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The 286's internal registers (2022)

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Re: The 286's internal registers (2022)

#11

Post by andrewf »

qingcharles wrote: post #7

Were the segment registers (fs, gs) slower than the general registers (ax, dx)? I used to use them all the time as temp variables :/

From the file linked in https://www.vogons.org/viewtopic.php?p=534845#p534845, it looks like 'mov fs, ax' may have been 5 cycles compared to 3 for 'mov dx, ax', with no penalty in the other direction? So probably net faster than using memory instead.

But +15 cycles if you're in protected mode. In this case I think you'd also cause a fault by storing values into a segment register which weren't valid indexes into the LDT/GDT.

Re: The 286's internal registers (2022)

#12

Post by dholm »

j4nvo wrote: post #10

My first computer was a 386. There was a reference program I used all the time and I can’t remember it for the life of me. It was menu driven and had a ton of information on hardware, including CPU’s, UARTS, registers and their uses, interrupts etc. Sounds vague I know, but does anyone have any idea what that program was called?

Could it have been Dr. Hardware Sysinfo?

https://www.dr-hardware.com/pghgretro.htm

Re: The 286's internal registers (2022)

#13

Post by kjs3 »

qingcharles wrote: post #9
YZF wrote: post #5

Earlier quoted context omitted.

Sounds like you live in a computer museum ;) How did you end up owning these? I kept a handful of older computers, my ZX-81 still sitting somewhere, ZX-Spectrum, Apple Newton. My HP-48GX is used by my daughter. I have a dual CPU 486 machine... I doubt any of these is worth any $'s ...

I think Linux dropped support for 486, right? That was the only thing I remember that supported dual 486.

NCR had a couple of SMP 486 boxen (NCR 3450, 3550 & 3600) that were supported by SCO Unix, SVR4 and (early) NT. I think they had support for OS/2. ALR, Unisys and Compaq made somewhat similar 486s with roughly similar OS support (although I vaguely recall the Unisys stuff was OEMed elseware). The support problem was 486 predated standardized SMP hardware (APIC), so it was all custom hardware.

Re: The 286's internal registers (2022)

#14

Post by justsomehnguy »

YZF wrote: post #5
johnklos wrote: post #4

Earlier quoted context omitted.

I did something in between - I kept the physically small systems (Landisk, VAXstation VLC, Mac LC III+, Mac Quadra 610, Cobalt Raq, EdgeRouter, various Pis, et cetera) and some of the more useful larger ones (Amiga 4000, VAXstation 4000/60 and 4000/90, AlphaServer DS25), and I put them to use building NetBSD pkgsrc packages so they're useful. Considering the fact that I paid less than $100 for the VAXstation 4000/60,…

Sounds like you live in a computer museum ;) How did you end up owning these? I kept a handful of older computers, my ZX-81 still sitting somewhere, ZX-Spectrum, Apple Newton. My HP-48GX is used by my daughter. I have a dual CPU 486 machine... I doubt any of these is worth any $'s ...

> I doubt any of these is worth any $'s ...

as always with a legacy $anything the price is for those who really want it.

I have Psion 3 (with a damaged screen cablr, but with a whopping 1MB SSD), it costs nothing, but people selling the working ones for more than $100

Re: The 286's internal registers (2022)

#15

Post by johnklos »

YZF wrote: post #5
johnklos wrote: post #4

Earlier quoted context omitted.

I did something in between - I kept the physically small systems (Landisk, VAXstation VLC, Mac LC III+, Mac Quadra 610, Cobalt Raq, EdgeRouter, various Pis, et cetera) and some of the more useful larger ones (Amiga 4000, VAXstation 4000/60 and 4000/90, AlphaServer DS25), and I put them to use building NetBSD pkgsrc packages so they're useful. Considering the fact that I paid less than $100 for the VAXstation 4000/60,…

Sounds like you live in a computer museum ;) How did you end up owning these? I kept a handful of older computers, my ZX-81 still sitting somewhere, ZX-Spectrum, Apple Newton. My HP-48GX is used by my daughter. I have a dual CPU 486 machine... I doubt any of these is worth any $'s ...

I've always had an appreciation for odd hardware, and I've just tried to keep what I like of what I have.

Big fan of the Sinclairs - small, simple, yet filled with all sorts of neat tricks that made them inexpensive and simple. That cleverness makes for a great set of lessons to modern computer programmers and architects.

Re: The 286's internal registers (2022)

#16

Post by qingcharles »

andrewf wrote: post #11
qingcharles wrote: post #7

Were the segment registers (fs, gs) slower than the general registers (ax, dx)? I used to use them all the time as temp variables :/

From the file linked in https://www.vogons.org/viewtopic.php?p=534845#p534845 , it looks like 'mov fs, ax' may have been 5 cycles compared to 3 for 'mov dx, ax', with no penalty in the other direction? So probably net faster than using memory instead. But +15 cycles if you're in protected mode. In this case I think you'd also cause a fault by storing values into a segment register which weren't valid indexes into the…

Thank you!

Re: The 286's internal registers (2022)

#17

Post by muziq »

YZF wrote: post #5
johnklos wrote: post #4

Earlier quoted context omitted.

I did something in between - I kept the physically small systems (Landisk, VAXstation VLC, Mac LC III+, Mac Quadra 610, Cobalt Raq, EdgeRouter, various Pis, et cetera) and some of the more useful larger ones (Amiga 4000, VAXstation 4000/60 and 4000/90, AlphaServer DS25), and I put them to use building NetBSD pkgsrc packages so they're useful. Considering the fact that I paid less than $100 for the VAXstation 4000/60,…

Sounds like you live in a computer museum ;) How did you end up owning these? I kept a handful of older computers, my ZX-81 still sitting somewhere, ZX-Spectrum, Apple Newton. My HP-48GX is used by my daughter. I have a dual CPU 486 machine... I doubt any of these is worth any $'s ...

A dual 486 is a very special beast.. What motherboard is that

Re: The 286's internal registers (2022)

#18

Post by YZF »

muziq wrote: post #17
YZF wrote: post #5

Earlier quoted context omitted.

Sounds like you live in a computer museum ;) How did you end up owning these? I kept a handful of older computers, my ZX-81 still sitting somewhere, ZX-Spectrum, Apple Newton. My HP-48GX is used by my daughter. I have a dual CPU 486 machine... I doubt any of these is worth any $'s ...

A dual 486 is a very special beast.. What motherboard is that

tbh not sure. I'd have to dig it out of the crawlspace and have a look. But yeah, seems like those indeed are rare. Had no idea and I guess some chance I'm misremembering and it's a Pentium or something.
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