Memory

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SIMM

Module sizes

Pins	Data Bus Width [bits]
30	8/9
72	32/36

Note: Parity vs Non-parity modules

RAM technologies

DRAM type	Description	Note
FPM	Fast Page Mode
EDO	Extended Data Out	5% faster than FPM if supported

SO-DIMM

SO-DIMM=Small Outline DIMM

SO-DIMM is a smaller than DIMM to fit in notebooks etc.

Pins	Data Bus Width [bits]
72	32
144	64
200	72

DIMM

DIMM modules are sold according to clock speed (MHz), bus speed (mega-transfers per second), and transfer rate (megabytes per second).

SDR SDRAM DIMM/SO-DIMM

SDRAM=Synchronous Dynamic RAM.

SDRAM is a variant of DRAM in which the memory speed is synchronized with the clock pulse from the CPU.

This synchronization enables the SDRAM to pipeline read and write requests. Pipelining enables the SDRAM to accept commands at the same time as it is processing other commands.

3.3 V

DIMM Module	Chip Type	Clock Speed [MHz]	Bus Speed [MHz]	Transfer Rate [MB/s]
PC66	10ns	66	66	533
PC100	8ns	100	100	800
PC133	7.5/7ns	133	133	1,066

Module	Pins
DIMM	168 pin
SO-DIMM	144 pin

DDR SDRAM DIMM/SO-DIMM

DDR SDRAM=Double Data Rate SDRAM.

DDR SDRAM is an improvement over regular SDRAM, also known as SDR SDRAM (Single Data Rate SDRAM).

DDR SDRAM doubles the bandwidth of SDR DRAM by transferring data twice per cycle on both edges of the clock signal, implementing burst mode data transfer.

2.5V

DIMM Module	Chip Type	Clock Speed [MHz]	Bus Speed [MHz]	Transfer Rate [MB/s]	Note
PC1600	DDR200	100	200	1,600	¹⁾
PC2100	DDR266	133	266	2,133	¹⁾
PC2400	DDR300	150	300	2,400
PC2700	DDR333	166	333	2,667	¹⁾
PC3000	DDR366	183	366	2,933
PC3200	DDR400	200	400	3,200	¹⁾
PC3500	DDR433	216	433	3,466
PC3700	DDR466	233	466	3,733
PC4000	DDR500	250	500	4,000
PC4300	DDR533	266	533	4,266

Note: ¹⁾ Standardised by JEDEC

Module	Pins	Power dissipation
DIMM	184 pin	5.4 W
SO-DIMM	200 pin

DDR2 SDRAM DIMM/SO-DIMM

DDR2 SDRAM is the second generation of DDR SDRAM.

DDR2 SDRAM improves on DDR SDRAM by using differential signaling and lower voltages to support significant performance advantages over DDR SDRAM.

Differential signaling requires additional contacts, so the number of contacts on a DDR SDRAM DIMM module was raised from 184 to 240. The voltage of DDR SDRAM DIMM's was lowered from 2.5V to 1.8V. This improves power consumption and heat generation, as well as enabling more dense memory configurations for higher capacities.

1.8V

DIMM Module	Chip Type	Clock Speed [MHz]	Bus Speed [MHz]	Transfer Rate [MB/s]	Note
PC2-3200	DDR2-400	200	400	3,200	¹⁾
PC2-4200	DDR2-533	266	533	4,266	¹⁾
PC2-5300	DDR2-667	333	667	5,333	¹⁾
PC2-6400	DDR2-800	400	800	6,400	¹⁾
PC2-8500	DDR2-1066	533	1066	8,500

Note: ¹⁾ Standardised by JEDEC

Module	Pins	Width [mm]	Height [mm]	Power dissipation
DIMM	240 pin			4.4 W
SO-DIMM	200 pin	67.6	30.0
FB-DIMM				10.4 W
Micro-DIMM	214 pin	54.0	30.0

DDR3 SDRAM DIMM/SO-DIMM

Same pinout as DDR3?

1.5V

DIMM Module	Chip Type	Clock Speed [MHz]	Bus Speed [MHz]	Transfer Rate [MB/s]
PC3-6400	DDR3-800	100	400	6,400
PC3-8500	DDR3-1066	133	533	8,533
PC3-10600	DDR3-1333	166	667	10,667
PC3-12800	DDR3-1600	200	800	12,800
PC3-14900	DDR3-1866	233	933	14,930

Module	Pins	Width [mm]	Height [mm]
DIMM	240 pin
SO-DIMM	200 pin	67.6	30.0
Micro-DIMM	214 pin	54.0	30.0

VLP DIMM [Registered / Unregistered]: 8.3mm [H] x 133.35mm [L] [Height x Length]
VLP FB-DIMM: 18.29mm [H] x 133.35mm [L] [Height x Length]
VLP Mini-DIMM: 18.28mm [H] x 82mm [L] [Height x Length]

VLP DIMMs 184-pin, 240-pin, VLP MiniDIMM; 244-pin

244 pin Mini-RDIMM Form Factor ??

Micro-DIMM

Delivers highest memory density of all modules on smallest space
30% DIMM size reduction
35% space on board reduction compared to SO-DIMM
JEDEC compliant
Mezzanine connector
214pins, FBGA

Memory sizes

256MB
512MB
1GB

Memory speed

PC2-3200 (DDR2-400)
PC2-4200 (DDR2-533)

168 Contact DIMM's

The earliest DIMM's were of the 168 contact variety. These DIMM's have come in a variety of configurations. It is possible to determine the configuration of the DIMM by examining the placement of notches on the bottom of the DIMM.

DIMM Notch Key One
Position	Meaning
1	Reserved
2	Buffered
3	Unbufered

DIMM Notch Key Two
Position	Meaning
1	5.0V
2	3.3V
3	Reserved

Corsair FAQ

I've heard of PC1600 and PC2100. What does this mean, and what is the difference? Well, it's kind of like PC100 and PC133. Since it is double datarate, you might expect that DDR would be PC200 and PC266. In fact, the RAM chips themselves are sold as PC200 and PC266. HOWEVER, us module guys did not want you to think that Rambus (at 800 MHz) is four times as fast as PC200 DDR. So, we went with a number that reflects the MODULE bandwidth. Since DDR DIMMs are eight bytes wide, the designation becomes PC200*8 = PC1600 and PC266*8 = PC2100. So, to repeat, PC1600 uses both edges of a 100MHz clock, and PC2100 uses both edges of a 133MHz clock. And now, you're only a little less confused than me!

FAQ

Can I run PC3200 memory in a PC1600 computer?

Yes. Underclocking at PC1600 speed is alright.

Can I run PC1600 memory in a PC3200 computer?

Maybe?

Links