High Density DDR SDRAM Memory - upgrade or low-grade?

High Density DDR SDRAM Memory - upgrade or low-grade?

In this context High Density memory means the non-ECC 1 GB 184 pin SDRAM PC3200 DDR-400 memory sticks that have become so common on Internet auction sites.  The non-ECC bit must be emphasized here because High Density ECC PC3200 server memory is made by a number of perfectly respectable manufacturers and there are no problems with this when used as intended.  Note that whenever you purchase a High Density Stick from me it is clearly labled!

How RAM is organised

There's a great deal of misunderstanding about just how SDRAM is organised and what the numbers mean so we'll clear this up before continuing:

PC3200 is DDR SDRAM specified to operate at 200 MHz using DDR-400 chips with a bandwidth of 3,200 GB/s.  As DDR stands for Double Data Rate this means that the effective clock rate of PC3200 memory is 400 MHz.

1 GB PC3200 non-ECC sticks are usually made with 16 512 Mb chips, 8 down each side (512 Mb x 16)/8 bits = 1024 Mb.  The individual chips making up a 1 GB memory stick are usually organised with 64M bits and a data width of 8 bits, commonly expressed as 64M x 8.  Memory manufactured in this way is LOW DENSITY RAM and will usually be OK with any motherboard specifying PC3200 DDR-400 memory.

As the price of Low Density PC3200 DDR RAM has soared, however, an increasing number of people - usually sellers on auction sites - have been offering High Density PC3200 DDR-400 non-ECC RAM for sale at temptingly low prices.

What is High Density RAM?

Again in the context of the 1 GB non-ECC PC3200 SDRAM stick there is very little visually to differentiate Low Density from High Density RAM.  High Density DDR RAM sticks will, like their Low Density counterparts, usually be double sided with eight 512 Mb chips per side.  The difference is that each chip, instead of being organised in a 64M x 8 configuration is organised with 128M bits and a data width of 4 bits, or 128M x 4.

Most High Density PC3200 modules are assembled using Samsung chips.  These chips come in both the familiar 22 x 10mm (approx) TSOP2 and smaller squarer 12 x 9mm (approx) FBGA package sizes.  High density Samsung chips can be identified by the numbers on each chip.  If the sixth and seventh characters are "04" (for example K4H510438D-UCCC) then the chips are x 4 and High Density.  If the sixth and seventh characters are "08" then the chips are x 8 and Low Density.

Does the difference between High density and Low density RAM matter?

The answer as far as most people are concerned is yes.  High Density non-ECC PC3200 is a non-standard configuration and to date no mainstream manufacturers make these modules.  Some high density PC3200 sticks are sold on auction sites as Samsung memory, however these modules are not made by Samsung.  They're unbranded and assembled using Samsung memory chips.  Just because my car has a Mercedes engine doesn't make it a Mercedes!  So the first issue is if using unbranded memory bothers you, steer clear.

More important however are compatibility issues.  Because High Density non-ECC PC3200 modules are non-standard not all motherboards work with them.  Some do, some might and some definitely don't.  Boards expecting memory to come in 64M bit high and 8 bit wide chunks don't always take kindly to memory served 128M bits high and 4 bits wide.  Some motherboards recognise high density 1 GB modules as only 512 Mb, in other cases motherboards refuse to POST.  One of the problems of determining compatibility is that unlike the best branded modules, where you're paying for consistency and testing, unbranded modules can exhibit inconsistency from module to module, so that one 1 GB stick of High Density non-ECC RAM might work fine on a SIS 755 based motherboard while a supposedly identical stick will cause a POST failure.

What works and what doesn't...

The following list comprises most of the motherboards stated to work with non-ECC High Density PC3200 memory.  Though bear in mind that whether your particular board works with High Density RAM, and if it does, whether it will work with all slots filled with High Density RAM will always be something of a punt:

INTEL 915; NVIDIA NFORCE3 250GB; NVIDIA NFORCE4 SLI; SIS 645; SIS 648; SIS 648FX; SIS 650; SIS 650GX; SIS 655; SIS 661FX; SIS 746FX; ULI CHIPSETS; VIA K8T800; VIA KM333; VIA KM400; VIA KT266; VIA KT333; VIA KT333A; VIA KT400; VIA KT400A; VIA KT600; VIA KT880; VIA P4X266A; VIA PM800; VIA PT800; VIA PT880.

The following additional boards might possibly work with some High Density modules - but equally they might not:

SIS 649; SIS 651; SIS 656; SIS 661; SIS 748; SIS 750; SIS 755; SIS 756; VIA APOLLO P4X400; VIA K8M800; VIA K8M890; VIA K8N800; VIA K8N890; VIA K8T890; VIA K8T900; VIA P4M800 PRO; VIA P4M890; VIA P4M900; VIA PN800; VIA PT800; VIA PT890.

As a rule of thumb it seems safest to assume that no Asus or Intel boards (with the exception of the 915) will work with High Density RAM.