The 486 test registers are described in the i486 Processor Programmer’s Reference Manual, starting on page 10-8. The 386 test registers are a subset.
Registers TR6 and TR7 provide access to the TLB. They are defined as follows:
The Am386 and Am486 were designed as clock-for-clock equivalents of the corresponding Intel CPUs, based on reverse-engineering and AMD’s previous second-source licenses — at least the Am386 even used the same micro-code as Intel’s 80386. The only speed advantages came from higher clock speeds (40MHz v. 33MHz) and, in some Am486 models, the use of write-back ...
Software can identify those early steppings on the 386 by checking whether the XBTS and/or IBTS instruction can be executed, since these instructions were dropped in later chip revisions.
Software must, however, first check whether the CPU is really an 80386 and not 486, because the some early steppings of the 486 temporarily re-used the opcodes of these two ...
I inquired about the CPU over on ee.se. The chip appears to be an AMD Am386DX-25.
Compare the lower printed number (107M7NX and 107M7NZ), the fonts used, the logo at the bottom-right, and the laser-etched number (23936).
Source: computerbase.de via @SpehroPefhany's answer on ee.se
@njuffa has pointed out that the logo laser-etched ...
Apart from the unrecognized branding on the CPU (ceramic; upper-right in photo) chip, this appears to be a bog standard ISA '386 motherboard, probably running at 25 MHz.
CPU looks like the right packaging for a 80386
Empty 80387 FPU socket
Quadtel "386" BIOS with appropriate late-80s Copyright
50.0MHz oscillator adjacent to CPU; usually provided ...
No, this sound card is definitely not intended for such a slot that expands the ISA slot to 32 bits.
This is a Compaq-specific sound card meant for a Compaq-specific ISA slot extension. There is no more than the six pins for Compaq-specific audio extensions.
Based on a few pictures of the card, it simply routes some audio signals between card and backplane. ...
Is it really so simple as just getting to higher clock speeds than Intel did?
Yes, it is that simple. Up and including the 486 AMD's CPUs were developed close to Intels devices, supported by in detail information provided by Intel as well as reverse engineering. AMD adapted the design to their production process. This included low level changes in how ...
Were those slots manufacturer-specific or was there some kind of (unofficial) standard?
(Well, there was EISA, but I guess it's safe to assume that this question is explicitly not about EISA)
What additional signals were available in these slots?
Most likely D16..31 and A24..31. Plus maybe BE0..3 - and that's where the main issue ...
Going by pinout and socket type it's a pretty generic 80386DX (*1) board based on the VIA FLEX I chipset (SL90xx). Probably 1990/91ish.
It would need a better set of photos - especially of the backside to find some hint. Finding the correct type without further marking is next to impossible, as many did produce following the same layout.
*1 - Visible due ...
You are getting everything wrong.
The 286 has integrated segmentation unit and protected modes to allow multitasking OSes and more memory (up to 16MB). It was actually used for that purpose in early versions of OS/2 and Windows.
The definition of "workstation" is arbitrary. 640kB DOS was becoming cramped, and the 286 allowed to use more memory.
It can be tested by performing various multiplication operations and verifying the result. List of such code that performs ten tests with various memory and register based operands is available for example at pcjs.org, but as others have already pointed out, the problem may only manifest under certain conditions and can depend on e.g. CPU supply voltage, so ...
If we want to talk about the formfactor and not necessarily have the device be called a tower, I would say the MacSE(1984) could make an interesting case study (pun intended). Although it could be argued it was more akin to the portables of its time but in a vertical orientation rather than a horizontal one. Portable/luggables still needed to be plugged into ...