1995 IBM PC Series 720: Looking inside (YouTube)
Hard Drive Interface
2-Slot PCMCIA Adapter
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.
||None (Socket is omitted)
||8MB (Max 128MB, 32MB x4)
||1MB (Upgradable to 2MB)
||3-Mode (1.44MB/1.2MB/720KB) x1
||PS/55 D/A NI
||PCI or MCA x1, MCA x1
|Small PCI NIC
|PC Card Slot
||Type I/II x2 or Type III x1 (ISA style PCMCIA /A)
|| 360 (W) x 370 (D) x 89 (H), 9 kg
||PC DOS J6.3/V, Windows J3.1
Type JZG was equipped with a PS/55 Display Adapter /NI-J and DOS J5.02Z (JDOS).
Model 6869 is an ISA version of PC720.
Model 6863 (also ISA) is named as "PC720" but it's a Pentium machine with P-100.
6863 uses same planar with PC750 model 6883 (probably sold only in Japan, planar is
different from that of 6885/6886 or 6887).
6860/6869 Planar (DX4-100 model) FRU P/N 85G7310, P/N 85G7235
J1 FDD Connector
J5 Power Switch
J11 PSU connector
J12 PSU connector
J14 CPU Select (SX/DX)
J19 Unknown (default 1-2)
J20 PSU connector (Power Good?)
J22 FAN (Solder pads only)
J23 L2 Cache Socket (DX4 models only)
J24 Riser Slot
J26 Small PCI slot 1
J27 pads for Small PCI slot 2
J37 Power & HDD LEDs
J44 VESA Video
J50 Frequency select (66/50 MHz)
J51 Mouse Enable/Disable
J52 FDD write Enable/Disable
J53 Clear CMOS (1-2: normal, 2-3: clear)
J54 Password Overwrite
J55 CPU voltage select
U7 Socket 3
U16 PC87323VULB Super I/O
U18 M33s0570-013 OKI/06H3669 IBM
U40 Unknown (heatsinked)
U42 Unknown (heatsinked)
U41 86C864P4 S3 Vision864
U53 86C716MG S3 SDAC
U55,56 DRAM sockets (video)
U57,60 KM416C256BJ-6 256Kx16 DRAM (video)
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.
J14 CPU type select
For 486DX set jumper to position 2-3 (default).
For 486SX set jumper to position 1-2.
J50 Output frequency select for programmable IC? (huh?) 1-2: 50, 2-3: 60.
J51-54 Default setting for these jumpers are all 1-2 closed.
J55 CPU voltage select
For 5V CPU close 2x3 jumper blocks near to the PSU connector.
For 3.3V CPU close 2x3 jumper blocks near to the CPU socket.
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:
- 6860ref.lzh Reference Diskette Ver. 1.10
- 6860diag.lzh Diagnostic Diskette Ver 1.11
- PC720SP.lzh System ROM update utility Ver. 1.10A (KOJT66JP)
Note: Win95 support program,
(dead), is not for 6860 but for 6863/6869 and other ISA models. 32bit PCMCIA
driver contained in this archived file is not usable on 6860. It's for
6863/6869 (and it may be for Win95A).
The planar has 4 SIMM slots and takes 4, 8, 16, or 32 MB, 70 ns, FP, parity
Uses the same style 128-pin L2 cache modules
as the Lacuna and
The original module is P/N
85G4865, marked as
"128KB L2 Super Cache". This module can be used for M70/80 PowerBoard. To say
the truth I bought my 1st 6860 in order to get the cache module from it.
The DX2-66 model does not have the cache socket.
S3 Vision 864 1MB (2MB for J4G model). Win95 recognize the chip with it's
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).
I've never seen this type of connector in any other PC. IBM Japan made only
2 adapters for this interface:
- SFF PCI Ethernet card, C/R 85G4854, equipped in 6860-J08
- SFF PCI TokenRing card, C/R?, equipped in 6860-J04. I want to see it!
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.
The drive interface is EIDE and it can handle drives larger than 524 MB.
I've used a 2.4 GB drive, and a 6.4 GB Seagate drive with 15 heads. Both worked
well. I've also tried a 8 GB Seagate drive, but it wouldn't detect it.
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.
Riser Card FRU P/N 85G7333, P/N 85G2105?
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.
J3,4 32-bit MCA slot
J5 32-bit PCI slot
U6 06H5423 (blue translucent QFP)
U8 10G7808 DMA Controller
Y1 24.0000 MHz osc
J1 Video /A selector? (default 1-2)
J2 Battery connector (CR2032?)
J6 ISA-style slot for PCMCIA /A
J9 PSU connector
U15 M91S028AT OKI/06H6468
U17 LH5168N-10L 8Kx8 SRAM (NVRAM?)
2-Slot PCMCIA Adapter FRU P/N 85G7334
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.
I tested a driver for Win3.1 "PC Card Director" on my 6860-J4G and I found
it could handle modem card. I've been using a 28.8Kb Double Jack Modem
Card under Win95B. PCMCIA device is not seen under Device Manager, but the card
securely detected in PC Card Director. I don't know if other cards such as NICs
or SCSI PCMCIA can be used.
Max. power consumption: 70W
Regular power consumption: 40W
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
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.
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.
6860 is not an IML machine, but it does support service partition (reference
partition?). My 6860 takes long time till the "Set Configuration" page comes on
the screen when I boot the system with the Reference Diskette. It stays quiet
while it reads configuration files as if the system froze. But from service
partition stored on the hard drive it goes straight into configuration