Niezgodka wrote:

- it has 360KB 5.25 FDD. Can I change it to 1.2? Can I put 1.4 3.5 FDD. Will biosthe system honor such new hardware? 😀

HD floppies (both 5.25 and 3.5) need a special FDC (floppy disk controller) and a BIOS that support it. I don't know what kind of FDC has your PC-10, but if it only supports DD floppies it won't matter if your BIOS support it (hint: if your BIOS supports HD floppies, your FDC will be fine).

Niezgodka wrote:

- HDD. It has that 8bit IDE XTA HDD. Is there a way to connect regular HDD? I was thinking about ISA I/O card, with IDE connector. Will XT be able to recognize such format?

Look for XT-IDE and derivatives. Original XT-IDE has IDE but you can connect IDE-CF or IDE-SD adapters, there are derivatives that directly allows you to use CF cards.

Niezgodka wrote:

- 360KB dos. What is the higher DOS version I can install on it? Can I put 6.22 on 360KB floppy?

Every DOS can run on an XT, but later DOS version needs more RAM to work (=you get less free memory). IMHO the "sweet spot" DOS is Compaq DOS 3.31a because it will support HDDs bigger than 32Mb (other DOS 3.x are limited to 32 Mb partitions) and doesn't take as much memory as DOS 5 and 6. If you're planning to put a HDD or flash card less than 32 Mb (or you don't mind the disk space lost), any DOS 3.x would be fine.

I guess that you can even format a 360Kb floppy and put DOS 6.22 system files on it, but there won't be space for much more. I'd suggest you to put a 3.5 inch floppy as a first floppy drive and use your 5.25 floppy as a secondary one (or even put a Gotek or HxC drive as first drive).

Did you remove the battery yet? If not, do it immediately!

Niezgodka wrote:

- 360KB dos. What is the higher DOS version I can install on it? Can I put 6.22 on 360KB floppy?

MS-DOS can be anything from 3.3 to 6.22 (7.x includes 32-Bit code).
In case of 6.x, yes you can. Microsoft once offered 5.25" (360K ?) disks via mail order.
DOS 2.x is pretty much useless (too many limitations), except for maximum compatibility with early software.
All versions of IBM PC-DOS are able run on 16-Bit x86 processors. v3.3 was the last one with XTs in mind.

Alternative DOSes, like FreeDOS (special), Novell DOS 7, PTS-DOS (v6), DR-DOS, DOS Plus and PC-MOS/386 (v3 ?) can run on XTs, too.
Some of them support UMBs even, just like DOS5/6 does, which is nice if your XT is upgraded and you have many drivers to load.
Otherwise, DOS 3.30 (IBM, Compaq) is fine, too, as it has a lower memory footprint.
If you need a mass storage, you can also give ZIP drives a try.
The DOS driver makes use of 8018x or V20/V30 instructions, but there was also a patch, I recall.

Is there any bios enterance? I tried to swap 360KB floppy drive with 1.2mb, but it didn't recognize it.
How come people have different drives on it, like 1.44?

Niezgodka wrote:

Is there any bios enterance?

No, there is no BIOS setup. The BIOS autodetects hardware, and that's it.

Niezgodka wrote:

I tried to swap 360KB floppy drive with 1.2mb, but it didn't recognize it.
How come people have different drives on it, like 1.44?

I don't think the BIOS and FDC can support 1.2 or 1.44 MB drives. 3.5" 720k drives and 5.25" 360k drives work.
If the FDC supports HD drives, then you can get around the problem that the BIOS doesn't detect it, by configuring the drives manually in config.sys (that requires a drive that can boot, so either you need a 5.25" 360k drive A:, or a HDD to boot from).
You can do that via DRIVPARM: http://www.easydos.com/drivparm.html