Reposting and summarizing, for your information or additional comment.  *** THIS IS LONG ***  I have 16MB of memory on my 386SX (25 MHz), an Intel math coprocessor, and a 120MB hard drive with 20MB free (no compression).  I have been running Mathcad 3.1, under Windows 3.1 in enhanced mode, with a 5MB RAM drive, 2MB/1MB Smart drive, and no swap file (permanent or temporary) for several months.  I am interested in the faster Mathcad 4.0, but I am concerned about reported swap file requirements and the legitimacy of Mathsoft's claim about increased speed.  TO 386SX USERS:    Will Mathcad 4.0 run without a swap file, or insist that I use a swap file?  So far, in response to a less detailed description of my setup, or in unrelated postings, the more informed answers, on the net or by E-mail, appear to be:    1) by fuess@llnl.gov (David A. Fuess) >>     >> According to Mathsoft, no. Mathcad uses the swap file extensively so as    >> not to overburden the physical resources. They say this is actually a    >> win32s feature. A figure of 10MB was indicated to me as a minimum. But    >> you might try anyway!    2) by bert.tyler@satalink.com (Bert Tyler) >>     >> I'm not all that certain that Mathcad is the culprit here.    >>    >> I have a 486/66DX2 with 16MB of main memory (less 2MB for a RAMdisk and    >> a bit for a DOS session that is opened as part of the startup process),    >> which I have been running without any swapfile.  When I installed the    >> WIN32s subsystem from the March Beta of the NT SDK, the WIN32s subsystem    >> itself demanded the presence of a swapfile.  The only WIN32s program    >> I've run to date is the 32-bit version of Freecell that came with that    >> subsystem.    >>    >> I gave Windows a small temporary swapfile (I'm leery of files that must    >> remain in fixed locations on my hard disk), and all seems well.    3) by bca@ece.cmu.edu (Brian C. Anderson) >>     >> What is Win32?  I upgraded to Mathcad 4.0 and it installed a directory for    >> Win32 under \windows\system .  During the upgrade it told me that win32    >> was required.    4) by case0030@student.tc.umn.edu (Steven V Case-1) >>    >> MathCad 4.0 makes use of the Win32s libraries.  You've probably   >> heard about Win32s, it is a 32-bit Windows library that provides   >> much of the Windows NT functionality (no support for threads and   >> multitasking and such) but can be run under Windows 3.1.    5) by rhynetc@zardoz.chem.appstate.edu (Thomas C. Rhyne) >>     >> I also have 16 Mb of ram, and indeed Mathcad 4.0 insisted on a permanent    >> swapfile; it would not run otherwise.    6) by bishop@baeyer.chem.fsu.edu (Greg Bishop) >>     >> 3) MathCAD absolutely requires 4MB RAM (with 12MB swap file) or 8MB RAM    >> (with 8MB swap file).  It will give you a not enough memory error if the    >> swap file is less than 8MB.  It is a MAJOR resource hog.  If you do not    >> load the symbolic processor or the smart math, it takes about 5MB of RAM    >> (real or virtual) just to load (again, due to the win32s libraries.  ******************************************************************************** *                                                                              * * So it seems that in addition to the system requirements shown on Mathsoft's  * * advertisement for 4.0, that you need a swap file, possibly as big as 12MB.   * * Looks like I would just need an 8MB swap file, and would need to choose (or  * * can I?) between a faster permanent swap file, or a slower temporary swap file* *                                                                              * * Apparently a Win32 subsystem ships with Mathcad 4.0 - how much disk space    * * does this require?                                                           * *                                                                              * ********************************************************************************  I also received these answers:    1) by mfdjh@uxa.ecn.bgu.edu (Dale Hample) >>     >> If you've got 16 megs of RAM, why not configure 10megs as a ram disk for    >> Mathcad?  DOS 6 permits different bootup configurations.  ******************************************************************************** *                                                                              * * Can Mathcad 4.0 + Win32 be configured to use such a RAM drive instead of a   * * swap file?  If not, I don't see how using DOS 6.0 for an alternate bootup    * * would provide Windows with this swap file.   Some time back I remember a     * * discussion about the issues of using a RAM drive to support a swap file,     * * but I thought this involved slower, < 8MB systems.                           * *                                                                              * * I have DOS 6.0 but for various reasons have not yet done a full installation.* *                                                                              * * By the way, is a full installation of DOS 6.0 required to avail oneself of   * * the "alternate bootup" feature?  Which files from the installation disks are * * required?                                                                    * *                                                                              * ********************************************************************************    2) by wild@access.digex.com (Wildstrom) >>     >> Presumeably, you mean without a _permanent_ swap file. If Windows needs a    >> swap file, it will upo and create one if a permanent one doesn't exist.    >> Permanent is generally faster though. I don't know why Mathcad wouldn't    >> be happy with either type--Ver. 3.0 is and so should any program conforming    >> to the Win specification.