PC720 6860 was introduced to the market together with PC750 6886 in 1995. 6860 is not a Pentium based PC. IBM Japan didn't introduce PC730 6876 in Japan, instead they made this unique space-saving desktop model. PC720 6860 is a strange *hybrid* PC with one MCA slot, one shared MCA/PCI slot, and a ISA-like slot for PCMCIA /A exclusively designed for this box.
Type JZG was equipped with a PS/55 Display Adapter /NI-J and DOS J5.02Z (JDOS).
6860/6869 Planar (DX4-100 model)
J2 is silk screened as "IR/PCMCIA". It's obvious that PCMCIA is meant for a 2nd PCMCIA device which could be installed at the front end. I've believed for a long time that IBM only planned to develop such a device, and that they never made it. That was until I got my 6869-J4K (ISA DX4-100 model which is not listed in my PC Guide Book). J4K has additional PCMCIA slot just below the FDD bay which you can see in the picture at the top of this page. And what does "IR" mean? It's likely for some sort of IrDA device. No clue if it was ever released for the PC720.
Planar can take a DX2-66, DX4-100 or PODP5V83. No interposer required to use 3.3V CPU's. In order to use PODP, BIOS should be updated to KOJT66JP. See below.
PODP (& Win95)
The PODP Support Diskettes Kit consists of 3 parts:
J55 - Voltage select
For 5V CPU close 2x3 jumper blocks near to the PSU connector.
J14 - CPU select
For 486DX set jumper to position 2-3 (default).
Other Jumper Blocks
J19 - purpose unknown. Default is 1-2 closed.
The planar has 4 SIMM slots and takes 4, 8, 16, or 32 MB, 70 ns, FP, parity modules.
S3 Vision 864 1MB (2MB for J4G model). Win95 recognize the chip with it's built-in driver.
JZG model doesn't use onboard S3 Vision but use a PS/55 DBCS Display Adapter/NI-J together with pre-installed DOS J5.02/Z (specialized DOS J5.02 for this model).
Hard Drive Interface
Only one IDE channel is provided. There are solder pads for 2nd IDE
channel on the planar, but even if the 2nd channel could be activated, there is
no room for 3rd IDE drive.
Hard drive runs in MS-DOS Compatibility Mode Under Win95
Win95 will load "standard IDE/ESDI hard disk controller" with configuration #1 which has IRQ value fixed to 15. Change the configuration to #0 which has IRQ 14, all drives will work properly.
A genuine optional 2x speed CD-ROM (you can see it in the picture at the top of this page) is # 85G7285. I have a 4x slim drive for Toshiba laptops.
Same socket as in 9577i or 9585 is used. L2 cache module is P/N 85G4865 "128KB L2 Super Cache". This module can be used for M70/80 PowerBoard. To say the truce I bought my 1st 6860 in order to get a cache module in it. The DX2-66 model does not have the cache socket.
I've never seen this type of connector in any other PC. IBM Japan made only
2 adapters for this interface:
All models other than JZG use same Riser Card which has PCI/MCA shared slot x1, MCA slot x1 and one ISA style slot for 2Slot PCMCIA/A (P/N 54G0547). Riser Card for JZG doesn't have a PCI slot but it has one more MCA bus slot for PS/55 Display Adapter /J which locates under connector J6 (opposite side of PCI slot J5). I'm not sure but probably J1 is for Enable/Disable selector for PS/55 display adapter. Outline below is the one for models other than -JZG.
2 slot PCMCIA /A with ISA style connector is equipped in all models. ISA
models (6869 and 6883) also use same adapter. Win95 built in driver can't
handle this adapter properly on MCA models but the very same adapter installed
in ISA models can be used without any problem under Win95B or Win98.
Max. power consumption: 70W
6860 has a very unique PSU. The cooling fan will slow down if the total system power is lower than 50W, and will stop to spinning completely if bellow 30W. Thus the cooling fan usually stays idle. When I got the 6860 I've immediately noticed that the fan wasn't running at all. As I didn't know about this unique feature I thought there must be some fault on the circuit board of the PSU. I disassembled PSU and soldered 12V line directly to the fan assembly. Only latter on have I learned about this unique function. The jumper wire is still there... Some machines have input AC voltage selector. Mine has a "fan mode selector", summer mode with direct connection and winter mode with original connection.
Mine works fine under DOS. But under Win95B it usually freeze at start up after the Win95 logo appears on the screen. I solved this symptom by modifying MSDOS.SYS to have a start up menu with default boot for Win95 after 60 seconds of delay time to boot. Maybe mine needs some delay for stable DC output for planar, a hard drive and a CD-ROM. I'm sure that this symptom is not related to the above mentioned fan cable modification, 'cause I have the same problem even when I switch back to the original cable connection.
6860 is not an IML machine, but it does support service partition