Number of memory modules

A memory module or memory latch is a small circuit board on which several memory components (dynamic RAM in the form of integrated circuits) are soldered. Memory modules form or expand the main memory of electronic devices such as computers or printers and are plugged into specially designed slots.

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Memory type

DDR-SDRAM ("Double Data Rate Synchronous Dynamic Random Access Memory") is a type of random access memory (RAM) currently available in three categories. DDR-SDRAM with 184 contacts, DDR2-SDRAM with 240 contacts and DDR3-SDRAM also with 240 contacts. They are mainly used for memory modules of the DIMM or SO-DIMM standard as main memory in PCs and laptops.

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Memory chip

Random-access memory is a form of computer data storage. A random-access device allows stored data to be accessed directly in any random order. In contrast, other data storage media such as hard disks, CDs, DVDs and magnetic tape, as well as early primary memory types such as drum memory, read and write data only in a predetermined order, consecutively, because of mechanical design limitations. Therefore the time to access a given data location varies significantly depending on its physical location.

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Memory form factor

A DIMM or dual in-line memory module, comprises a series of dynamic random access memory integrated circuits. These modules are mounted on a printed circuit board and designed for use in personal computers, workstations and servers. DIMMs began to replace SIMMs (single in-line memory modules) as the predominant type of memory module as Intel P5-based Pentium processors began to gain market share.

The main difference between SIMMs and DIMMs is that DIMMs have separate electrical contacts on each side of the module, while the contacts on SIMMs on both sides are redundant. Another difference is that standard SIMMs have a 32-bit data path, while standard DIMMs have a 64-bit data path.

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RAM buffer

In addition to bandwidth and capacity variants, modules can
1. Optionally implement ECC, which is an extra data byte lane used for correcting minor errors and detecting major errors for better reliability. Modules with ECC are identified by an additional ECC in their designation.
2. Be "registered", which improves signal integrity (and hence potentially clock speed and physical slot capacity) by electrically buffering the signals at a cost of an extra clock of increased latency. Those modules are identified by an additional R in their designation, whereas non-registered (a.k.a. "unbuffered") RAM may be identified by an additional U in the designation.
3. Be Fully buffered modules, which are designated by F or FB and do not have the same notch position as other classes. Fully buffered modules cannot be used with motherboards that are made for registered modules, and the different notch position physically prevents their insertion.

CAS latency

CAS latency is the delay time which elapses between the moment a memory controller tells the memory module to access a particular column in a selected row, and the moment the data from the given array location is available on the module's output pins.

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tRCD

The parameter tRCD (RAS-to-CAS delay, row-to-column delay) describes for a DRAM the time that must have elapsed after activation of a word line (activate) before a read command may be sent.

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tRAS

The parameter tRAS (RAS pulse width, Active Command Period, Bank Active Time) describes the time that must have elapsed after a line (or a line in a bank) has been activated before a command to deactivate the line (precharge, closing the bank) can be sent.

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tRP

The parameter "tRP" ("Row Precharge Time") describes the minimum time that must have elapsed after a precharge command before a new command may be sent to activate a line in the same bank.

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Voltage

The voltage between two points is a short name for the electrical force that would drive an electric current between those points. Specifically, voltage is equal to energy per unit charge. In the case of static electric fields, the voltage between two points is equal to the electrical potential difference between those points. In the more general case with electric and magnetic fields that vary with time, the terms are no longer synonymous.

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