Mungo wrote on 2023-11-19, 12:10:

I haven't benchmarked 8 Mhz 8086 vs. 10 MHz 8088. How close are their speeds in practice?

I haven't benchmarked them either.
But I expect the difference 8088 vs. 8086 to be similar to V20 vs. V30 - Re: Adventures of a generic Turbo XT clone [updated original post with pics]

"The IBM PC had the memory throughput of an Atari 2600."
Source: https://retrocomputing.stackexchange.com/ques … -pc-to-4-77-mhz

PS: I've deleted my previous posting. It was too long and probably of no real use, except of angering some people.
I'll leave the quote, I've posted earlier, though, but without my personal opinion.
The link is about questions why the IBM PC had certain limitations.

Jo22 wrote on 2023-11-19, 23:04:

"The IBM PC had the memory throughput of an Atari 2600." Source: https://retrocomputing.stackexchange.com/ques … -pc-to-4-77-mhz […]
Show full quote

"The IBM PC had the memory throughput of an Atari 2600."
Source: https://retrocomputing.stackexchange.com/ques … -pc-to-4-77-mhz

PS: I've deleted my previous posting. It was too long and probably of no real use, except of angering some people.
I'll leave the quote, I've posted earlier, though, but without my personal opinion.
The link is about questions why the IBM PC had certain limitations.

The article ignores that there were 5,6 and 8mhz clockings of the 8088, some old IBMs ended up with -6 parts oddly

Did quite a bit of performance investigation around 8088/8086 hardware. The topic is very interesting to me.
My signature points to a dictionary. The first few links there contain data related to the subject.
Intention was to broaden a bit the information spectrum since it is very narrow given the class of the hardware and its age.

Hope to be able to add 1-2 more boards for completeness at some point later - the Juko NEST 8086 and another assembly based on Faraday chipset.
Anyhow, figured i should drop a line here for what it is.

So if 16bit bus makes the computer about 50-60 % faster, then that would mean that 10 MHz 8088 compares to about 6.5 MHz 8086?

rmay635703 wrote on 2023-11-20, 02:35:

Jo22 wrote on 2023-11-19, 23:04:

"The IBM PC had the memory throughput of an Atari 2600." Source: https://retrocomputing.stackexchange.com/ques … -pc-to-4-77-mhz […]
Show full quote

"The IBM PC had the memory throughput of an Atari 2600."
Source: https://retrocomputing.stackexchange.com/ques … -pc-to-4-77-mhz

PS: I've deleted my previous posting. It was too long and probably of no real use, except of angering some people.
I'll leave the quote, I've posted earlier, though, but without my personal opinion.
The link is about questions why the IBM PC had certain limitations.

The article ignores that there were 5,6 and 8mhz clockings of the 8088, some old IBMs ended up with -6 parts oddly

The odd part might come down to original 808x clock timing requirements, it needed an asymmetric clock timing pulse with particular rise times, like ___/"\___/"\___/"\__ kinda thing, so driving it off a simple 50:50 mark space oscillator, or not "conditioning" the rising edge of the pulses exactly to it's liking, tended to mean you needed to use a faster part than indicated by nominal clock frequency for the best stability. See original data sheets to appreciate the full weirdness of it.

Thank you, that's interesting! 🙂👍

From what I remember (vaguely) the NEC V20/30 had a different duty cycle, too.
So strictly speaking, it was running a little bit out of spec when installed on PC/XT motherboards (as an plug in replacement).

Edit: I can be wrong, but I think that intel clock generator IC was used on PC motherboard.
So dividing that 14 MHz* clock wasn't absolutely needed to get correct timings for the 808x, the intel IC could have been taking care of proper 808x timings if a different clock was used.

(* to my understanding, the ~14 MHz frequency was traditionally convenient, because a fraction of it can be used for the, um, "recovery" cycles of processors.
It had to do with most things somehow being tied to NTSC colour burst frequency of 3,57 MHz (~14 MHz is a multiple).
A few rare systems from Europe used 4,4 MHz, the PAL equivalent.)

Jo22 wrote on 2023-11-23, 15:52:

From what I remember (vaguely) the NEC V20/30 had a different duty cycle, too.
So strictly speaking, it was running a little bit out of spec when installed on PC/XT motherboards (as an plug in replacement).

No.
8088/8086 need 33% duty cycle.
V20/V30 support both 33% and 50%.

And of course, the most obvious way to produce 33% duty cycle is dividing the XTAL frequency by 3.

Grzyb wrote on 2023-11-23, 23:29:

No. 8088/8086 need 33% duty cycle. V20/V30 support both 33% and 50%. […]
Show full quote

Jo22 wrote on 2023-11-23, 15:52:

From what I remember (vaguely) the NEC V20/30 had a different duty cycle, too.
So strictly speaking, it was running a little bit out of spec when installed on PC/XT motherboards (as an plug in replacement).

No.
8088/8086 need 33% duty cycle.
V20/V30 support both 33% and 50%.

And of course, the most obvious way to produce 33% duty cycle is dividing the XTAL frequency by 3.

No. 50% is official. 33% works, but is not in spec.
According to this document, at least.

https://datasheet.octopart.com/UPD71011C-NEC- … heet-106570.pdf

Jo22 wrote on 2023-11-24, 05:21:

https://datasheet.octopart.com/UPD71011C-NEC- … heet-106570.pdf

Nothing about V20/V30 requirements there...

But - https://www.alldatasheet.com/datasheet-pdf/pd … C/UPD70108.html

Duty cycle would be tKKH/tCYK, right?

So, the minimum duty cycles - at the nominal CLK frequency - are:
- for the -5: 69/200 = 34.5%
- for the -8: 44/125 = 35.2%
- for the -10: 39/100 = 39%

Really?
V20 isn't a drop-in replacement for 8088, after all???

Edit:

Grzyb wrote on 2023-11-24, 05:59:

Jo22 wrote on 2023-11-24, 05:21:

https://datasheet.octopart.com/UPD71011C-NEC- … heet-106570.pdf

Nothing about V20/V30 requirements there...

Right. It's merely NEC's official V20/30 clock generator that features an 50% duty cycle.

Grzyb wrote on 2023-11-24, 05:59:

Really?
V20 isn't a drop-in replacement for 8088, after all???

I've never questioned that.
I merely said it's running a bit out of specification here (most things have quite some tolerances). 🤷‍♂️
Wikipedia mentions that 50% duty cycle, too.

Edit: Just double-checked.
The Olivetti M24 might need a modification, not sure.
Perhaps it will also run as is with a V30. 🤷‍♂️ M24 users may can answer that.

"The 5 MHz version of the processor can be used directly instead of the 8086.
In systems clocked at 8 megahertz, such as the Olivetti M24, the clock generator
and the crystal that determines the system clock may also need to be replaced because,
according to the specification, the V30 requires 50 percent instead of 30 percent duty cycle." (Machine translation)

Original article (1985): https://www.computerwoche.de/a/ibm-pc-tuning-von-nec,1171157

Englisch Translation

OK, note to self to examine every V20/V30 board I encounter, to see what's the duty cycle (same as CPU clock / XTAL frequency ratio, right?), and whether the CPU is underclocked.

Just noticed something.
None of the Sharp MZ series computers used an i8088.
They all used full versions of the processors, be it Z80, i8086 or iAPX 286.

https://en.wikipedia.org/wiki/Sharp_MZ

That's what I meant to say, the i8088 was sort of a mistake (technically, not economically). But it wasn't the only one.

The i8080 and i8085 are inferior to the Z80 and Z80 compatibles/derivatives/supersets.
That's why the Intel developers who worked on the 8080 had founded Zilog and created the Z80, the processor the 8080 originally was meant to be.

Edit: That's why I believe that the NEC V20 was the best that ever happened to the IBM PC.
It compares to the 8088 like an Z80 compares to the i8080.

Both the Z80 and NEC V20 are much more elegant/intelligent in their design than the predecessors.
The V20/V30 even have the ability to replace the 8080 in its functionality (8080 mode).

Edit: I forgot to mention, some of the 16-Bit MZ models ran MS-DOS, too.
There's even a video, albeit about an 80286 model.
https://www.youtube.com/watch?v=wPKchL5bKDw

Edit: Or let me put it this way, I wonder if the IBM PC was designed to be weak on purpose.

When the IBM PC 5150 was released, IBM did well with its mini computer businesses etc.

If the IBM PC was any more powerful than it was, say by using an 8086 or 68000, it would have been a threat to the other business fields.

Ok, maybe I'm just imagining things, but the development of Windows was similarly affected.

Both Windows 2.x and OS/2 1.1 shared same visuals.

Same was with Windows 3 and OS/2 1.2 and 1.3, with the difference that OS/2 had used the new GUI earlier.

So why was Windows 3.0 so crude/depressing looking in comparison to OS/2 at the time?
I think that was intentionally, due to pressure from IBM.

IBM was afraid of Windows stealing the show, so to say.
So Windows 3 was allowed to be an upgrade over Windows 2, but simultaneously had to be looking inferior to OS/2.

Then, after the split up, Windows 3.0 MME and Windows 3.1 was allowed to be looking much more friendly.

Edit: Okay, so how does all of this relate to the thread's topic?
Well, I just wonder if the IBM PC truly deserves to be considered a reference for how to build a good x86 PC.
It's a nostalgic and historical relevant piece of hardware, but was it ever "leading edge"?

Edit: I hope I'm not making people mad by thinking out loud here, but I believe without this question being answered, it's hard to think about designing an (new) 8086 PC.

Edit: I forgot to mention, I'm a young XT owner, too.

I have a Siemens Nixdorf M35 8810 PC with a very large, old mainboard and a Hitachi CRTC for its internal CGA..

I've upgraded it with a V20, a second graphics card (Hercules) and really love that old behemoth. ^^

So it's not that I hate XTs whatsoever.. It's just that I find it interesting to get rid of bottlenecks.

A new, all 16-Bit PC wouldn't loose its PC personality, whatsoever.
All the XT style components would still be there, software would still see an XT.

If done with care, the original IBM PC BIOS can run mostly on modified on same hardware (V20 patch needed, maybe).

CGA cards could still be used, too.
Even more, a new 16-Bit CGA card could be designed, but dual-ported RAM.

The timings of such a PC would be above original XT timings, of course.

But maybe a "Turbo Button" functionality could be implemented. Waistates, second xtal oscillator etc, not sure.