Answer I give to these questions:
PHP, [www.php.net], while loosely based on C and Perl, has never faced the overwhelming complications ASP has. PHP is an object oriented language - though scripts need not necessarily be developed that way (there are still a vast number of developers preferring procedural programming, and PHP caters to both schools). PHP is both cross platform and open source, available for every major operating system and works with most web servers. It is easily extendable by anyone capable of coding in C, and comes pre-bundled with more functionality than ASP could ever offer. Simple capabilities, such as FTP, data compression, file uploads, XML, MD5, encryption and email are not included in ASP and require expensive, third-party packages to be installed. All of this functionality and more are built right into PHP. Complex functions such as dynamic images, IMAP, SNMP, dynamic flash, PDF, native access (non ODBC) to Oracle, Ovrimos, Postgre, Sybase, mySql, MSSQL, Ingres, Interbase and Informix databases, LDAP, and sockets, just to name a few, are available for free to any installation of PHP, but are not (and probably never will be) available with ASP. In addition, one could make the point that PHP is a more mature language than ASP. ASP has only been around since 1996; PHP has been around since 1994, and has a huge base of developers working on it every waking minute of every day; bugs are usually fixed within minutes of being reported and new features are being integrated daily.
1) ASP is significantly slower than PHP, for obvious reasons. Primarily, PHP runs on notoriously fast Unix and Linux servers which have for years outpaced Windows running on comparable hardware. ASP does not run on any operating system other than Windows, and even then, only in IIS and PWS. I could discuss countless reasons why IIS makes a terrible web server, but that would be a discussion all on it's own. PHP runs on almost any web server, on almost any platform. I have even built a web server in PHP which was capable of executing PHP scripts.
2) ASP natively supports only Access and MSSQL, whereas PHP natively supports a huge number of databases. They both support ODBC equally well. MySQL is a database that PHP closely integrates with; it is a very powerful database that rivals Oracle in speed. Like PHP, MySQL is free, and blows most other databases out of the water. Another hidden cost with ASP is the database angle; Microsoft expects you to develop using Access and when your webpage outgrows it, to switch to MSSQL, an extremely expensive option.
3) While even the best software has glitches, PHP has notoriously few. The PHP development team has an outstanding reputation for fixing bugs, and in order to streamline the process they even have an online system through which new bug reports can be submitted. Most bugs are resolved within 24 hours, and I'm speaking from experience here. There are a huge number of outstanding bugs in ASP which will probably never be fixed. Unless you're a major corporation, chances are that your bug report to Microsoft will likely go unanswered.
4) And finally, cost. PHP is free. ASP isn't free. If you want to use ASP, you have to use IIS, and if you want to use IIS, you have to buy Windows. Traditionally, the cost of Windows has been high. Microsoft has been aggressively trying to reduce this factor but they're hardly going to give Windows away for free. The cost of running an ASP-based website implies a full Windows server platform; development costs are higher, software licenses are expensive and speed, security and flexibility are all sacrificed.
There's a reason that Unix and Linux are dominant in the server market; money, security and performance all speak volumes.
Article by Neeraj Yadav, software evaluer.