SD Card slot
PCI-based SD Card slot
This implementation is called "SD Card with IO support", and supports in addition to regular SD memory cards also special SDIO cards (e.g. Bluetooth, WiFi, etc).
lspci reports it as a Ricoh device with PCI ID 1180:0822 (X Series, Z60m, Z60t), or 1180:0841 (Z Series).
The sdhci project has developed a driver that supports these and other SD controller chips. The driver has been reported to work on ThinkPad X40, X41, Z60m, Z60t, X60 and X61 models, and has been available in mainline kernel since 2.6.17-rc1. See also "How to get the internal SD-CARD working".
It works with SDHC cards too (at least on my X41 Tablet and linux 18.104.22.168).
On X41 Linux 22.214.171.124 can read/write to existing partitions on 16 GB SDHC (FAT32), 4 GB (non-HC, FAT32) and 2 GB (non-HC, FAT16) cards. However, deleting, creating, resizing or formatting partitions does not work. (All operations do work on all cards when using an external USB SDHC card reader instead of the internal one. All operations work under Windows XP and Hotfix 934428 with the internal card reader so this is not a hardware issue.)
A Microsoft hotfix is available here  that adds SDHC (SD High Capacity) support to Windows XP SP2 systems.
Models featuring this Technology
- ThinkPad X40, X41, X41 Tablet
- ThinkPad X60, X60s, X60 Tablet, X61, X61s, X61 Tablet
- ThinkPad Z60m, Z60t
USB based SD Card slot
This implementation only supports SD Memory cards.
Should be supported by the Linux USB Storage drivers (usb-storage).