These are Kingston ValueRAM 512MB 533MHz unbuffered DDR2 modules. They'll work in pairs in dual-channel systems, like current DDR400 setups. Check out the second picture for a comparison to a DDR400 DIMM. DDR2 has 240 pins, up from DDR's 184 pins. The chips on the DIMM, as evident in the last picture there, are made by Elpida. Kingston is careful to point out that these DIMMs are early samples, and some specs may change before production motherboards ship in volume. The company is working with JEDEC and Intel, among others, to ensure compatibility.
DDR2 memory is tweaked with internal timings more conducive to higher speeds, plus on-die termination to aid signal integrity. DDR2 promises speeds, eventually, up to 667MHz, and about half the power consumption of current DDR memory. We should see Pentium 4 chipsets and mobos with DDR2 support in the coming weeks and months, but the Athlon 64 probably won't make the leap for a while yet, as we've reported before.
We'll take these puppies for a spin as soon as we have a mobo to use with 'em.