Crucial (Micron) server memory - single new 512MB stick. Form factor 184-pin DIMM module. DDR3 DDR-400mhz PC3200 CL3. 

Memory has Full ECC error correction and is unbuffered. This is server memory, not intended for ordinary user desktop PCs (unless the PC's motherboard supports ECC).

Crucial part # CT6472Z40B 
Micron chip spec # MT9VDDT6472AG-40BD1 200550
Brand-new in generic OEM packaging and free shipping in the US or Canada.
Fully guaranteed.