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You know There are several IBM Trademarks : PC , XT , AT , PS/2 ..and when you write device drivers , you see some differences ( e.g. FDC Diskette Status Register A at 3F0h in PS/2 only ).

As you know , we can Check the model from the byte 0xFFFFE in memory .
In my computer this byte is 0xFC which means : AT , XT , PS2 ..it supports all of them !
okay , does this mean that i can write my drivers ( suppose writing to my pc ) whih no care of the mode ?
another question :
These IBM Models are too old , suppose that I'll write my os to work on modern IBM-Compatible PCs or on most currently-used IBM-Compatible PCs , what the model I have to write to ?

   Thanks , & sorry to speak too much .

Hi

First of all, unless your writing a Real Mode OS, forget the PC and XT, they use the 8088 CPU. Also, unless your going to put in support for microchannel, forget PS/2. This just leaves AT. But watch out, the IBM PC-AT only has a 286 Processor. So technically, if your doing a paged OS rather than segmented, you should choose none of them! But all the 386 AT clones and up (My main PC is an Athlon XP based AT clone, with extra bits ).

As for Ports, Interruptes, I'd Suggest The indespensible Hardware book [Messemer] and The Undocumented PC [van Gilluwe].

These will also show you the differences in the PCs throughout history.

hope this helps
srg

I think you have mis-understood me , I have Celeron Processor
with 2000 MgHz , the Motherboard form factor is ATX , I know that trademarks AT,PS/2 ..etc) are old however they are existant in most docs relating to os development , this make me thought that these are standards .
for example , during the writing of fdc driver , all docs i found
were speaking in terms of AT,PS/2,...

so , they are still in use as standards ???

thanks

well, our keyboards are still programmable as 'AT keyboards' and most non-USB mice are PS/2 ... both 'PC' and 'XT' are totally obsolete and you probably won't find any stuff like them. There are more recent 'guidelines' for hardware manufacturer like "PC98" or things alike, mainly driven by MS, iirc...

firas981 wrote: I think you have mis-understood me , I have Celeron Processor
with 2000 MgHz , the Motherboard form factor is ATX , I know that trademarks AT,PS/2 ..etc) are old however they are existant in most docs relating to os development , this make me thought that these are standards .
for example , during the writing of fdc driver , all docs i found
were speaking in terms of AT,PS/2,...

so , they are still in use as standards ???

thanks

Different IBM models were programmed and had their quirks in slightly different places. All modern PCs are based on the PC-AT and the 386 CPU (later CPUs had more instructions.)

So, when they say, "on the PC do this, on the PS/2 do that, on the AT to the other", then you follow the AT route.

Bringing up your example of the floppy drive, the PS/2's floppy drive controller has three status registers that none of the other IBM models, including the AT and so all modern PCs have.

ATX is just a motherboard specification, AT, PS/2 etc were models of IBM's original x86 based line of personal computers.

Maybe a little bit of histroy is in order:
* First there was the PC, with 2 floppy's, 8088 and 8-bit bus.
* Then the PC-XT (Xtended Technology, replacing the PC), this had only one floppy and a 10MB hard drive + CGA graphics AFAIK.
* Then came the PC-AT (Advanded Technology, this replaced the XT). This introduced a 20MB hard drive, 16-bit bus (later called ISA), a CMOS RTC (on the PC & XT you had to enter the time and date every time you used it), 286 CPU and EGA graphics AFAIK.
* After that, IBM got greedy. The AT/ISA bus was an open standard, but they launched the PS/2, to replace the AT, and used a proprietry BUS standard called MCA (Microchannel).

In the end, The PS/2 flopped, IBM lost their virtual monoply and effectively handed it to Micro$oft.

The PS/2 died away, leaving the AT clones, the grandfathers of modern PCs.

Oh, the other one you may have heard of, EISA, was an open standard AFAIK in competition with Microchannel. Both were 32-bit (although EISA was also backwards compatible with ISA cards). They both flopped (I've read on motherboards.org that it was because of Intels high licencing that killed EISA off, pushing for their PCI. If true, then it's a rare example of how Intel's anti-competative antics have actually helped push better technology).

Anyway, on EISA and MCA, there are more timers and better DMA and PICs, although their both different from each other.

Anyway, just go AT.

srg

Thank you srg , your reply is very nice , and I have got the image very clearly .

thanks