"MTM" stands for Machine Type - Model. On ThinkPads before the T440 generation, it is a 7-character code often found on a sticker on the bottom of the systems that identifies the specification of that system.
The first 4 characters is the Machine Type consisting of digits only, and the last 3 is the Model consisting of alphanumeric characters. For example, 6363-P3U is the MTM for an X60 Tablet.
For the longest time, IBM's, and then Lenovo's support website provides the feature of searching for specifications by MTM. By typing the MTM into a search box, I can see the specs of that X60t as it left the factory:
L7400(1.5GHz), 1GB RAM, 80GB 5400rpm HD, 12.1in 1024x768 LCD, Intel 950, Intel 802.11abg wireless, Modem, 1Gb Ethernet, Secure chip, Fingerprint reader, 8c Li-Ion, WinXP Tablet 2005
But Lenovo's 2014 support site is removing that functionality for many legacy systems. For now, the old support site can be found at http://support1.lenovo.com, but that site may be decommissioned soon.
What will future people do when they want to see their vintage ThinkPad's original configuration? Fear not, the entire ThinkPad MTM database from Lenovo's website, as it was available Oct. 27 2014, has been backed up here!
(2021-09-30: Updated links. It looks like an update to Google Drive made the old links invalid.)
Click here to download a zipped Excel spreadsheet containing the entire ThinkPad MTM database
The spreadsheet is created with Excel 2010, and should be compatible with Excel 2007 upwards. I have not tried Open/LibreOffice.
The file is LARGE! It contains 552375 records, so be prepared.
To search for a specific MTM, just filter on the Machine Type and Model columns.
Here's a zipped CSV file of the database scrape, for people who like to play with the raw thing. The file is encoded in UTF-8 without BOM: this is important because of the occasional Unicode character (mostly nonsense). Newlines in the description field has been stripped out because many software trip over that kind of thing.
The scraped database here does not include the models listed below:
'ThinkPad T Series laptops', 'ThinkPad T440', '20B7'
'ThinkPad T Series laptops', 'ThinkPad T440p', '20AW'
'ThinkPad T Series laptops', 'ThinkPad T440s', '20AR'
'ThinkPad X Series laptops', 'ThinkPad X230', '2325'
'ThinkPad X Series laptops', 'ThinkPad X240', '20AM'
Because they were already not available (504 Gateway Time Out) when the database is being scraped.