I was going to open up my NEO unit to see what's inside. But, fortunately, people have already done that. There is a CR2032 coin-cell inside that serves as backup to retain SRAM while the AA batteries are removed. Some power users have opened their units to replace the lithium backup battery, and photographed the innards.

https://www.flickr.com/photos/83235901@N00/5347018436/

https://www.flickr.com/photos/83235901@N00/5346409483/

http://imgur.com/gx9aJdX

So, what have we here? Well, there's...

• Probably serial header at J1
• Main processor: DragonBall VZ "MC68VZ328PV" (or AG) with markings "6K85Z" and "QQAN0433"
  • This is a DragonBall VZ SoC - a 32-bit processor implementing the Motorola 68k architecture, and common in early PalmPC offerings before they switched to ARM.
  • Datasheet: http://pdadb.net/index.php?m=processor&id=177&c=motorola_dragonball_vz_mc68vz328&d=detailed_specs
• Some NOR or NAND flash, by ST Microelectronics by the look of it. The label on top may be a serial number or mfg. date for NEO boards.
• Something unknown: "ISP1161ABD CD0991 4 TPG0 424D"
  • Turns out this is a USB 1.1 Host/Device controller. Clearly, it handles both the NEO <-> PC chatter, as well as the NEO -> Printer ability.
  • Datasheet: http://www.mouser.com/ds/2/302/ISP1161A1-03-196942.pdf
• Something else unknown: "SEC 416 EF70 K6F401 6U6G"
  • This appears to be a low-power CMOS SRAM.
  • Datasheet (similar): http://www.datasheets360.com/part/detail/k6f4016u6g-ef70/-63573262713609055/?alternatePartManufacturerId=0

Based on how the device functions: the system appears to store the OS and applications on the flash chip, do all computation using the processor within the SoC and attached SRAM temp area, and store the users' writing on the SRAM too. This makes a lot of sense, because the device is from the Early Days of flashmem, and it would be smart to limit the number of writes to the chip - like, don't save every time a key is pressed. Also, if the batteries run out, the OS and apps won't disappear : )

Disappointingly, it doesn't appear possible to give space to the text editor at the expense of apps. They live in separate RAM environments. Scratch that long-requested feature off the list.

The USB opens up possibility to read and write to an external drive...

When you install the NEO Manager software, it unpacks a number of files of format ".os3kapp". These are the SmartApplets that you can install to the device. Now that we know the CPU architecture, and we have local dumps of the applications, maybe it's time to dig up a 68000 disassembler.