Posts by dave74737

MacBook Air now uses PCIe flash... but who'd Apple buy it from?

Form Factor + Price

I suspect I part of the decision was the available physical form factors from fusion IO. The smallest offerings right now are mezzanine cards for HP, Dell and Cisco blades (example: http://hp.fusionio.com/products/hp-io-accelerator-gen8/) . These are similar in size to the GPU cards in the pro machine from AMD, and there just wasn't the space to fit another similar device in the chassis. Fusion IO make use of an FPGA as their flash device controller, which is great in some ways, but does restrict the minimum size their devices can be. If you look at the size of the PCIe SSD they went with, its obviously an ASIC solution.

Finally there is the cost - fusionIO may be very capable, but it isn't cheap. The base cost per GB may have been just too high to include in a "mainstream" product. Why provide a rolls royce when a toyota will do?

Elon Musk vs NASA and the US rocket industry - ding ding!

Raptor is an LH2 / LOX Upper Stage

Raptor is not an engine - its a LH2 / LOX upper stage: See here: http://en.wikipedia.org/wiki/Raptor_(rocket_stage)

LH2 / LOX offers better ISP (essentially efficiency) than RP-1 (Kerosene) / LOX, but is costly to handle and degrades mass fraction because of its lack of density, which results in very large first stages.

Using RP-1/LOX for the first stage, and LH2 / LOX for the second stage makes a lot of sense - the second stage needs to carry less propellant and the density issue of LH2 is less of a problem as a consequence, and the efficiency of the second stage matters the most in terms of overall vehicle performance. Meanwhile the first stage can be less efficient, denser and more cost effective. Its a good combination - exactly why Wernher von Braun used it 45 years ago on the Saturn 5.

Dave.