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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 Ram, ram, or RAM may refer to: Animals * A male sheep * Ram cichlid, a freshwater tropical fish People * Ram (given name) * Ram (surname) * Ram (director) (Ramsubramaniam), an Indian Tamil film director * RAM (musician) (born 1974), Dutch * Raj ...
to
DDR4 SDRAM Double Data Rate 4 Synchronous Dynamic Random-Access Memory (DDR4 SDRAM) is a type of synchronous dynamic random-access memory with a high Bandwidth (computing), bandwidth ("double data rate") interface. Released to the market in 2014, it is a v ...
modules.


JEDEC standardization goals

The Joint Electron Device Engineering Council characterizes its standardization efforts as follows:


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.


Units of information

The specification defines the two common units of information: * The
bit The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represented ...
(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 uni ...
(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 definitions of the commonly used prefixes
kilo KILO (94.3 FM, 94.3 KILO) is a radio station broadcasting in Colorado Springs and Pueblo, Colorado. It also streams online. History KLST and KPIK-FM The 94.3 signal signed on the air on August 22, 1962, as KLST, owned by Little London Broa ...
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mega Mega or MEGA may refer to: Science * mega-, a metric prefix denoting 106 * Mega (number), a certain very large integer in Steinhaus–Moser notation * "mega-" a prefix meaning "large" that is used in taxonomy * Gravity assist, for ''Moon-Eart ...
, and
giga Giga ( or ) is a unit prefix in the metric system denoting a factor of a short-scale billion or long-scale milliard (109 or ). It has the symbol G. ''Giga'' is derived from the Greek word (''gĂ­gas''), meaning "giant". The '' Oxford English D ...
"as a prefix to units of semiconductor storage capacity" to designate multiples of the units. The specification cites three prefixes as follows: * ''kilo'' (''K''): A multiplier equal to 1024 (210). * ''mega'' (''M''): A multiplier equal to (220 or K2, where K = 1024). * ''giga'' (''G''): A multiplier equal to (230 or K3, where K = 1024). The specification notes that these prefixes are included in the document only to reflect common usage. It refers to the IEEE/ASTM SI 10-1997 standard as stating that "''this practice frequently leads to confusion and is deprecated''". The JEDEC specification takes no explicit position on this usage. The document further refers to the description of the IEC
binary prefixes A binary prefix is a unit prefix for multiples of units. It is most often used in data processing, data transmission, and digital information, principally in association with the bit and the byte, to indicate multiplication by a power of ...
in Amendment 2 of IEC 60027-2, ''"Letter symbols to be used in electrical technology"'', for an alternate system of prefixesQuote from JEDEC Standard 100B.01, page 8: and includes a table of the IEC prefixes in the note. However the JEDEC specification does not explicitly include the IEC prefixes in the list of general terms and definitions. The document notes that these prefixes are used in their decimal sense for
serial communication In telecommunication and data transmission, serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. This is in contrast to parallel communication, where several bits are s ...
data rates measured in
bit The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represented ...
s.


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:
1GB 2Rx4 PC2-3200P-333-11-D2 is a 1 GB DDR2 Registered DIMM, with address/command parity function, using 2 ranks of x4 SDRAMs operational to PC2-3200 performance with
CAS Latency Column Address Strobe (CAS) latency, or CL, is the delay in clock cycles between the READ command and the moment data is available. In asynchronous DRAM, the interval is specified in nanoseconds (absolute time). In synchronous DRAM, the interval ...
= 3, tRCD = 3, tRP = 3, using JEDEC SPD revision 1.1, raw card reference design file D revision 2 used for the assembly.


Storage capacities

The JEDEC terms dictionary includes definitions for prefixes 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.''"


See also

*
IEC 60027 IEC 60027 (formerly IEC 27) is a technical international standard for letter symbols published by the International Electrotechnical Commission (IEC), comprising the following parts: * IEC 60027-1: General * IEC 60027-2: Telecommunications and ele ...
*
ISO/IEC 80000 ISO 80000 or IEC 80000 is an international standard introducing the International System of Quantities (ISQ). It was developed and promulgated jointly by the International Organization for Standardization (ISO) and the International Electrotech ...
*
Timeline of binary prefixes This timeline of binary prefixes lists events in the history of the evolution, development, and use of units of measure for information, the bit and the byte, which are germane to the definition of the binary prefixes by the International Electr ...


Notes


References

{{reflist, 30em


External links


Online JEDEC documents

JESD218
Units of information JEDEC standards