В том-то и дело, что существуют. APIC-модуль нужен

В том-то и дело, что существуют. APIC-модуль нужен в составе проца.
Кроме того учти - все эти мамы ("Gygabite GA586DX" и "GA5DX" - хорошие примеры) без AGP и большинство не рассчитано даже на "Р55С" (только на "54"). Чтобы не углублятся в писанину, привожу FAQ для одной из самых продвинутых мамаш на "НХ" :

Does it Support Cyrix Processors?
Yes, the Tomcat series supports Cyrix Processors. The CPUs supported on the Tomcat boards are the P120+, P150+, and the P166+. The P200+ CPUs are not supported. Tyan does not currently support the 75 MHz bus rate on any of our models or the openApic SMP standard. Please contact Cyrix for more information.

Does the motherboard support MMX?
Yes. The Tomcat III series will support MMX with a BIOS upgrade. Tomcat I and IIs will be able to use the MMX Overdrive, the Tomcat III will work with 166MHz MMX CPUs in dual mode and 200MHz MMX CPUs in single mode only. Only the Tomcat III series supports 2.xx voltage settings for the standard MMX processor. DUAL MMXs are not officially supported past 166MHz. The Tomcat IV will support the entire range of Intel MMX CPUs up to 233MHz View the CPU Compatibility Chart for the latest news.

What's the advantage of Dual Intel Processors?
The advantage of Dual processors can only be seen when using a SMP compliant operating system such as Windows NT. 80% efficiency of the second CPU is generally the amount of additional computing power you will receive when upgrading to a second CPU. This will depend greatly on the software you are using and the operating system. Areas of interest for dual processing would be CAD and 3D animation with software like 3D Studio MAX and Adobe Photoshop.

What operating systems support multiprocessing?
Windows NT, SCO Unix and others support multiprocessing. Check with your software vendor for more information.

Can I use a single CPU on the Dual board then upgrade to two later?
Certainly. The only requirement/recommendation is that you get the same version of the CPU you currently own. Please note that Cyrix does not support dual processing. Contact Intel for more information about S-Spec numbers and compatibility issues with an existing CPU.

Do the two CPUs have to be the same?
Yes. The CPUs must be the same speed and manufacturer with the exception of the CYRIX CPUs which do not support dual processing. The Tomcat IID and IIID only support CYRIX CPUs in single CPU mode only.

1.6 Is the main RAM memory shared between the two CPUs?

Yes. Each CPU does not have it's own bank of memory. All system memory is shared between the two CPUs.

1.7 Is the main CACHE memory shared between the two CPUs?
Yes. Each CPU does not control a separate cache module. The total system cache (L2) is shared between the two CPUs.

What Burst module is recommended for this system board?
With the release of the Intel HX chip set, Intel has changed the COAST Module specification. Although the modules and connectors still physically look the same, Intel has changed the signal for two pins. Be sure to use cache modules that support the Intel HX chipset. Older modules omit these two signals and can cause the system to not boot up from the floppy or hard disk drive. The following is a list of certified modules that have been tested to work with the Tomcat. Our part number for the 256K and 512K burst modules are stated below:

256K Module S1543-PB256
512K Module S1543-PB512A

Be certain that you specify this part number to be used with your specific motherboard. Be aware that the Titan III module will NOT work in the Tomcat series. Consult your dealer for ordering and pricing information.

Why does Windows 95 show that I have onboard IDE or a PS/2 mouse when I disabled it in the BIOS?
When Windows 95 scans your hardware, it finds the chipset which supports onboard IDE or an onboard PS/2 mouse. Regardless of the BIOS settings, Windows 95 will always see these options.

Does this board support USB?
Yes. The Tomcat series will have the USB built onto the board however, earlier versions of the Tomcats have the USB pins on them although the feature is disabled in the chipset. The boards without USB support are the Tomcat I and II boards without a U in their part numbers. Users may purchase a USB PCI card from CMD and Tyan when they become available. If you wish to contact CMD, their web page is cmd.com Check with your vendor about USB support on boards they have in stock. Motherboards with the I82371SB chip with revision SU093 fully supports onboard USB. All Tomcat III series boards are shipped in this configuration. USB Cables are sold separately through your favorite distributor or dealer.

Why can't I get SMP (dual processor mode) to work in NT?
The most common problem is an incompatibility with the SMP HAL shipped with Windows NT versions prior to 3.51 and the motherboard's chipset. If you are upgrading from an older version of NT prior to 3.51, first install the NT as a standard PC (single processor kernel). After installation of the older version of NT, install NT 3.51 using the default multi-processor kernel it provides. NT will not recognize your dual CPUs if you do a 3.51 upgrade. Always use the Custom install feature. For more information and specific error messages, please contact Microsoft for more O/S support.

What's the difference between the Tomcat I, II, III, and IV?
The two boards are identical except for the fact that the Tomcat I has only 1 CPU socket where the Tomcat II has 2 CPU sockets. The performance is identical when running in single CPU mode. The Tomcat III is identical to the Tomcat I and II with the exception that the IIIs have soldered on cache which is not upgradeable. the Tomcat IIID supports 512K onboard cache only while the IIIS support 256K or 512K onboard cache which must be ordered at time of purchase. Cache is not upgradeable on the Tomcat III series. The Tomcat IV uses split rail voltage regulators which will support a greater range of CPUs. Consult the CPU Compatibility chart for complete details.

What's the story about the 512K coast module and the Tomcat II?
We originally qualified a working Coast module from a supplier but were not informed that a few components had changed. Because of this, a small number of cache modules were not qualified. The Tomcat I was not affected. Consult your dealer for more information.

Where can I find J60-65 for MMX Voltage Jumpers?
There is a misprint on the jumper settings in the manual however, the chart is correct. Please disregard mention of J60-65. J60-62 should read as J37-39 and J63-65 should read as J42-44.

Will the Tomcat Series Support 75 MHz and greater bus speeds?
No. There are no upgrade plans to incorporate these bus speeds.

What's the cacheable range on the Tomcat series?
The Tomcat I and II are shipped standard with a cacheable range of 64MB. In order to cache more than 64MB of ram on the Tomcat I and II, you need to purchase a 32Kx8 Tagram module which is available from your reseller or local computer dealer. The Tomcat III series motherboard ships standard with a cacheable range of 512MB. There is no need to upgrade the tag ram module as it is pre-soldered to the motherboard.

Where's J8?
J8 is located between the IDE connector and the simm sockets. Because of a hole in the motherboard at that location, the silk screening may read as J3.

Can I run dual AMD CPU