Ti tera + binary: (210)4 = tera: (103)4
The JEDEC DDR3 SDRAM standard JESD-79-3f uses Mb and Gb to specify binary memory capacity: "''The purpose of this Standard is to define the minimum set of requirements for JEDEC compliant 512 Mb through 8 Gb for x4, x8, and x16 DDR3 SDRAM devices.''"
JESD21-C
The standard ''JESD21-C: Configurations for Solid State Memories'' is maintained by JEDEC committee JC41. This committee consists of members from manufacturers of microprocessors, memory ICs, memory modules, and other components, as well as component integrators, such as video card and personal computer makers. Standard 21 is published in loose-leaf binder format to accommodate frequent updates.
The documentation of modern memory modules, such as the standards for the memory ICs and a reference design of the module requires over one hundred pages. The standards specify the physical and electrical characteristics of the modules, and include the data for computer simulations of the memory module operating in a system.
Memory modules of the DDR2-SDRAM type are available for laptop, desktop, and server computers in a wide selection of capacities and access speeds. The standards specify memory module label formats for end-user markets.[
] For example:
See also
* IEC 60027
* ISO/IEC 80000
* Timeline of binary prefixes
This timeline of binary prefixes lists events in the history of the evolution, development, and use of unit of measurement, units of measure that are germane to the definition of the binary prefixes by the International Electrotechnical Commissio ...
Notes
References
{{reflist, 30em
External links
Online JEDEC documents
JESD218
Units of information
JEDEC standards