The JEDEC memory standards are the specifications for semiconductor memory circuits and similar storage devices promulgated by the JEDEC

JEDEC

The JEDEC Solid State Technology Association, formerly known as the Joint Electron Devices Engineering Council , is an independent semiconductor engineering trade organization and standardization body...

 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 the latest DDR3 SDRAM

DDR3 SDRAM

In computing, DDR3 SDRAM, an abbreviation for double data rate type three synchronous dynamic random access memory, is a modern kind of dynamic random access memory with a high bandwidth interface. It is one of several variants of DRAM and associated interface techniques used since the early 1970s...

 modules. In August of 2011, JEDEC announced that its DDR4 standard is expected to be published in mid-2012.

JEDEC standardization goals

JEDEC characterizes its standardization efforts as follows:

JEDEC Standard 100B.01

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 storage

The specification defines the two common units of information storage:

• bit (b): In the binary numeration system, either of the digits 0 or 1. (Ref. ANSI X3.172.)
• byte (B): A binary character string operated upon as a unit and usually shorter than a computer word. (Ref. ANSI X3.172.) NOTE: A byte is usually eight bits.

Unit prefixes for semiconductor storage capacity

The specification contains definitions of the commonly used prefixes kilo, mega, giga, and tera usually combined with the units byte

Byte

The byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...

 and bit

Bit

A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...

 to
designate multiples of the units.

The specification defines these prefixes as follows:

• kilo (K): A multiplier equal to (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).
• tera (T): A multiplier equal to (2⁴⁰ or K⁴, 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". However the JEDEC specification does not explicitly deprecate the common usage. The document further refers the reader to the description of the IEC binary prefixes 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

Serial communication

In telecommunication and computer science, 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 sent as a whole, on a link with several parallel channels...

 data rates measured in bit

Bit

A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...

s.

All JEDEC standards avoid the use of the terms megabit, megabyte, gigabyte, terabyte, etc, and refer to memory capacity as a number followed by the units. (64Mb, 256MB, 1GB, or 4TB.)

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. Additions to Standard 21 are so frequent that it is published in loose-leaf format and comes in a three-ring binder.
In the 1980s the configuration of a family of memories could be specified on a single page. Modern memory modules require over 100 pages; standards for the memory IC and a reference design of the module. The standards specify the physical dimensions for the module, the electrical characteristics for the module and even the data for doing computer simulations of the memory module operating in a system.

A memory module like the DDR2-SDRAM is available for laptop, desktop, and server computers. There is also a wide selection of memory capacities and 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

CAS Latency

Column Address Strobe latency, or CL, is the delay time between the moment a memory controller tells the memory module to access a particular memory column on a RAM memory module, and the moment the data from given array location is available on the module's output pins...

= 3, tRCD = 3, tRP = 3, using JEDEC SPD revision 1.1, raw card reference design file D revision 2 used for the assembly.