I think you can also run the NEC V30 (10mhz) in an XT 5160 if memory serves. I'm really not sure what else is out there that's more exotic.. certainly can't think of anything reaching 20mhz.

Pretty sure you have to swap the whole motherboard to one with a faster crystal though, I don't remember what boards people were getting.

I have a Juko ST clone board with an NEC V20 12 MHz CPU but, the manual indicates that a 15 MHz version was also available.
I know there was also an NEC V20HL that ran up to 16 MHz and I do seem to recall from my youth that there were one or two friends of mine that had some of these fast XT's.

I think 16 MHz was about the fastest XT (8088) based CPU's that was available but, I'm speaking under correction.
By the time those CPU's started to hit the market, you could probably buy a 286 or even 386SX for not much more.

PS: The NEC V30 has both a 16-bit internal & external data path. It won't work in an IBM PC XT.
It could be used as an upgrade path for something like your Olivetti M24 that did utilise the 8086 CPU.

^^ Juko is the name of the board, Super Turbo.. Unless I'm going senile, people were running V30s in those and dropping them in 5160s. That's a full computer upgrade though.

Or am I getting old and losing my mind? 😒

I'm just going off of memory, I'll assume I'm wrong 🤣, either way it doesn't go with the 8 bit cpu question so doesn't matter. I think the V20 was the fastest consumer upgrade option to drop right in an XT.

The Amstrad/Schneider PC1512 and PC1640 used an 8086, too! ^^
My father said he upgraded his 1512 with a NEC V30 way back in the 1980s.

8088 > V20
8086 > V30

8088 and 8086 are not pin compatible so you can't just drop 8086 in 8088 socket.

8086 is 16 bit internally

8088 is 8 bit internally

I'm pretty sure that 8088 is 8 bit externally - it has 8 bit data bus. Internally they are the same.

https://en.wikipedia.org/wiki/Intel_8088#Diff … s_from_the_8086

zyga64 wrote:

I'm pretty sure that 8088 is 8 bit externally - it has 8 bit data bus. Internally they are the same.

Correct. And that's why they are not pin-compatible. (should be self-explaining)

Olivetti Quaderno has 16MHz V30HL - according to speed tests, it was faster than a lot of 286s. Mine is unfortunately dead, but I recall running the speed tests years ago and I was impressed.

As far as I know 12MHz V20 was the fastest 808x on that desktop...but technically those systems were overclocked, so you couldn't really use an FPU or some speed sensitive ISA cards.

^^ interesting ... can you run a bus clock divider on 8088/86 or does the architecture just not support it?

I think it's probably possible to do a bus divider. There's no solution for the FPU as far as I know though. I believe there are actually circuits out there that allow you to double your CPU speed...so this way you could have a 20MHz CPU on a 10MHz board (but again no FPU).

8MHz V20 was common, and 10MHz were available (I think, or was this just overclocked 8MHz also?) but there were compatibility problems with some cards if you overclocked them to 12MHz.

I've never seen a 15MHz- I would assume even more compatibility problems than 12!

Maybe when equipped with a 15MHz CPU, the bus was decoupled. Are there any specific settings for the 15MHz version in the Juko ST manual?

I overclocked my Tandy 1000 SL with a NEC V30 to 9.54MHz and it scored 1195 dhrystones in checkit 3.0. My 12MHz V20 does 943.

A 16MHz V30 would score something like 2000 dhrystones and indeed it would beat some slower 286's.

A clock doubling circuit seems to be possible, i discussed this with James Pearce from lo tech some time ago. I don't know if V20/V30HL's overclock well, but running a V30 at 20MHz would be not only interesting but also quite the performance beasts. A 2500+ dhrystone XT would be absolutely crazy.

I recently overclocked my PC 5150 using the PC-SPRINT schematics. I'm using a crystal of 17.43 which gives me 5.81 Mhz on a NEC V20. I tried a 22.1Mhz (7.33mhz) but my memory is too slow (200ns). I will try with higher clocks (19mhz for example) once I get them in the mail...

Is the NEC V40 an 8088 clone or an 80286 clone?

It's not even really a clone of anything, it's an embedded V20 with some built-in I/O stuff; the closest match for an Intel CPU would be the 188 (but it's not pin-compatible with it).

harddrivespin wrote:

Is the NEC V40 an 8088 clone or an 80286 clone?

It's more like an 80186, I'd say.
Both share features found in microcontrollers.

However, judging by the instruction set, yes, it rather is like an 80286 clone. :)
In some way or another, the 80186 can be seen as an 80286 minus protected-mode and memory managment unit.

I really wonder which was designed first (8018x or 80286).
In the past, intel released CPUs prior microntrollers (8080 vs 8085).

Edit: @AlaricD Darn, you were replying faster than me, hah. ^^