An investment in a new piece of machinery is a costly business. Even before your intitial cost is realized, a newer, better version of the machine will become available.
OEMs choose to stick with older machinery in an effort to realize the sunk cost. This has some drawbacks. When there's a line down, engineers and purchasing agents are faced with the task of finding a replacement part. For obsolete electronic components and components with limited stock, OEMs must choose between two options: pay a high price or find a suitable alternative.
DDR SDRAM is one class of memory ICs. The DDR1 SDRAM has been replaced by newer versions, the DDR2 SDRAM and the DDR3 SDRAM. Neither part is forward or backward compatiable, meaning that the newer parts cannot be used in place of the older component and vice versa.
Currently, EarthTron has several Micron Technology DDR SDRAM pieces available for sale: