Hi, On Thu, Jun 30, 2016 at 6:51 PM, Abe Mishler <a...@mishlerlabs.com> wrote: > >> On Jun 30, 2016, at 6:19 PM, Rugxulo <rugx...@gmail.com> wrote: >> >> If JEMMEX is your only problem, then you have no problems. > > This idea has appeared before in this thread and it is a relief to hear it > echoed. > Perhaps a disclaimer like this is warranted in the Wiki install guide for new > users > like myself. (I had very limited exposure to DOS when it was mainstream so > the idea > of so many different memory modes has been overwhelming to learn suddenly.)
I didn't have a PC back then, but AFAIK .... The IBM PC used an 8088 in 1981. The max memory supported was 640 kb (low / conventional), but even that was usually overly idealistic. I think?? you typically got 400 kb free back in those days (if you could even afford the full 640 kb at all). The original IBM PC didn't even have a hard drive, and it shipped with like two 160 kb floppy drives. I think 64 kb of RAM was the initial amount (similar to CP/M, I suppose). Only later did 500 kb RAM free become the norm and even required, e.g. MS-DOS 5 bragged about freeing up "45 kb at least". Of course, originally it was optional things like (hardware) EMS that (partially) brought more RAM. That was presumably more common with 8086-ish machines than newer ones. With the 286, although it took a while to standardize, the preferred approach was either "raw", XMSv2, or DPMI (which really sat atop one of the others). Even DPMI didn't appear until 1989/1990 with Windows 3.0. The 286 was, what, 1982? Obviously the 386 was (first) introduced in 1986 by Intel. But the IBM PC didn't get the 286 until (I don't even know) XT? Nope, Wikipedia says "XT 286" was 1986. Nope, Wikipedia also says "The 80286 was employed for the IBM PC/AT, introduced in 1984". But it took a *long* time for megabytes of RAM to become common. It was just too expensive. (My 1994-era 486 Sx/25 only had 4 MB.) Long story short, the differing memory APIs were due to different hardware. So hardware "expanded" (EMS) needed one API while the 286 (max 16 MB RAM)'s "extended" (XMS) memory needed another one. And Windows 3.0 (1990) invented yet another one (DPMI) that was "better" than VCPI (and more widely supported, although most DPMI servers ended up being 386+ anyways). > If a consensus can be reached, I would humbly submit the idea of swapping > options 1 and 2 in the next release to give less emphasis to JEMMEX. Even Blackthorne (game, which is now freeware BTW) required EMS, and that was what, 1990s?? (Wikipedia says 1994.) So we can't totally say that nobody should or can use EMS (e.g. EMM386). But yeah, I agree, JEMMEX as default isn't really all it's cracked up to be (due to various rare quirks, among other reasons). > As a new user, I naively thought that JEMMEX was the best/preferred option > based on its ranking which may be intended. In theory, if everything was perfectly bug-free, then sure, having both XMS and software-emulated EMS (via V86 mode) + VCPI and using UMBs (leading to more conventional memory free) is perfectly ideal. (DPMI is usually loaded on demand via separate TSR.) Obviously, in hindsight, you don't really need a billion APIs for the same family of hardware. But that's the point, FreeDOS tries to support 8086, 286, and 386 memory schemes (but no AMD64, obviously). > But under the example of VBox, it doesn't hold up. I think I have learned now > that even though JEMMEX claims > to do the same thing as option 2 in less memory by combining driver logic, > option 2 really works better even if > there is a slightly larger overhead. The more differing environments, the more testing you have to do to support them all. It can add up, leaving obscure bugs. > Option 2 certainly gives me more expanded memory (EMS). Not sure why, offhand. > At least this seems to be the case in VBox. However, JEMMEX behaves just fine > running under QEMU. > So go figure. Perhaps the Wiki should push people towards QEMU on Linux > rather than VBox on Windows. No, because most people don't need JEMMEX and/or EMS, and VBox (sometimes) has other advantages. It's not worth giving up the whole environment due to one or two accidental incompatibilities. But I agree, in theory, that JEMMEX shouldn't be preferred or suggested without a good reason. But that's not my decision for FD 1.2 (and I forget offhand what Jerome uses, I haven't downloaded any recent prereleases, too preoccupied with other bagatela). ------------------------------------------------------------------------------ Attend Shape: An AT&T Tech Expo July 15-16. Meet us at AT&T Park in San Francisco, CA to explore cutting-edge tech and listen to tech luminaries present their vision of the future. This family event has something for everyone, including kids. Get more information and register today. http://sdm.link/attshape _______________________________________________ Freedos-user mailing list Freedos-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freedos-user
