What is Proxy means

In computer networks, a proxy server is a server, that could be a computer system or an application program that acts as a go-between for requests from clients seeking resources from other servers. In other word, proxy server called man in the midle between real server on internet and the client. Simple work from a proxy server, client connects to server, requesting some service, such as a file, connection, web page, or other resource, available from a different server that allocate on other network. The proxy server evaluates the request according to its filtering rules. For example, it may filter traffic by protocol, time access, or IP address. If the request is validated by the filter, the proxy provides the resource by connecting to the relevant server and requesting the service on behalf of the client. A proxy server may optionally alter the client's request or the server's response, and sometimes it may serve the request without contacting the specified server. In this case, it 'caches' responses from the remote server, and returns subsequent requests for the same content directly. With this use, our connection to internet will be more simple because we didn't need to contact the real server to have what we want. We can set our proxy server to update the data to synchronous with the real server.
A proxy server has two main purposes:

• To keep machines behind it anonymous. It's really help us to keep our privacy and network security.
  
• To speed up access to a resource (via caching). It is commonly used to cache web pages from a web server.

A proxy server that passes requests and replies unmodified is usually called a gateway or sometimes tunneling proxy. A proxy server can be placed in the user's local computer or at various points between the user and the destination servers or the Internet. A reverse proxy is a proxy used as a front-end to accelerate and cache in-demand resources (such as a web page).

Collaboration between Facebook with Twitter

We all know Facebook is a most growth social networking in internet. It's connect so many people so easily and make a distance has no meaning. Also with Twitter, this is a mini blog with high growing rate as well as Facebook does. Now we will make a collaboration between this two powerfull site. We will make an update from Facebook will be appear in our Twitter homepage and vice versa.

1. Facebook make an update to Twitter
   First, find your status RSS feed on Facebook. It is buried. To find it, we need to visit our profile and on our mini-feed select "See All". On the right you will see a list of items, select “status stories” and finally below this a feed link can be found. Finally add your newly found status RSS feed to the TwitterFeed service. In this step, we can set our update frequentcy, prefixed it with "From Facebook..." and am publishing just the title from the status feed.
2. Twitter make an update to Facebook
   The official Twitter Facebook app (found here: http://apps.facebook.com/twitter/) has an option after you install it to update your Facebook status with your latest tweet. We need to understand that there is a delay if you use twitter frequently. But overall it's really powerfull to make frequently update for both with one update in a side.
   

Both Facebook and Twitter have pretty extensive APIs that you can develop applications against. With these a lot is certainly possible, but it would take development time and effort to write the code necessary to accomplish whatever else you might want to do. Also keep in mind that "everything" isn't possible. The APIs are limited in certain respects, specially where privacy, technical, or other issues might be involved.

What is set associative mapping

set associative cache - A compromise between a direct mapped cache and a fully associative cache where each address is mapped to a certain set of cache locations. The address space is divided into blocks of 2^m bytes (the cache line size), discarding the bottom m address bits. An "n-way set associative" cache with S sets has n cache locations in each set. Block b is mapped to set "b mod S" and may be stored in any of the n locations in that set with its upper address bits as a tag. To determine whether block b is in the cache, set "b mod S" is searched associatively for the tag.A direct mapped cache could be described as "one-way set associative", i.e. one location in each set whereas a fully associative cache is N-way associative (where N is the total number of blocks in the cache). Performance studies have shown that it is generally more effective to increase the number of entries rather than associativity and that 2- to 16-way set associative caches perform almost as well as fully associative caches at little extra cost over direct mapping.

source : http://encyclopedia2.thefreedictionary.com/set+associative+cache