MCA Port

This page is related to a port of ReactOS that only exists as an idea ReactOS does not support this platform, nor is being ported to it. You are free to start working on porting it, but don't forget to announce it publicly in the chat or in the development mailing list.

MicroChannel Architecture is a proprietary bus that was supposed to supersede the ISA bus, however it was itself subsequently superseded by the PCI bus architecture. It was primarily used in the IBM Personal System/2 computer series.

Status

ReactOS is not ported to MCA-based machines yet.

IBM PS/2 Server 95 and Server 95A series use Pentium CPUs so they could run ReactOS once it's ported. Also it's known some of Model 90 and 95 series are upgradable with Pentiums.

Existing work

• Initial support for Advanced BIOS: ABIOS grep, ABIOS commits

Hardware

Most known MCA-based machines were IBM PS/2, however there were also other ones. We will focus mainly on IBM PS/2 hardware here.

Last models in the series are unique for the fact the CPU resides on a complex card that can be swapped out with some complexes sporting a completely different architecture (ranging from a 386, 486, to Pentiums both in Socket 4 and Socket 5). MMX can be achieved by using an Overdrive in a Socket 5. These systems can hold up to 256 MB of RAM that's fully cacheable thanks to the discreet chips on the complex card: using a rather expensive Intel-designed memory controller.

They have 2.88 MB floppy disk drives installed. However, you will still need 1.44 diskettes for the reference diskette, diagnostics diskette, and any boot diskettes to initiate booting into the CD-ROM drive. Booting from CD-ROM is usually not supported, however it depends on the SCSI controller firmware. For the HDD there are two options: either an ESDI adapter or SCSI controller. For input there are standard PS/2 connectors for keyboard and mouse.

Conventional PS/2 machines are not supporting ISA or PCI buses, they only have MCA bus, so a new HAL has to be created. The BIOS looks very similar to the Standard PC BIOS, and even seems to use standard MBR scheme for booting, however for the initial system configuration (or hardware reconfiguration, including setting up the system date and time) you will always need to boot from a reference floppy disk.

In Windows NT 4.0 (and Windows 2000 Beta builds) there were several HALs for this architecture:

File Name	Hardware ID String	HAL Name
halcbusm.dll	cbusmc_mp	Corollary C-bus MicroChannel Architecture MP HAL Version 3.4.0
halmca.dll	mca_up	PC Compatible MicroChannel HAL
halmpsm.dll	mps_mca_mp	MPS 1.4 MCA - APIC platform

During the 1st stage setup halmca.dll is used in all 3 cases, according to [Hal.Load] section of the TXTSETUP.SIF file.

Emulation

• 86Box (as of version 3.7.1) emulates several PS/2 models like Model 50, 60, 70 type 3, 80 type 2/3, but does not emulate Pentium-based models yet.

See Also

• IBM PS/2 - Wikipedia
• List of IBM PS/2 models - Wikipedia
• Micro Channel architecture - Wikipedia
• Personal System/2 Model 95 Information and Software - System Type: 9595
• IBM PS/2 (Enhanced Model 95 XP 486)/PC Server 95 - Technical specifications
• IBM - ADF-File Library - Adapter Description Files
• Kingston 64MB Memory Expansion Adapter - ADF and initialization files, emulated by 86Box
• Windows 2000 Beta build 1877 running on PS/2 machine - emulated by 86Box
• NetBSD 9.1 booting on a PS/2 with 9553/8555 Reply TurboBoard - tweet by Andrei Warkentin