wrote:I also have a 8087 laying around, don't think I'll install it though - same as having a 287/387 IMHO , almost useless 🤣
It will prevent unpatched OpenWatcom C binaries from locking up the machine if anything 😀
(They have a bug in their FPU detection routine, which doesn't affect 286 and higher systems, probably never tested on real hardware).
wrote:Not 100% plain sailing of course... Carlos' HD floppy bios detects the Gotek as 720k, not 1.44MB.
It also causes the 360k drive to make horrible screeching sounds during drive detection 😒
2M-XBIOS works though, so I think the hardware is OK. I may try some other HD floppy bios.
That's weird my Gotek got detected as 1.44MB just fine. I wonder if i made any mistake while building the file... I think i have other options which i can probably post later.
It may be something to do with the HxC firmware.
OK, played around with some alternative HD floppy BIOS...
The one that works the best for me is from Sergey's floppy controller project: http://www.malinov.com/Home/sergeys-projects/ … sa-fdc-and-uart
It allows the drive configuration to be specified manually by editing the BIOS.
I found it was necessary to put the floppy bios first when combining it with the XT-IDE BIOS.
Works really well, although it seems slightly slower than the other BIOS. I was able to boot from a 1.44MB disk image on the Gotek.
Cleaned the inside of the full-height IBM floppy and lubed the rails with some silicone spray. It's much happier/quieter now.
Jeff has fixed write support on the HxC Gotek so all is good there too.
The 8284 clock generator on my XT board is socketed, I've been playing with the idea of getting a PCB made up a PC-Sprint clone. This would boost the cpu to between 7-8Mhz.
wrote:The 8284 clock generator on my XT board is socketed, I've been playing with the idea of getting a PCB made up a PC-Sprint clone. This would boost the cpu to between 7-8Mhz.
Perhaps this information is useful to you? http://www.brutman.com/pcsprint_annotated.zip
Thanks - will probably try Sergey's modified version with auto downclock on DMA.
Crap picture of Sergey BIOS in action
Update... managed to skip the floppy seek test by hacking the floppy BIOS. I'm fixing some minor issues with the 5153 monitor which look like they're down to a couple of bad caps. I also think the XT PSU needs recapped.
I've gone back to the IBM CGA for this machine. It's been an interesting experience finding out what makes sense and what doesn't for an original XT. While a lot of upgrades are possible, they don't necessarily make sense. Here's my conclusions:
- EGA card: works fine and CGA compatibility is good if you pick the right card. However, most/all EGA games run too slowly. The best thing about it in an XT is that you don't get snow. However, you lose one really unique feature of the original IBM CGA - composite output. This is a big minus in my book, so I'm sticking with the CGA.
- EMS card: Cool, but it's kind of pointless. The driver uses up valuable conventional memory. If you need EMS you also need a faster machine, at least a 286. I'm moving mine to another machine.
- V20: No real downsides bar a handful of games won't work. Really cheap speed boost and takes a lot of games from being slightly sluggish to playable.
- 8087: No downsides, get one cheap on eBay.
- SB16: No downsides and you get a joystick port and volume control for PC speaker! There may be one or two games that can use Adlib.
- XT-IDE: Works great, no downsides
- Gotek: Works great, no downsides
- High density floppy controller: Well.... I was never 100% happy with mine. Maybe the controller was bad, but I got some intermittent problems. So, I've gone back to the IBM controller. With the Gotek there's no issues with finding DD disks.
Basically, the same conclusions Great Hierophant comes to in his blog.
I can only comment that another person that also built the EMS card came to the same conclusion and advised me against building it. They said that the 1MB ramcard Lo-tech sells that can provide UMBs is more useful.
Can definitely see that, if you have a configuration that requires many drivers e.g. SCSI, network.
A bare-bones DOS 5.0 config with keyb and cutemouse gives me ~580K free conventional memory.
I haven't found any games that require more than that and would still run on an XT.
Small update to this system. Replaced the SB16 with a Pro 2 so that the POST beeps are audible. The SB16 mutes the PC speaker input on cold boot.
Was also getting occasional hangs on boot so I replaced the CF adapter & card with DOM that plugs directly into the IDE socket, seems good so far.
After the EMS experiments I decided getting some UMBs would be more useful for this system. So I built a Lo-Tech 1MB expansion card, it can provide memory in 64KB blocks. Assembly isn't too bad apart from those small resistor arrays. I had to use desolder braid a few times to fix shorts on them.
This is a CGA system with hard drive, so it has free memory in the A000, D000 and E000 ranges for a total of 192KB of UMB.
Using USE!UMBS and DOSMAX I went from 560K to 630K free conventional. Not bad eh
nicely done!
Which games won't run on a V20? As far as i can remember Lode Runner required an 8088 but the DOS conversion was patched so it runs on a V20.
