The ThinkPad 720 and 720C systems come with 4MB of 80nS memory, expandable to a maximum of 16MB through the use of  IC DRAM cards of 2MB, 4MB or 8MB.
   The 4MB of memory is on the reverse side of the memory card socket. If you remove the bottom of the case, flip up the memory card socket and you will see the row of eight flat chips, similar to those on the 9533.

   The cpu is an IBM 486SLC2 50/25MHz (16KB cache), and a math coprocessor socket for a 25MHz 80387SL is on the bottom of the system  An optional 240MB HDD is also available to contain large operating systems and application requiring a large storage space.

INTEGRATED POINTING DEVICE
   TRACKPOINT II:  The  720 and 720C has a TrackPoint II  built into the keyboard.  It works like the mouse and allows the user to point and select icons on the screen under control of the application.  It consists of a device that stands between the "G" and "H" keys, accompanied by two "Click-Buttons", which are positioned below the space-bar.  The device reacts to pressure from the finger-tip and the left button is used for selecting or dragging items on the screen. The right button simulates the Enter key in some applications.

ThinkPad 720 Planar Front

J6 Serial Connector J7 Parallel Connector J8 System-Expansion Connector (240-pin) J10 PS/2 port (Mouse/KB) J11 PCMCIA card interface J12 Base Memory Card Interface J13 Video Card Interface J14 Backup Battery Connector J16 Hard Disk Drive Connector

J15 Processor Card Interface JMP1 ?? PCMCIA PCMCIA Connector S1 Password-override switch U14 BIOS 59G3639 U15 48G8905 U21 NS PC8477BVF-1 Floppy controller Y4 14.138 MHz osc

There are upgrade BIOS chips available. More as I find out.

JMP1  This resembles the small, short jumper headers on the bottom of hard drives. What does it do? I haven't a clue...

Remove 720 / C Power-on password
   1. Power-off the computer. 
   2. Remove the battery pack and the bottom cover. 
   3. Locate the password-override switch on the system board. (See 'System Board (720, 720C)) 
   4. Slide the password-override switch to the left  position. 
   5. Power-on the computer and wait until the POST ends. 

Slide the password-override switch to the other position when service is complete. 

ThinkPad 720 Planar Rear

J1 System Status Indicator Connector J2 Keyboard Control Card Interface J3 Voltage Converter Interface J4 Speaker Connector J5 Diskette Drive Interface U1 39G8788 U3 34G3547 Used on the PCMCIA /A

U4 95F3690 U7 59G3249 U12 Dallas DS1485S RTC S1 Password-override switch Y1 24.000 MHz Osc Y2 10.000 MHz Osc Y3 32.768 KHz Osc

     1 External Display Connector
     2 LCD Connector
     3 System Board Connector
     4 Communication Adapter Connector
 

o   The ThinkPad  720  monochrome  model  does  not  support  the attachment of PS/2 monochrome displays.

Voltage Convertor

1 Power Jack 2 Battery Pack Interface 3 System Board Interface

4 Standby Battery Connector  5 Suspend/Resume Switch

Test 720 Voltage Convertor

   These interfaces were designed by the Swedish company Onsite in about 1995.  There seems to be some interest in these, and there are about 500 unpopulated flex PCB's left, so they may put back into production (the remaining 500 only) at some point. These were used in replacement plug-in drives sold to corporate customers (@$1200+ in 1995!).
   These kits can be used in the 700, 700c, 720, or 720c. However, this requires a upgrade BIOS 

   The strange 'round-down' scenario is a function of the controller chip passing specific hard-coded geometry parameters to the bios. It was easier to modify the bios than re-do the chip as drive sizes increased. They all use the same cyl/sector count, but the head no. is 16, 32 or 64 for the 540MB, 1GB and 2GB sizes respectively. IBM never made any MicroChannel drives (Ed. ESDI?)  bigger than 160MB, and their 240 and 340 drives used a similar interface translation chip.