When will RHEL 4 be 'outdated'
 

I'm installing some brand new RHEL servers, and am thinking about whether to use RHEL 4, 5, or 5.1. I don't install the GUIs, and don't expect to be using the clustering or virtualization facilities for at least another year or two, likely more. I have a few questions below that'll help me in making a decision.

Does it just make sense to go with RHEL 5.x because it's the newest version, or would I be paying performance and other penalties for newer, advanced features in RHEL 5.x that I wouldn't be using?

When will RHEL 4 be considered outdated (i.e. when should new RHEL servers absolutely use 5.x and not 4)?

For straight command-line usage, is there a lot of new learning to be done in the transition from 4 to 5.x, or is it a completely transparent transition? (e.g. any changes in the layout of files/directories, commands, options, etc?)

Which of the two versions do you recommend, and for what reasons?

Thanks.

1: One does not pay for the OS, one pays support. RHEL5 is (a tiny bit) faster over 4. Both have pretty much the same features. One should use the new OS because they have a need to support some hardware that is not supported by the older OS.

2:2012

3: No new learning it is a completely transparent transition.

4: RHEL5 update1 mainly for support for new hardware that is not supported by RHEL4 update6 (coming soon).

Thanks for your response.

Could you please elaborate on what is meant by one doesn't pay for the OS but for support? How can one get access to RHEL 4 or 5 - on the Red Hat website, the only thing that's available for download is a 30-day evaluation, and that can only be received after taking a sales call from a Red Hat representative. I can't use an evaluation version, but rather need a download of it that can be used as long as we'd like, and legally in production at a commercial business.

Yes one pays for support from Red Hat not the OS, one of the benefits for paying for this support is the ability to download the compiled binaries in rpm format or in ISO format (RHN subscription a part of the paid support). Red Hat does not have to provide the compiled rpms in any format. They do provide all the open sources as source RPMS. One can if desired download the all the open source packages and build;

ftp://ftp.redhat.com/pub/redhat/linux/

I noticed that your tag states your distribution is CentOS 4, this is basically the same thing as RHEL-4 without the "Red Hat branding and artwork" along with third party Supplementary packages are not included (your not missing much, all are available from third parties anyhow). You can use CentOS in a commercial business. CentOS is roughly equivalent to RHEL AS. Anything wrong with using CentOS-5 or very soon CentOS-5.1???

http://www.centos.org/modules/smartfaq/faq.php?faqid=31
http://www.centos.org/product.html

I see nothing here: https://www.redhat.com/apps/webform....e_form&eid=871 that states you need to speak to anyone from Red Hat before downloading the 30-day Evaluation version. The only things you will be missing are updates and support beyond the 30 days.