Have a look at this Dan......
Many only consider SPEED when purchasing memory and often neglect an important fact that memory DENSITY is actually even more important!
So why memory DENSITY is so important? Is it related to your system when upgrading? The answer is YES!
If your system is designed for accepting DDR (Double Data Rate) memories of 184pin DIMM (usually desktops) or 200pin SODIMM (usually laptops) built, for your system to fully recognise 1GB capacity per memory slot, you need to use 'Low Density - 64Mx8 config' 1GB module. If you use 'High-Density - 128Mx4 config' 1GB module, your PC may only recognise it as HALF the size at 512MB or most of the time it will not work.
How to tell if your 1GB module is a low or high density module?
* All low density 1GB modules are made with 16 chips (8 chips on each side) using 64Mx8 device.
* All high density 1GB modules are made with 16 chips (8 chips on each side) using 128Mx4 device.
It costs memory manufacturers almost the same to produce Low Density 1GB modules which have 100% compatibility with all systems on the market, comparing to producing high density 1GB modules. So why would manufacturers be so foolish to produce high density 1GB modules which only have 10% compatibility with systems on the market? The reason is simple, because high density 1GB modules are mainly manufacturing process rejects/seconds that cannot be made as a low density modules. It is very much like Intel CPU, those CPU that cannot be made as Pentium 4 CPU become a slower bus Celeron CPU instead, by a down-binning process.
High Density module is by far much slower than Low Density module at same speed rating say PC3200/DDR400. A lot of users have fallen into attractive CHEAP PRICE trap by High Density module sellers and have complained that they are either VERY SLOW and/or will not run at all and sellers won't accept return!
High density modules are FAR CHEAPER, less than half the price when compare with low density modules and hence high density modules will NOT work on 90% of today's PC chipsets that require and can only use 'Low Density - 64Mx8 config' 1GB modules.
* LOW DENSITY modules have 100% compatibility with ALL systems and ALL chipsets.
* HIGH DENSITY modules only have 10% compatibility and are VERY SLOW.
This is also why almost all Branded-Name systems such as Apple/MAC, Compaq/HP, Dell and IBM only uses LOW DENSITY modules.
However 90% of eBay are plagued with High-Density 1GB modules at very low price, and you will be wasting your precious time and money having to return those high density 1GB modules to your seller for refund. So AVOID those 'High-Density - 128Mx4 config' 1GB modules which is usually UNBRANDED and is NO NAME!