Memory grade is a construction protocol for DRAM chips, consisting of a 64-bit bus and an 8-bit chip. A memory rank is an array of connected DRAM chips, with ranks ranging from single to octal. JEDEC established the 64-bit bus and 8-bit ECC chip standard. The more layers a rank has, the more memory it can store. Most consumer computers only have single or double layer memory, while servers use quad or octal layer rated memory chips.
Memory grade is a type of construction applied to DRAM (Dynamic Random Access Memory) chips. As a protocol, all ranks must consist of a 64-bit bus and an 8-bit chip, equaling a total width of 72 bits. Although the memory rank must be 64 bits wide, the rank can consist of chips of different sizes. Ranks can be single, double, quadruple, or octal, although most consumer computers only see single and double. Higher ranks, which contain more memory, are typically seen on high-end computers and servers.
A memory rank is the array of several connected DRAM chips. DRAM is different from regular random access memory (RAM) in that each piece of information is stored in a different capacitor on the chip. This allows DRAM to recall information better than RAM. By creating a memory rank system, DRAM is able to store more memory overall while still being compact and inexpensive.
The JEDEC Solid State Technology Association (JEDEC), formerly known as the Joint Electron Devices Engineering Council, is an independent council that decides on various protocols and standards for computer architecture and construction. The organization decided that the most efficient way to build a memory rank would be to use a 64-bit bus, which refers to chip size, along with an 8-bit Error Correction Code (ECC) chip for a combined width of 72 bits. To meet these standards, the rank cannot be greater or less than this width.
While the memory rank width is standard, the size of the chips need not be. For example, one company might create a rank with a single 64-bit chip, but another company might create a rank of eight 8-bit chips, and another might create a rank of 16-chip 4-bit and all three would be considered a standard memory grade. As long as the total is 64 bits, excluding the ECC, it fits the standard. There may also be several chips per layer; one piece of DRAM may have one 4-bit 16-bit layer, while another layer consists of eight 8-bit chips. Most companies prefer to use more chips, because this gives DRAM more processing power and more areas to store data.
As of 2011, there are four types of rank: single or one layer, double or two layer, quad or four layer, and octal or eight layer. The more layers, the more memory the company can fit on a chip. Commonly, consumers only find single or dual layer memory in their computers, while powerful server computers make use of quad and octal layer rated memory chips.
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