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Re: Floppy disk write sector vs implied seek?

If the disk is ejected during seeking, the seek would complete without issues (the drive's step motor is still going to move the head), but the read command is not going obtain any data from the drive, and therefore most likely time out, which would cause DOS to report "Not ready reading drive A:". …

Re: Floppy disk write sector vs implied seek?

When does a write command perform implied seek? Before or after the data transfer to disk? Before. If implied seeks are enabled, when a READ SECTOR ID, READ TRACK, READ DATA, READ DELETED DATA, WRITE DATA, or WRITE DELETED DATA command is issued, the FDC compares the specified sector ID's cylinder …

Re: DOSBox vs PCem vs 86Box which do you prefer?

I also ended using 86box over PCEm for the better interface, but v17 brings optimizations that make it run much faster, and don't seem to be applied on current 86box builds. On my PC 86box can run POD on Windows 98 without CD music skipping on a P166MMX... PCEm v17 can do it on a P233MMX. Same with …

Re: (S)VGA 256-color shift and Chain 4

I found your old posts about that stuff, and they match what I observe as well, and the OS/2 ET4000AX driver does the same thing - sets 256 color mode, without Chain 4, but expects to be in Chain 4 mode. On your end, I see that you simply patched the registers used, but there must be a better way to …

Re: (S)VGA 256-color shift and Chain 4

But then why is it expecting to be in Chain 4 without Chain 4 being set? Edit: So then Shift 256 is OR'ed with Chain 4? That might be true but then wouldn't the Windows 95 boot screen and Wolfestein 3D both break since I have observed both of them using 256-color planar mode? Edit #2: Reading the …

Re: (S)VGA 256-color shift and Chain 4

The OS/2 ET4000AX driver also writes to sequencer register 0E (which is entirely undocumented!), setting bit 1. The Windows 3.x ET3000AX driver sets bits 4 of attribute register 0x16. Edit: And I'm running the actual BIOS'es as well. What I see, with both of those drivers, is the card being put into …

(S)VGA 256-color shift and Chain 4

On real hardware, does the the (S)VGA 256-color shift (GDC register 5 bit 6) force the video memory into Chain 4 mode regardless of sequencer register 4 bit 3? Or is that a Tseng-specific thing? Because I have two different Tseng drivers, the Windows 3.1 driver for the ET3000AX and the OS/2 "SVGA" …

Re: VGA difference of blacks?

If SVGA monitors use the same specifications as (non-Japanese) NTSC, then blanking would be at 0%, while the active display (black to white) levels would be at 7.5% to 100%. But I'd look up actual (S)VGA documentation for that instead, perhals look up the voltage range and convert it to %, and then …

Sound Blaster filters and CD Audio

Does the Sound Blaster apply any of its filters (low-pass, treble, and bass - not all Sound Blaster versions have all of these) to the CD Audio it gets by cable from the drive? Edit: And what about OPL? Do those filters get applied to the OPL?

Re: PS/2 mouse on IBM PS/2 models 25-8086 and 30-8086

So, if I understand correctly, on PS/2 Model 25-8086 and 30-8086, keyboard, mouse, and RTC alarm are all on IRQ 1, and IRQ 1 always issues INT 71h, whose BIOS handler then demultiplexes it to INT 70h, IRQ 1 INT (with base read from port 63h), and INT 73h. Looks like I'll need to add this special …

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