Very few programs are compiled specifically for the Pentium 4. This is because it makes the code unable to run, or perform worse, on other processors, such as a Pentium III, Athlon 64 X2, or Core Duo. Also, there have been several iterations of the Pentium 4, each adding new features, like SSE2 and HyperThreading.

One example of a program compiled with some Pentium 4-specific optimizations is Swiftfox, a recompile of Firefox on Linux.

Internet Explorer, mostly since at that time google chrome and opera or maybe even firefox either didn't exist or were too new, IE was also the default for pcs, which were more popular, and still are, than macs so IE beat safari. Also, Internet Explorer 9 is faster now. People say chrome is faster, but on slow systems, based on personal experience and proof, IE is too slow to use(unless you disable add-ons), but on newer, faster systems, IE IS better. However, the usage % as of April 2012 is close. Here it is:

Internet Explorer ......25.93%

Google Chrome .........24.99%

Mozilla Firefox ...........21.79%

Apple Safari* ............14.09%

Opera ........................5.04%

Android-Based ...........3.18%

Other Browser** .......4.98%

*Not counting IOS usage

**Such as Avant Flock Sleipnir K-meleon Netscape

Maxthon RockMelt Seamonkey Slimbrowser Element

iCab Konqueror Swiftfox Camino Dreamcast and

about 25+ more.

..............................Mostly used ...........2nd

In: North America ..........IE............... Chrome

South America ..........Chrome ................IE

Asia ..........................Chrome ................IE

Europe ......................Firefox .........IE/Opera Tie

Australia .......................IE............... Unknown

Africa .........................Firefox .................IE

Antarctica/NP ............Firefox .................IE

So anyways in the past and now Internet Explorer is the most used. Bet you didn't expect such a deatailed answer, did you? Have a nice day!