Lennart Sorensen wrote: > I wonder how much confusion M.2 is going to cause given > some devices are PCIe based and others are SATA based, > and some boards only support one or the other, while many > do support both.
Very few issues with PCIe v. SATA when it comes to M.2. I.e., - Virtually all M.2 notebooks have at least one (1), dual-keyed B-M socket - Virtually all notebooks have all their M.2 B-M sockets wired to SATA - Virtually all notebooks have at least one (1) M.2 B-M socket wired to PCIe - Virtually all M.2 storage cards are also dual-keyed for B and M (x) At most you might be in trouble on low-end notebooks where you buy a 2nd M.2 PCIe-based card and find out you're already using the only slot that offers PCIe. SIDE NOTE: Some notebooks have a M.2 E socket. Although this has a PCIe (x2) connection (like it's prior Mini-PCIe), it also has an UART, so it's used for the WLAN + optional Broadband function. It's usually also shorter too (22x30 or 22x42mm). BUT ... the _bigger_ issue ... back ON-TOPIC, LPI-wise ... is NVMe. Unlike AHCI, which everything supports regardless if it's PCIe or SATA, is NVMe _requires_ the "full stack" to support boot. It's almost exactly like why one has to use uboot, because there's no legacy block boot compatibility like AHCI (which can fall back to legacy ATA/IDE too). Hence why I said ... AHCI v. NVMe is the bigger consideration for LPI. It's also why I'm holding off on getting a new notebook and M.2 devices _until_ they are _native_ NVMe. And that doesn't happen until the native PCIe 3.0 + NVMe controller logic and firmware is actually in the NAND controller in and inherent to the package itself. So far _all_ M.2 designs have been legacy NAND controllers, and for PCIe support, they use an external (often fab'd at 65-90nm, with associated thermal issues) PCIe 2.0 bridge. This is why I've been holding off. mSATA v. M.2 SATA is *0* difference, other than 30x50mm mSATA (1,500mm^2) tends to still have "more usable real estate" than even 22x80mm (1,760mm^2) M.2. And even M.2 PCIe using AHCI today doesn't offer much over M.2 SATA. It's NVMe that will change everything. Because NAND isn't about throughput ... it's about read-only access-times. And when you can queue up hundreds of reads (NVMe) instead of only two (AHCI), and you can better control the flow, it will be a whole different ballgame. -- bjs _______________________________________________ lpi-examdev mailing list lpi-examdev@lpi.org http://list.lpi.org/cgi-bin/mailman/listinfo/lpi-examdev
