On Tue, Sep 1, 2020 at 1:35 AM Jon Brase <jon.br...@gmail.com> wrote: > > > Not that convincing rationale considering rather modest overhead necessary. > > Recall that FreeDOS isn't just about having a FOSS alternative to MS-DOS for > modern machines (where you're really better off just using Linux and DOSBox), > or for your early-90s 486 retrogaming machine, it's also meant to be an > alternative to MS-DOS for the very oldest PC hardware, all the way back to > the original IBM 5150. The core software might therefore be expected to work > in very little RAM. As I recall, the minimum configuration for the 5150 had > only 16k of RAM. A decent laptop these days will have more 16k blocks of RAM > than a minimal 5150 had *bits* of RAM. So for FreeDOS to work on such > machines, it has to treat kilobytes like young whippersnappers like me treat > gigabytes. 500 or 800 bytes starts looking pretty expensive at that rate.
And just who still *has* a working 5150 with 16KB RAM and doing what with it if they do? (For that matter, who is still running original ancient hardware that *hasn't* taken it to the full 640K of supported user memory?) The earliest 5150 model could take 64K on the motherboard, but later models increased that. (The 640KB limit for user accessible RAM was an IBM decision. The 8088 CPU has a 1MB address space.) The earliest versions of DOS looked a lot like CP/M under the hood, which is unsurprising. The previous range of machines the IBM PC was designed to replace were boxes from manufacturers like Osborne and used the Intel 8080 or Intel compatible Zilog Z80 and ran CP/M. Those earlier CPUs had a 64K address space (and some of the machines came with 48K of RAM.) A design goal for the earliest PC was to make it easy to port software originally developed on CP/M machines, like WordStar and VisiCalc, to the new architecture. While early PCs might have been released with as little as 64K of RAM, more was common. (A machine at a former employer had 256K.) Pretty much everything got extended to the full 640K main memory to accommodate RAM hungry applications. (Think Lotus 123, and larger and larger spreadsheets.) Complaints that changes like this make them harder to run on really old kit are only meaningful if someone is *trying* to. I think even the "pure DOS machines" folks here who *only* run DOS have machines with 640K, and possible expansion RAM in EMS or XMS flavors. ______ Dennis _______________________________________________ Freedos-user mailing list Freedos-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freedos-user
