There is an excellent, in-depth, well-argumented article by Geoff Chappell on the issue. Highly recommended in its entirety to those who want a complete understanding (additional side-reading and facts verification might be necessary).

A single citation to get you started:

There is already on the Internet and elsewhere an awful lot of rubbish to read about this question. Hardly any of it would be worth citing even if I didn’t want to spare the authors the embarrassment. A surprising number of people who claim some sort of attention as expert commentators would have you believe that using more than 4GB of memory is mathematically impossible for any 32-bit operating system because 2 to the power of 32 is 4G and a 32-bit register can’t form an address above 4GB. If nothing else, these experts don’t know enough history: 2 to the 16 is only 64K and yet the wealth of Microsoft is founded on a 16-bit operating system that from its very first version was designed to use 640KB of RAM plus other memory in a physical address space of 1MB. Some remember this history and add seemingly plausible qualifications that exceeding 4GB is possible only at the price of nasty hacks that require everyone—well, all programmers—to jump through hoops. Fortunately, Intel’s processors are a lot more advanced than the 8086 from all those years ago.

P.S. Unfortunately, patching the kernel won’t help make Windows XP see more than 4GB RAM: even though the kernel itself does support more RAM (with PAE), starting with SP2 the HAL was modified in a way prohibiting access to any RAM beyond 4GB. Patching may only be suggested to devoted geeks with Vista’s and 7′s.

Ideologically correct solution is offered by Panda software – a free Panda USB and AutoRun Vaccine. It can do two things for your Windows box:

1. with a single click disable auto-execution of programs from USB sticks and CDs/DVDs, and
2. with one more click – make the autorun.inf file on your pendrive inaccessible, so as to prevent infecting your USB stick with an “autorun.inf virus”.

Program does not require installation, but requires Administrator privileges. It supports FAT/FAT32 pendrives, but NTFS-enabled version is being tested and should be made available shortly.

Note, that if you perform step 2, re-enabling access to autorun.inf may require pendrive formatting. Also, after step 1 your favourite CDs and DVDs won’t start automatically anymore – but you will be able to start them manually.

And, of course, Linux users have nothing to worry about (yet).

running UNIX applications (via SUA, Subsystem for UNIX Applications) , which provides higher flexibility for Windows workstations.

Where is the world going?

And how soon will all the Windows users (not only Ultimate Users) benefit from the higher flexibility by running UNIX applications?

Warning: you proceed at your own risk. If you do not know what you are doing – please don’t

Download (original) French gpedit-pour-xp-home.zip.

Download English gpedit for windows xp home.zip (also in 7zip archive).

Here are instructions for manual MMC snap-in installation. Original French-version archive had a batch file which does installation automatically, which I also added to the English archive (gpedinst.bat). But you must manually verify that batch file fits your system before running it! It might be safer to follow the instructions manually.

• Put these files:
  

  appmgmts.dll
  appmgr.dll
  fde.dll
  fdeploy.dll
  gpedit.msc
  gpedit.dll
  gptext.dll

  into %SystemRoot%\system32 folder (most often it’s just c:\windows\system32)

• put these files:
  

  system.adm
  inetres.adm
  conf.adm

  into %SystemRoot%\system32\GroupPolicy\ADM\ (create if this folder doesn’t exist)

• finally, run these commands one by one in the CMD window:
  

  regsvr32 gpedit.dll
  regsvr32 fde.dll
  regsvr32 gptext.dll
  regsvr32 appmgr.dll
  regsvr32 fdeploy.dll

That should make gpedit.msc callable as Start -> Run -> gpedit.msc.

Other language versions of the necessary files can be retrieved from corresponding-language installations of WinXP Professional; English version can also be downloaded directly from Microsoft website ( e.g. here , or search for “Group Policy ADM Files” at microsoft.com). Also, you can extract necessary files from available Windows distributions: just don’t forget, that “filename.dl_” is a compressed version of “filename.dll”, and can be uncompressed by using XP-bundled extract command.

See also this comment for alternative gpedit installation (get the file from badongo first), and also this comment for one more explanation of manual installation.

Geeks corner:

1. a comprehensive list of the “Group Policy/User Configuration/Administrative Templates” settings in Windows XP Home Edition
2. an extremely comprehensive Excel sheet, which maps numerous *.adm-file options to their registry equivalents – Group Policy Settings Reference (PolicySettings.xls). This file is for Windows 2000, Windows XP, and Windows 2003

Disclaimer: I do not know if modifying (e.g. by adding gpedit) your WinXP HE is a violation of any EULAs. It’s your own responsibility to check this out and comply with any such regulations. Also, be advised that modifying any settings using gpedit.msc on WinXP HE may render some parts of the OS inoperable (in my opinion). You have been warned!

There’s also another one, but provides read-only support.

Topologilinux is a special linux flavour, which is especially fit for the newcomers to the *nix world. The motto of Topologilunux is ‘Running Linux inside Windows’ – and that is what it does. Even more – you can run it inside windows, or you can boot into it and work Linux-only – in both cases the system is the same.
Personally, I consider this kind of setup extremely useful for users who are strongly used to working in Windows (or just stuck with windows for too long), but at the same time are inclined to script a bit (be it bash, Perl, PHP or Python), to run server applications, write cross-platform programs, to test something or just play with software. With Topologilunux, it’s perfectly fine to work in DreamWeaver on your windows machine, and launch Topologilinux with apache+php+mysql to serve as a testing server – on that same machine. You can easily replicate the needed server config, and play with it the way you wouldn’t if that was the production server.

Or, in another scenario, you may launch Topologilinux to write the script you need for your data (for example, Bioconductor package for R statistics environment has many packages available only for *nix systems) without leaving your nearly perfectly set up windows environment; then, when you need to run that CPU-intensive you wrote, you can boot into real-mode Topologilunux, run your analysis, and get back to Windows

All of this is available without the need to re-partition your hard drive – Topologilinux fits into a single image file on your FAT32/NTFS drive of choice. Both installation and removal are very simple (common click-through), with a bit more effort in the networking part (sufficient documentation is available, if not with Topologilinux, then with coLinux).

The only problem I had with Topologilinux was BSOD (Blue Screen Of Death) every time I tried to launch Topologilinux from within Windows. The error was DRIVER_IRQL_NOT_LESS_OR_EQUAL. Searching for troubleshooting required some time and was not evident, so here is what fixed my problem.

The conflict seems to arise from the Data Execution Prevention (DEP) feature of the modern computers, which is intended to protect from the various ‘buffer overrun’-based exploits and hacks. By default, it is enabled for system files and services (equal to /noexecute=optin option in boot.ini). I tried setting it to ‘All files, except chosen below’, then adding colinux-daemon to exceptions, but that didn’t help either. The only option which helped was disabling DEP from boot.ini by adding ‘/noexecute=alwaysoff’ after the line identifying your Windows installation.

Here is a sample line from my boot.ini before modification:

multi(0)disk(0)rdisk(0)partition(1)\WINDOWS=”WinXP Pro” /fastdetect

and after modification:

multi(0)disk(0)rdisk(0)partition(1)\WINDOWS=”WinXP Pro (DEP off)” /noexecute=alwaysoff /fastdetect

Hope this helps you.

Update: since I’ve moved to Debian, I’m no longer using Topologilinux.