ARCO AC-107x

@6263.ADF Arco AC-1070 IDE Controller supports CD-ROM (rename)
@6263.ADF Arco AC-1070 IDE Controller Different brands (i.e. CMS Enhancements)
@62B6.ADF Arco AC-1079 SLIM Drive Adapter Allows Mirroring! DOS/Win 3.x, NT3.5,OS2,Novell 286/386, adf, MCAIDE

MCDROM Install IDE CDROM with HD, or alone

ARCO BIOS 3.03 '94
   Uses NS NMC27C64Q-150 8Kx8 CMOS EPROM 28-pin DIP

The 1070 is the early one piece card version, unlike the 1075, which has a detachable slot bracket. The 1075 will fit in the Integrated Drive controller slot on a 50/50z if you remove the single phillips screw in the upper right corner of the adapter.

ARCO in an 8550
BIOS Capabilities
CD-ROM on 1075
PIO Mode Only
Max Drive Size
ADF Sections

AC-1075 Rev C [P]

Peter said:
   That version uses 4 PALs (2x GAL16V8A, 1x GAL20V8A, 1x TIBPAL 20L8), 4x 74LS245, 1x 74LS374, 3x 74LS373 and 1x 74F04 + 1x 27C64-150 EPROM (8Kx8).

The main disadvantage on that controller is the off-standard I/O address. It will not be detected properly as IDE controller under e.g. Windows or with any OEM IDE driver under DOS. As far as I can tell from tracking the connections two of the PALs are used to set the adapter ID / POS and the other two are address decoders for the I/O range and the other decodes the ROM address.

Adapter ID detection could be easily done with 2 x 8-bit logic comparators, but you really don't need to do that if you'd opt for a "passive" card that just occupies a fixed I/O range and directly hooks to IRQ 14h. That card would be treated as a system board extension - just like a COM- or LPT-port. The only thing you need is a boot ROM that hooks into the PS/2 ABIOS routine and settles the first of the IDE HDs as "Hex 80" device - just like as if it were attached to an ESDI controller for instance.

It couldn't be that complicated. The most of the routines are already included within the IBM ABIOS. The complete handbook scans of the PS/2 BIOS are in the PDF download section on my pages.

Guess I need to copy the ROM content from the CMS / ARCO controller into my EPROMmer and dig a bit in it on how they did it. That controller is bootable and there must be an easy mechanism on how they hook the drive into the bootable devices list.

AC-1075 Rev D

J1 Two pin header
J2 Drive power connector
J3 three pin header, pins 2 and 3 shunted
J4 Outline / pads for two pin header
P1 IDE connector (pin 20 snipped)
U2 F245 Logic

Note the much reduced chip count.

ARCO in a 8550

From Peter:
   Some versions of the ARCO IDE had been designed to substitute the "HD Riser" card in the hidden 4th slot on the Mod. 50. You just remove the blue tab at the card front and remove the rear slotcover - and  the card should fit in there.

IDE in an IML Machine?

Well, sort of. The IDE controller can only be installed in a non-IML machine, such as the 8580, or a 90/95/85 with Flash BIOS. If you have a Type 1 upgrade DX2-66 complex OR a Type 4 complex, OR a 9585 then you can use this controller and IDE drives. I installed an AC-1075 and hooked up a WD-AC2420 drive in my 9590-OPT...

System Partition on IDE?

Yes and no. Yes it will install a system partition, BUT it will be a 3MB primary partition. You can install an extended partition, but you still cannot access the system partition the drive laid down (shades of the IBM Fast SCSI-2). Of course, the AC1075 does not use the Int4b interface required by IML systems...

Start Up Sequence

Make sure you select A: then Hard Drive 0 in startup sequence if you want to boot from the IDE drive. If you have a SCSI controller, you can have a SCSI drive selected as the boot device.

AC-1075 with IBM SCSI Adapters under W95

Although the startup sequence functions just fine selecting either the IDE drive or the SCSI drive for a start up device, W95 bombs when you try to look at hardware performance. There is no provision in the ARCO adf to change the AC-1070's IRQ from 14. And everyone knows that the IBM SCSI adapters only have IRQ 14 support. Though the two IO ranges are separate (ARCO in the 200s, IBM in the 300s) W95 can't handle the shared IRQs.

W95 and the AC-1070

From a snippet- (Looks as if Win95 does not recognize the ARCO as valid IDE controller ... control panel does not even show the HD). 

More to come. I must get my 9590 back up to install W95 on an IDE drive.... 

BIOS Capabilities

Version E (BIOS EPROM ver 3.03) supports 2Gb hard disk on PS/2 70; but version C (BIOS EPROM ver. 3.00) only supports 540 meg (525 Mb) hard disk in the same system.

CD-ROM Drives on ARCO 1070

William Walsh was cracking the whip down at, and came up with:  Note: The wildman did not have the ARCO CD-ROM drivers!

Decided to try my ATAPI CD-ROMs with the ARCO 1070 controller. According to the startup screen, the controller has ROM Version 3.05. I was doing this in a Model 50Z PS/2. I also tried all of this in a 9577 Bermuda, an 8557slc, and a Model 8570-E61.

The first thing I learned from trying this is that there must be a hard disk attached to the adapter as well. I couldn't seem to get it to find any of my CD-ROM drives without a hard disk attached. The ADF and Set Configuration screens kind of hint at are allowed to pick a type of IDE device for the slave device only. There is no similar option for the master device.

Next thing I learned is that you have to use an external power supply for any CD-ROM drive above 6X with your Model 50. (The 70 PSU seemed to handle things OK.) The 50Z PSU simply couldn't stand the 8X and higher drives, even with no other adapters in the machine. I sort of expected this, seeing as it is a small supply.

The ARCO adapter also seems to be picky about what kind of CD-ROM drives it will accept. I had no problems with all of my 4X or 6X drives (all NEC units, and one Torisan), and of the one 24X drive (Toshiba) I tried, it was found by the adapter as well. I did not have the same luck with any of my 8X Hitachi drives. Those drives (8X Hitachi) resulted in system lockups and hard disk (10xxx) errors during POST.

Anyway, once I had a CD-ROM drive installed and recognized by the adapter, I tried loading DOS device drivers for the CD-ROM drive. The first driver I tried (a seemingly universal one) just locked the machine whenever it loaded. No text, no errors, nothing at all. Just a lockup. I tried other drives with that, and when I was finally satisfied that it was not the drives, I tried another universal IDE CD-ROM device driver. It loaded, but found no drives, no matter what.

It seems that the unusual I/O addresses of the ARCO adapter throw the CD-ROM device drivers that I tried for a loop.

Summary: In theory, it seems that BIOS revision 3.05 of the ARCO card will support certain CD-ROM drives, but that the device drivers I tried to use to make these CD-ROM drives work either locked the computer or could find no CD-ROM drives.

It looks as though if someone wanted to use this adapter for a CD-ROM drive, they would have to write their own device drivers for's a shame that I don't know how to do that...I would if I could...

PIO Mode Only?

Note: From the User's manual: "... the ARCO BIOS allows the AC-1070/75 to run at I/O addresses 2510h or 2520h as well as respond to interrupt 14".

>The .ADF for the ARCO makes NO reference to the IRQ used (if any). Now this could mean that it's hard-wired to IRQ14 (as is the onboard ESDI), or that it is I/O polled.

From Peter:
   It seems to be used in PIO mode. If it were using any IRQ it should have the INT mentioned under "fixedressources" as have the IBM MCA SCSI controllers like in the below example:

  int 0eh

The ARCO also uses 16 I/O addresses on 2510h to 251Fh (alternatively: 2520h - 252Fh), which is pretty unfamiliar. Usually the IDE adapters uses 8 I/O ports in the 1F0h - 1F7h (170h - 177h secondary) as data-port and 3F6h (376h secondary) as control-/ status port. And IRQ 0Eh (0Fh) as interrupt.

So the ARCO is anything but not a standard IDE-controller anyway. I  think it is best used under DOS/Win3.x or (probably) OS/2 ... not recommended for Win95 / 98 / NT - as usual.

The ROM-BIOS -by the way- can be set to disabled in the Setup.

Max Drive Size

The ARCO may not see the 2.5 (doubtful) It does have an EIDE limit of 2.1GB accordingly and also supports internal EIDE CD-ROMs (for 5.25" bay units). But it has its own Drive table settings on the card. Most likely when you preformatted the drive on a different computer the CYLS/HDS/S-T are different than what the BIOS on the card is going to see.

The AC-1070 controller's adapter BIOS supports IDE drives up to 2 GB. If a drive was partitioned and formatted to a higher capacity, the controller will not permit the drive to operate under that partitioning scheme.

My question - will it allow multiple 2.1 GB partitions?


The @6263.adf, dated 07/02/95 has a section for CD-ROM support.


MCIDE.EXE shows you the configuration of any hard drive attached to an ARCO MCA hard drive adapter.  The program displays the drive information provided by the hard disk manufacturer, so it may not always be accurate.  MCIDE.EXE will also display the ARCO adapter information.


From Tim Clarke:
   Before this gets too out of hand - the rules for mixing an IDE/ESDI adapter with SCSI adapter(s) *for the Model 80* (and probably all others) are as follows:

  1. you may only install one IDE or ESDI adapter
  2. IDE/ESDI adapter's BIOS ROM *must* be configured with a lower address than that of the SCSI adapter(s)

This is because the IDE/ESDI BIOS ROM code isn't intelligent enough to "add" the drives that it supports after any drives which may have already been installed by another BIOS ROM (e.g. multiple SCSI adapters with multiple HDs each). It assumes that the drive(s) that it supports will always be Drive 0 (BIOS Drive 0x80) and Drive 1 (BIOS Drive 0x81). The IBM SCSI adapters' BIOS ROM is designed to "add" it's drives to a system which already has one or more HDs already "installed" and utilizes the XBDA (eXtended BIOS Data Area) to chain Int 13h, Int 4Bh (IBM SCSI) and note "first" and "count" values for each SCSI adapter.

Supposed Specs

Transfer rates in excess of 1200Kbps
On board BIOS for intelligent interface
Automatic Drive Recognition (ADR) recognizes / supports all IDE drives

AdapterID 6263 ARCO Computer Products, Inc (IDE Adapter)

Adapter Memory Location
   Select the ROM segment for the ARCO IDE adapter
      <"Segment DC00" (dc00-dfff)>, D800 (d800-dbff), D400 (d400-d7ff), D000 (d000-d3ff), CC00 (cc00-cfff), C800 (c800-cbff), ROM DISABLE

IO Address
   The Adapter  I/O address location is:
     <"2510-251F"(2510-251f)>, 2520-252F (2520-252f)

Slave Drive is
   Supports ATAPI device (CDROM) that is a slave drive
      <"ATA Device">, ATAPI Device, Not Installed

Content created and/or collected by:
Louis F. Ohland, Peter H. Wendt, David L. Beem, William R. Walsh, Tatsuo Sunagawa, Tomáš Slavotínek, Jim Shorney, Tim N. Clarke, Kevin Bowling, and many others.

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