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The Intel SSD is keyed for slots B and M, so it fits in the right slot. The Samsung SSD is keyed for slot M, so it won't fit in either of the Stream's slots. Wi-Fi and WWAN cards tend to use. When buying an SSD, be sure to purchase an M.2 drive that is exactly 42mm long, the only length that will fit in the ThinkPad T440s's narrow slot. Though M.2 is the next-generation of mSATA, it is. Notes on T450s (might also apply to T450): The 'Single-sided M.2 SSD, via M.2 card slot' is actually the cache drive under the battery and not one on the WWAN slot. And weirdly the HMM does not mention it at all. The actual WWAN slot does support SATA drives and bootable (according to other Reddit posts). Short of hacking the BIOS, or building a new type of USB 3.0 card from scratch, only WWAN cards will work in the WWAN slot. Yours may differ. Older Dell models did have SATA+PCIe in the WWAN socket, but this is not the case for more recent units. The story will inevitably be different for other manufacturers.
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This model has room for two possible drives.
(1) 2.5' bay caddy attached with NVMe extension cable circuit board to connect a 2280 SSD. I selected this option for the inclusion of that component which would otherwise have to be ordered separately if buying a traditional hard disk first. I will backup the drive image and restore to a larger SSD model.
(2) WWAN slot for a 2242 NVMe SSD. Lenovo only offered 128GB model for that slot, so I left it blank with intention to source for another SSD later.
And regarding the above point, I'm having a tough time locating any shop that even sells a 2242 NVMe SSD. All the rage is 2280, it seems. Can't find any good offerings on Amazon or Newegg either; practically are available 2242 models are SATA-based, rather than the NVMe the slot demands.
An ideal candidate I've seen is Western Digital PC SN520 but that apparently has sold out or only available through obscure channels. The only dedicated NVMe models widely available are China brands like KingSpec and Netac. They don't have enough mainstream popularity for people to actually buy and review them; so it's a long throw to guess their performance and durability.
Anybody else operating 'niche' hardware that call for the smaller 2242, 2230 form factors?
The melody of logic will always play out the truth.
~ Narumi Ayumu, Sprial
Most solid-state drives released within the last year or so have been too fast for the bus they're connected to. The 6Gbps SATA III spec was finalized in the days when rotational hard drives still ruled and SSDs were rare, ludicrously expensive, and relatively unreliable.
There are a couple of different standards that have been created to solve this problem, and they both solve it in the same basic way. One, SATA Express, uses the same physical connector as older SATA drives but uses PCI Express lanes rather than the SATA bus to boost storage speeds. The other, which will be more common in space-constrained mini-desktops, all-in-ones, and Ultrabooks, is called M.2 (previously NGFF, for 'Next-Generation Form Factor').
M.2 is interesting not just because it can speed up storage with PCI Express lanes, but because it can use a whole bunch of different buses too; it stands to replace both mSATA and mini PCI Express, two older standards that have been used for SSDs and Wi-Fi cards in laptops for a while now. Intel's new Broadwell CPUs and their chipsets include native support for M.2 and PCI Express boot drivers—neither PCIe-connected storage (hi Apple) nor the M.2 connector itself are new, but beginning with Broadwell systems each of those two things will become much more common.
Let's start with the physical connector and the things that connect to it. There's a lot to unpack, starting with the fact that there's more than one kind of M.2 connector, more than one type of interface that can be used with M.2, and more than one kind of M.2 card.
Getting to know M.2
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Pictured at the top of this article are four different M.2 cards. The one on the left is a combo Wi-Fi and Bluetooth card. The next one to the right is a Sandisk SSD that uses the SATA bus. The next one is an Intel SSD that also uses SATA. The one on the right is a Samsung SSD that can use up to four PCI Express lanes.
AdvertisementPay attention to two things as you compare and contrast these cards. First, the physical connector on each card is different; each card has different cutouts in the bottom and exposes different pins. Second, the cards are of different lengths and widths. All of this is accounted for in the M.2 spec (PDF).
The different connectors signify different M.2 'module keys.' Each key exposes a different set of interfaces to each card—M.2 can connect directly to the PCI Express bus, but different pins can be used to connect to the USB 2.0 and 3.0 buses, SATA III, DisplayPort, and a variety of other less-prevalent storage buses. Cards with one notch at the bottom are keyed for one specific kind of connector. Cards with two notches can be used in two different kinds of connectors.
Above is a picture of two M.2 slots on the motherboard of an HP Stream Mini. The slot on the left uses module key E, and the one on the right uses module key B. The Wi-Fi card is keyed for slots A and E, so it fits in the left slot with no problems. The Intel SSD is keyed for slots B and M, so it fits in the right slot. The Samsung SSD is keyed for slot M, so it won't fit in either of the Stream's slots.
| Key | Card measurements | Interfaces | Common uses |
|---|---|---|---|
| A | 1630, 2230, 3030 | PCIe x2, USB 2.0, I2C, DisplayPort x4 | Wi-Fi/Bluetooth, cellular cards |
| B | 3042, 2230, 2242, 2260, 2280, 22110 | PCIe x2, SATA, USB 2.0, USB 3.0, audio, PCM, IUM, SSIC, I2C | SATA and PCIe x2 SSDs |
| E | 1630, 2230, 3030 | PCIe x2, USB 2.0, I2C, SDIO, UART, PCM | Wi-Fi/Bluetooth, cellular cards |
| M | 2242, 2260, 2280, 22110 | PCIe x4, SATA | PCIe x4 SSDs |
The table above lays out the keys in common use today—there are others, mostly placeholders to be called into service as newer buses and interfaces are introduced.
Note the four- or five-digit numbers paired with each slot. These are actually codes to refer to the physical dimensions of each card; the first two digits specify the width in millimeters and the second two or three digits specify the length. Our Wi-Fi module is 16mm wide and 30mm long, or 1630. Two of our SSDs are 22mm wide and 80mm long, or 2280. The other SSD is 22mm wide and 42mm long, or 2242. All motherboard slots are 22mm in width, even the ones attached to 30mm-wide cards.
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All current keys can give cards access to two PCI Express lanes, but otherwise interface compatibility is all over the place—so far, it's been pretty easy to guess what kind of peripheral you're dealing with based on the key it uses. Wi-Fi and WWAN cards tend to use keys A and/or E, since they only need the PCI Express or USB 2.0 buses and only need 30mm in length to fit all their key components. SATA SSDs and SSDs that use two PCI Express lanes tend to use keys B and M to maximize compatibility, since both connectors can deliver both SATA III and two PCIe lanes. The very fastest SSDs tend to be M-keyed since it's the only one that delivers four PCIe lanes.
This is a lot to digest, but it's most of what you need to know to understand M.2. There are some other stipulations around the physical thickness of the cards that you can read about in the documentation, but they aren't as important to our discussion today.
The key system isn't always foolproof—our A- and E-keyed Wi-Fi module will physically fit into the B-keyed SSD slot even though the computer won't recognize it there. M.2 is certainly more confusing than the mPCIe and mSATA specs, but in the end it's more flexible. Components can access many different buses through one small internal connector, and you've got a lot of different physical card sizes to play with instead of being tied to either a 'full-height' or 'half-height' card.
The worst thing about M.2 right now is a general scarcity of components. OEMs buying parts directly from manufacturers probably have more choices, end users buying M.2 cards from Newegg or Amazon will find that they have few options, especially compared to the selection of mSATA and mPCIe components. That will change as M.2 goes mainstream and those older connectors begin to fade. Broadwell is a big step forward in that transition.