EMS boards

[Torinde]

I try to make a config emulating a EMS board(s) for running Win3.x in real mode.

When I set ems=emsboard and memsize=128 at DOSbox prompt in MEM I still get XMS = EMS = 128, where I expected EMS to be 32MB (or less) - probably related to #3800.

• clear, EMS supports up to 512MB LIM4.0-compatible extension. memsize=1024 correctly results in XMS=1024, EMS=512.
• problem is with memalias=26, memsize=1024 and ems=emsboard - result is ~64MB for total, XMS and EMS, where I expected only XMS/Extended to be limited to ~64MB (26-bit address lines), while EMS to be 512MB and total to be ~64M+512M

At ems.cpp I see a few TODO notes, which seems relevant.

What is the difference in behavior between the ems=emsboard and emm386 settings?

• on 8086 appears LOG: CPU is 286 or lower, setting EMS emulation to ems=emsboard and disabling VCPI and v86 startup
• on 386 there is a 384K extra usage - probably means that up to 384+64 extended is used emsboard and above that emm386 - LOG: EMS:Unable to allocate EMS system handle. disabling VCPI

Can I have multiple boards for a total of more than 32MB EMS? Now I see that DOSBox gives up to 512MB EMS and that's good!

• at less than 512MB RAM: EMS =XMS = RAM-1
• at more than 512MB RAM: XMS = RAM-1, EMS=512

(actually, it's not "-1M", but -1M -64K (for HMA) -384K (equal to UMA, but it's already in the first megabyte, so why counting that twice? Also, when extended memory capacity is small - only 64K are utilized...)

Drivers and information about LIM specification and Intel Above Board Plus 8 - memory card using EMM.SYS:

• Conventional memory backfill (to increase it to 640KB for PCs with less)
• Mappable conventional memory (window from inside the first 640KB) - for DESQview, Win2.0
• Expanded memory (window from inside the Upper memory 384KB) - for DOS LIM applications
• up to 14MB per card
• multiple cards, up to 32MB total per PC (what will happen if 4x14MB=56MB are installed?)

EMS4.0 compatible superset 64MB:

• NEC Vadem VG230 (VG330 supports only 16MB) - 286 real mode CPU (datasheet)
• C&T F8680 emulation - 186 with 26-bit addressing #5261

Other variants:

• LIM3.0 (for Win1.x?) Emulate LIM EMS 3.0 compatible expanded memory 86Box/86Box#4054
• LIM3.2
• EEMS
• LIM4.0 16-bit ISA expansion card that can expand up to 32 MB, EMS, UMB, XMS (286+), 8-bit ISA compatible, PC/XT/AT/386/486 [FEATURE REQUEST] Orchid RAMQuest 8/16 86Box/86Box#4528
• LIMulator - EMS on HDD (like Above Disc driver, but supporting the "LIM4.0 compatible superset" of Vadem VG230 or the F8680A approach or JemmEx-like with 32768 pages for 512MB capacity)
• XMA, JRAM, others? - if a software using those is found
• EMS driver that uses host RAM (or such option in the LIMulator) - maybe based on hardware driver, JemmEx or 386MAX
• EMS driver option to use HDD space not managed by DOS (e.g. another partition/unpartitioned area or another HDD, even on additional controller) - that can be useful also on bare metal with (XT-)IDE SSD/RAMdisk, PicoMEM/FPGA/etc.

DOSBox EMS on 8086/186 skips the first 64KB - I assume because it inherits the mechanism from EMM286/EMM386. I think in emsboard case the first 64K should not be skipped.

XMS driver for 8086/NEC/etc.

• provide XMS/HMA by using EMS/UMB/file/conventional/etc. (same places as above) - it seems DOSBox already does that now, but marks it as used? Can it become free to use by programs/Windows/etc.?
• aligned with GLaBIOS/emulator if custom BIOS is needed for something, e.g. HMA/Gate A20 emulation

XMS driver examples:

• AST Research shipped EMS boards with REX.SYS (unclear if applies to PC/XT)
• Intel Inboard 386 (add-on for PC, XT) - utilized DOS drivers to configure the onboard memory.
• PCE emulator - XMS, UMB, HMA on 8086
• XMS, HMA on V30 add-on for Atari ST - Extended memory emulation using the host system capabilities
  -- EXTMEMS.SYS from SOFTBYTE

Programs mentioning XMS separately from Extended memory:

• Dune 2
• GeoWorks 2
• Space Quest

Besides PC/XT, 24/26-bit 286/386/486 machines also can benefit from additional memory - both EMS and XMS.

• backfilling Conventional memory up to ~1MB (-8KB on PC, full 1MB on custom hardware/emulator)