DRAM Marches On

While much has been written here about CPUs and software, fast memory is a key element of computing both personal and on servers. 2012 marks an important evolution of DRAM (Dynamic Random Access Memory). Gone are the days when a few megabytes per second was useful. DDR4 allows 3.2 giga-transfers per second per pin. JEDEC has recently published two relevant standards:

  • MO-309A(PDF, free registration required) entitled, “284 Pin DIMM, 0.85mm pitch”, and
  • JESD79-4(PDF, free registration required), entitled, “DDR4 SDRAM”

“”The DDR4 SDRAM is a high-speed dynamic random-access memory internally configured as sixteen-banks, 4 bank group with 4 banks for each bank group for x4/x8 and eight-banks, 2 bank group with 4 banks for each bankgroup for x16 DRAM.
The DDR4 SDRAM uses a 8n prefetch architecture to achieve high-speed operation. The 8n prefetch architecture is combined with an interface designed to transfer two data words per clock cycle at the I/O pins. A single read or write operation for the DDR4 SDRAM consists of a single 8n-bit wide, four clock data transfer at the internal DRAM core and eight corresponding n-bit wide, one-half clock cycle data transfers at the I/O pins.

The “old” standard, DDR3, from way back in 2010 was “The DDR3 SDRAM is a high-speed dynamic random-access memory internally configured as an eight-bank
DRAM. The DDR3 SDRAM uses a 8n prefetch architecture to achieve high-speed operation. The 8n prefetch architecture is combined with an interface designed to transfer two data words per clock cycle at the I/O pins. A single read or write operation for the DDR3 SDRAM consists of a single 8n-bit wide, four clock data transfer at the internal DRAM core and eight corresponding n-bit wide, one-half clock cycle data transfers at the I/O pins.”

While the transfers may be similar, the top end is planned to be 3.2 gigatransfers per second per pin, twice as fast as the original DDR3 (now increased to 2.1 gT/s). However you slice it, this will make possible more throughput in a system. It’s not likely to appear in smartphones soon, though.

About Robert Pogson

I am a retired teacher in Canada. I taught in the subject areas where I have worked for almost forty years: maths, physics, chemistry and computers. I love hunting, fishing, picking berries and mushrooms, too.
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