Re: Did Commodore cheat with the quad density floppies?

Den Sat, 12 Jan 2019 21:05:28 +0000 skrev smf <smf@null.net>:
> On 10/01/2019 20:05, Mia Magnusson wrote:
> > At the time, companies that had more at stake didn't dare to make a
> > "too compatible" PC.
> 
> I don't think that was true at all.
> 
> The companies with more at stake were because they had been selling
> 8080 machines running CPM-80 and they were waiting for CPM-86 to come
> along as that was going to be the new standard.
> 
> They then took their old 8080 based motherboards and adapted them for 
> 8088, CPM-86 came out but then so did MSDOS.

That might had been true in North America and Japan but not always in
Europe. Afaik for example Ericsson and Nokia never made any CP/M
computers or any computers at all before their first 8088 "DOS"
computers.

Anyway in practice you'd mainly need a PC compatible BIOS (and
reasonable allocation of some of the interrupts) to run many of the PC
programs, and with PC compatible display hardware you could get away
with running almost all PC software even if every other part of the
computer, of course except the CPU, were incompatible with the PC. (As
the PC BIOS did totally suck re the serial port routines, all terminal
software and similar of course actually required an 8250 or 16550 at
the well known addresses and using the well known IRQ's).

The display hardware also only had to be compatible at the video memory
level, not that much at the I/O port level.

Remember that the PC and the XT had a different kind of keyboard
hardware than the AT and all newer PC's. They also had a different
setup for the interrupt controller(s) (with the PC and XT only having a
total of 8 hardware interrupts while the AT and newer had 15 using two
cascaded interrupt controllers).

Also remember that most software ran fine with any kind of disk system.
The XT had a different hard drive controller than the AT, and there
were third party SCSI controllers. The AT's floppy controller added
support for HD disks, which most software ran fine on even if they were
developed before the AT were released.

Almost all software written for the older video standards run fine on
VGA or newer cards. Those cards only has the correct display memory
layout while differing much on the I/O ports. All PC/DOS software called
BIOS to select display mode.

> Microsoft did OEM deals that gave you the source code to the hardware 
> specific part of the OS (I think they shipped the source for the SCP 
> 8086 systems that QDOS was originally developed for, not the IBM PC 
> versions of those files).

This is btw well covered on the blog os2museum, which I really
recommend to anyone interested in the history of the PC and related
stuff.

> You changed the software to match your board and you didn't need to 
> bother cloning the PC because all the applications will work anyway
> right?
>
> Well soon it became clear that wasn't true & people only wanted to
> buy clones. But clones were being made at the same time.

Sure there were an overlap in time, but at that time it was only
companies who were prepared to risk everything that did produce clones.

Later when nothing bad did happen to them, the older more established
companies did dare to start producing clones.

Having separate companies producing the compatible BIOSes, like for
example Phoenix and AMI, also did help as it made the legal situation
more safe for a clone manufacturer.
 
> When I went to college in 1987 the dbase stuff we did was all on CPM, 
> which is kinda insane.

In grade 7-9, in the mid-late 80's, we had the Swedish for-schools
produced computer "Compis" which used an 80186 and usually ran CP/M-86
but could run MS-DOS although not PC compatible. Back in the days those
computers were afaik actually a reasonable choice for running Autocad
as the 80186 were far faster than an 8088 and those computers had
rather good graphics. Afaik they always had something like 640*400 or
maybe 800*400, and with color hardware they could produce at least 8
colors (probably 16) in full resolution.


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