https://ardent-tool.com/docs/pdf/PS2_Model_25_Technical_Reference_Jun87.pdf

Shared Interrupt Hardware page 28 physical

Interrupt Sharing
A standardized hardware design concept has been established to enable
multiple adapters to share an interrupt level. The integrated adapters
do not use interrupt sharing.

Folks wonder why IBM brought out the low end 8525 and 8530...

If the 25 / 30 were significantly more reliable than the large horde of
clones, perhaps that was a big reason to offer them to the business
community...

Methinks IBM sunk quite a bit into refining an ISA based system,
providing standards. Clone systems might not be made with consistent bus
and adapter standards.

Huh...

On 7/10/2021 09:29, Louis Ohland wrote:
>
> https://ardent-tool.com/docs/pdf/PS2_Model_25_Technical_Reference_Jun87.pdf
>
> Shared Interrupt Hardware page 28 physical
>
> Interrupt Sharing
> A standardized hardware design concept has been established to enable
> multiple adapters to share an interrupt level. The integrated adapters
> do not use interrupt sharing.

After further reflection, I'd think that IBM reviewed the ISA bus. Not
so much to design it, but to re-establish timing and signal tolerances.
They most likely corrected a few issues, made the system better suited
for automated assembly, and did their best to reduce service calls /
warranty action... Just like the rest of the PS/2s...

On 7/10/2021 11:11, Louis Ohland wrote:
> Folks wonder why IBM brought out the low end 8525 and 8530...
>
> If the 25 / 30 were significantly more reliable than the large horde of
> clones, perhaps that was a big reason to offer them to the business
> community...
>
> Methinks IBM sunk quite a bit into refining an ISA based system,
> providing standards. Clone systems might not be made with consistent bus
> and adapter standards.
>
> Huh...
>
> On 7/10/2021 09:29, Louis Ohland wrote:
>>
>> https://ardent-tool.com/docs/pdf/PS2_Model_25_Technical_Reference_Jun87.pdf
>>
>>
>> Shared Interrupt Hardware page 28 physical
>>
>> Interrupt Sharing
>> A standardized hardware design concept has been established to enable
>> multiple adapters to share an interrupt level. The integrated adapters
>> do not use interrupt sharing.
>

One further thing I forgot... there once was a company that made some
upper-end ADP stuff, printers? They had a reasonably performing product,
but they announced a much better version "next year". So folks put off
buying the initial product, cutting the revenue flow. Then the super
whizz-bang was delayed, and sales never recovered.

Perhaps IBM wandted to avoid that, and came out with a initial product
that was competitive [based on ALL features] and waited to get the
successor ready before dropping it on the public.

Road to hell is paved with good intentions...

On 7/10/2021 13:32, Louis Ohland wrote:
> After further reflection, I'd think that IBM reviewed the ISA bus. Not
> so much to design it, but to re-establish timing and signal tolerances.
> They most likely corrected a few issues, made the system better suited
> for automated assembly, and did their best to reduce service calls /
> warranty action... Just like the rest of the PS/2s...
>
>
>
> On 7/10/2021 11:11, Louis Ohland wrote:
>> Folks wonder why IBM brought out the low end 8525 and 8530...
>>
>> If the 25 / 30 were significantly more reliable than the large horde
>> of clones, perhaps that was a big reason to offer them to the business
>> community...
>>
>> Methinks IBM sunk quite a bit into refining an ISA based system,
>> providing standards. Clone systems might not be made with consistent
>> bus and adapter standards.
>>
>> Huh...
>>
>> On 7/10/2021 09:29, Louis Ohland wrote:
>>>
>>> https://ardent-tool.com/docs/pdf/PS2_Model_25_Technical_Reference_Jun87.pdf
>>>
>>>
>>> Shared Interrupt Hardware page 28 physical
>>>
>>> Interrupt Sharing
>>> A standardized hardware design concept has been established to enable
>>> multiple adapters to share an interrupt level. The integrated
>>> adapters do not use interrupt sharing.
>>
>

Note that the Model 30 was first - and the Model 25 planar is the same functionality made later (ok, the Model 30 has 128Kb soldered on the planar, and the Model 25 has DIP sockets for the 128Kb "upgrade" (from 512Kb to 640Kb) that is almost always present anyway). And my theory is that IBM had Seiko-Epson designed the Model 30 - they made the entire chipset for it. To wit, the Epson Equity 1e is a Model 30 clone down to MCGA video and 720Kb diskette drives.

The Model 30 was an IBM replacement for the XT - notably the deployed 5250 and 3270 emulations that were still big for them. The last of the Model 25 systems were only sold in a school environment and morphed into the larger EduQuests. But they were based on the 8086, which was ten years old at the time of the initial PS/2 release - and the attempts to morph them into the "Executive" and "Clinical Workstation" didn't do so well.

Ripping, page construction should happen today...

Further pondering... Quite possumble that the ISA systems were cash
cows. Most engineering was in existence. IBM tightened up the ISA bus,
updated the design with greater integration [possumble bleed-over from
MCA development], brought the BIOS into PS/2 compliance, and increased
ease of assembly.

The PS/2s at the lower end could be considered as mules. Slow, sure
footed, and cheaper than thoroughbred race horses. Remember the
customers - businesses. Down time cost actual money.

On Mon, 12 Jul 2021 10:41:32 -0500, Louis Ohland <ohland@charter.net>
wrote:

>Further pondering... Quite possumble that the ISA systems were cash
>cows. Most engineering was in existence. IBM tightened up the ISA bus,
>updated the design with greater integration [possumble bleed-over from
>MCA development], brought the BIOS into PS/2 compliance, and increased
>ease of assembly.
>
>The PS/2s at the lower end could be considered as mules. Slow, sure
>footed, and cheaper than thoroughbred race horses. Remember the
>customers - businesses. Down time cost actual money.
>

It was just an attempt to cling to a market that was rapidly slipping
away. The Aptivas (and similar lines) that came next were all industry
standard parts.