So I’ve been talking wit heaps of folks on the RD list and a few blogs about http://www.getrpo.com and a question that commonly comes up is why not save yourself the $749 and just turn on IIS caching and compression… Here is my more long winded answer

So the compression and caching features in RPO are really more nice to haves and not core to the product. They’re mainly there for IIS6 users because getting those things working in IIS6 is a real PITA.

The big reason you want RPO is the combination stuff.

Basically the way it makes a big difference is by dramatically reducing the number of requests a browser makes over the wire. Request count * latency = performance killer.

So it combines the following sorts of things

1. Combines Javascript files
So for example you might have the following references to external JS
ElegantlyFactoredStringFunctions.js
MarvelousThridPartyJQueryLibraryThatIReallyDoNotWantToMessWith.js
CrazyJavascriptEmmitedByAThirdPartyControlForWhichIHaveNoSourceAccessWhatSoEver.js
ObscureCustomerSpecificJavascriptThatIOnlyIncludeWhenTheHostHeaderContainsXXX.js
RPO will combine them all and insert into the page a link something like
http://www.syringe.net.nz/rpo.axd/20080530/6VD6JDaDtYSXH5FDASYvrg (this link may change over time, just view the page source of use Firebug to get the idea)

2. Combines CSS files
Again, same thing applies as with the *.JS file.
You do need to be a little careful with choosing files to exclude to ensure you don’t end up regenerating a completely new combined file for each page.
So for example if you had 5 *.css files common across your whole site and then each page had a page specific CSS file then you’d want to exclude the page specific ones. It would be neat f the RPO guys could maybe support a namespace for use with XHTML that would let you chunk resources into groups e.g.
<link rel="stylesheet" type="text/css" href="site-common-general.css" rpo:group=”0”/>
<link rel="stylesheet" type="text/css" href="site-common-menus.css" rpo:group=”0”/>
<link rel="stylesheet" type="text/css" href="page-specific-user-form.css" rpo:group=”1”/>
<link rel="stylesheet" type="text/css" href="page-specific-custom-rollovers.css" rpo:group=”1”/>

They’d default any non attributed link tags to group 0. This approach would mean that for those willing to appl a little extra effort t design time they still get excellent combination AND caching support at runtime without ending up resending the site common CSS combined with the page specific CSS for every page request.

3. Does funky combination of images in one of two ways

a. Either tiles the images using CSS Sprites http://www.alistapart.com/articles/sprites/ or;

b.  Inlines the images using CSS http://stevesouders.com/hpws/inline-css-images.php

To give you an example for the images

http://www.syringe.net.nz is my blog site

The following is the link to the large tiled JPEG that represents all the JPEG images on the page

http://www.syringe.net.nz/rpo.axd/20080530/6VD6JDaDtYSXH5FDASYvrg

and all the GIFs

http://www.syringe.net.nz/rpo.axd/20080530/$-jsx07uuSjpOAX$WsgU$w

Basically RPO has parsed the HTML, found all the images, retrieved all the images, created a tiled JPEG, cached the tiled image data, injected CSS code back into the HTML to chop them up on the client side.