8086 powered IBM PC compatible

need

I do remember 386 board with 8-bit CGA on it. while all of its bus is

Could you explain more about correctly accessing 8-bit bus in 16 bit ISA bus, particularly for 8086 processor. separate document or web site would be better I think.

Thanks

still

hmm , I would like the one with cassette port in it.

Lots of fun :-)

ed

we can obtain 16-bit wide SRAM today, does byte swapping still any use.

ld need

used

written

the

I believe 8088 is crippled version of 8086, with only 8-bit data bus

How come 8086 machine is faster than 80286 machine, was it clocked faster, which I doubt. Berlin wall is Kaput, could you share the NDA document with us now.

Danke Schoon

Do you mean the original five slot PC motherboard?

How about 8-bit or un-aligned accesses (I/O or memory)?

Architecturally, yes. Logically and physically, no. IIRC, the 8088 had a four-byte prefetch queue, while the 8086 had a six-byte prefetch queue. This difference was what was used to ID the particular processor.

The 80188 and 80186 were the same die (bond-out difference), however.

It wasn't. For the 8086 to be faster, it had to be a pretty horrid implementation of the '286 system. The '86 was a *lot* cheaper, however.

I have one of those PCs (and an EU w/10MB disk).

You are worse than SkyBuck.

There was one problem with the 80286, solved in the 80386 and beyond, that greatly slowed it down when using memory beyond the 20 address limit (in other words, the upper four address lines of the 80286 were non-zero.) [Obviously, this does NOT relate to the above discussion about the 8086 vs 80286, but it made me remember things so I'm writing it anyway. :P ]

The 80286 could not shift back from protected mode into real mode without a processor reset. So the BIOS routines that supported accessing memory past the 1Mb boundary would set up a protected mode environment, shift to protected mode, perform the indicated operation, and then ... well, then the BIOS used the clock calendar chip with a very tiny battery backed memory, stored a special code there so that on power reset it could look and realize that it was coming back from a protected mode call, and then would return to the caller in real mode rather than reboot the O/S from disk.

Which reminds me of yet another oddity. Anyone remember (I do) that code can be downloaded into a motherboard via the keyboard interface -- no disks required? A feature used to download diagnostic/test code for motherboard manufacturing.

Jon

still

I think that I still have a couple complete units, but I haven't looked at the pile of PC/XT stuff in 10 years.

In the beginning, 8086s _were_ faster than 286s because the 286 had a real MMU and the address translation took time, cycle-wise. Also, 8086s were available at 10 and 12 MHz from Siemens and other 2nd sources, while initial 286 clock rates were 6 and 8 MHz. (guess what IBM choose)

In addition, the first board designs did not use the address pipelining feature of the 286.

But then I had an ALR Fastboard-286 that reliably ran at 10 MHz with an overclocked Intel sample processor. The ALR was one of the first "good ones". It even ran "Interactive Unix". I tried to compile Berkeley spice 2G6 on it, still the Fortran version, and it was a fiasco with the large memory model. I also had to patch the disk descriptor tables in the BIOS to make that _HUGE_ 70 MB disk fit.

Gerhard

;-)

Yes, but the keyboard trick (patented by IBM, IIRC) worked reasonably well.

Part of (side effect of) the cassette interface, IIRC.

still

Mine are complete units, minus some case screws, perhaps. I don't have the original SS diskette drive, however.

Yes! Xilinx place & route did that once a millisecond to keep the mouse happy.

Gerhard

Was it? It worked fine on the 80286, which didn't have one. And it was entirely done over the keyboard interface. I don't know why the cassette interface would be required. I think that one was supported by the extended BIOS that IBM provided, which included BASIC. I'd have to go back to my BIOS listings (IBM provided them) to be sure, though.

Jon

Well, it was 30 years ago... ;-)

I seem to remember that it was. The cassette port was part of extended BIOS, though you're right it didn't exist after the 5150.