Can you enlighten me which aspects are typical for pre-production units?
It depends on where in the development process it is.
Early hardware sometimes has odd-colored or odd-finished chassis parts. An example of this would be the glossy finish on the body plastics of some of the laptops at this year's (and previous years') CES displays.
Another indicator is model designations. While the X1 in the shots don't display this, some of the protoypes that crop up on eBay and similar from time to time have either incomplete or otherwise-odd model names. An example of this was the X300 prototype that I found on eBay a while back: it had an S__ model (I can't recall what the actual string was, but it wasn't X300.)
The most common sign of non-final hardware is the label that you see on a lot of review units: "Not a customer ship-level system". That's pretty self-explanatory, although based on what I've seen the review units that you see that on are usually pretty close to final.
The X1 in the shot also lacks FCC IDs for all of its transmitting components, which means that it's *definitely* not ready for production or sale; the FCC tends to get more than a little irritated if you sell wireless devices without adhering to federal regulations. In fact, the underside is the best giveaway (assuming the photos aren't doctored). The factory ID is missing, the FCC IDs are missing, the text after "Lenovo" is a placeholder, and the model number is what appears to be a hardware revision identifier as opposed to the usual 4-3 model/type grouping. The sticker beneath the serial number sticker is also -- if my guess is correct -- an internal identifier, probably identifying the product, revision/development stage, and providing a unit identifier. (I'm guessing on this part based on what I know about other manufacturer's product development process.)
Oh, and a serial number that isn't publicly recognized by any of Lenovo or IBM's tools is also a good indication that something interesting is going on. Even review units often are recognized by most of the SN lookup tools -- so a system that doesn't exist according to them is at least moderately unusual.
Internal hardware that carries identification of the source of the part is also a sign, although probably less of one for Lenovo than, for say, Apple. (With Apple, internal hardware almost never carries corporate origin marks. The batteries, for example, will list Apple-specific information and a country of origin, but that's about it. Pre-production batteries, on the other hand, identify the manufacturer and/or cell information.) With the X1 in the shots, the WLAN card is notable; Lenovo's cards are semi-custom (Lenovo-specific ID and labels with the part + FRU info.) In the photo, the WLAN card doesn't have a normal label, but instead has the same label that the underside of the machine has. I'd assume this is because the proper labels aren't finalized yet.
In the X1 shot, the battery has part/FRU numbers... but they don't seem to exist anywhere: not on Lenovo's support pages, not in their (public) parts ordering system, and not anywhere on the web.
The power brick has got a "not for sale" badge, missing regulatory markings, and a build date. 'nough said. (Good to see that Delta's doing the power supply though!)
Speaking of obvious giveaways: the WWAN card has a "prototype", "not type approved" label. To my untrained eye that indicates it's a prototype.
So in summary: we have shots of a machine with a "nonexistant" serial number, no proper model designation, numerous odd ID stickers, a host of missing regulatory markings, labels with placeholders, and several components with missing or never-before-seen FRUs.
Yeah, it's pre-release hardware.
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