Alternative PHP Cache (APC)

Alternative PHP Cache (APC)

APC is an Open Source PHP accelerator for caching intermediate code from scripts. Intermediate code is the internal memory structures produced during compilation that are fed into the executor. APC increases the performance of PHP scripts by caching them in their compiled state, so that the overhead of compiling is almost completely eliminated. APC stores and executes compiled PHP scripts from shared memory.

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DomainKeys Identified Mail (DKIM)

DomainKeys Identified Mail (DKIM) is basically used for E-mail authentication. The aim of domain keys is to detect whether emails come from their claimed domain. DomainKeys is a rapidly emerging Internet standard mainly used by Yahoo Mail as well as Gmail. Yahoo has even acquired the patents (U.S. Patent 6,986,049) for DomainKeys. Compared to the normal method of email authentication, Domain Keys offers almost end-to-end integrity from a signing Mail Transfer Agent (MTA) to a verifying MTA. The basic working of Domain Keys can be summarized as follows:
The signing MTA will insert a header named DomainKey-Signature that contains a digital signature of the contents of the mail message. The common authentication mechanism is to use SHA-1 as the cryptographic hash and RSA as the public key encryption scheme, encrypted hash is encoded using base64. After that the signature validation is done by retrieving the senders public key through the DNS. That is the receiving SMTP server uses the name of the domain from which the mail originated, the string _domainkey, and a selector from the header to perform a DNS lookup. The returned data will include the domains public key. The receiver can then decrypt the hash value in the header field and at the same time recalculate the hash value for the mail body that was received, from the point immediately following the DomainKey-Signature header. If the two values match, this cryptographically verifies that the email originated at the correct domain and has not been tampered with in transit. DomainKeys is independent of Simple Mail Transfer Protocol (SMTP) outing aspects which uses the transported mail data, header and message body.

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DHCP (Dynamic Host Control Configuration Protocol)

Dynamic Host Configuration Protocol (DHCP) is a network protocol that enables a DHCP server to automatically assign an IP address to an individual computers TCP/IP stack software. DHCP assigns a number dynamically from a defined range of numbers configured for a given network. Continue reading…

VPS : Virtual Private Server

What is a Virtual Private Server?

A Virtual Private Server (VPS) is an entire operating system that runs within another operating system. It will share system resources like the CPU and RAM with other users but the resources are allocated in such a way that you cannot tell that the system has anyone else on it, much like a dedicated server. So resources are usually setup in such a way that each hosting client is only allowed to use an allocated percent, meaning that resources assigned to you will always available to you. Each virtual server looks and acts like a dedicated server.
So for instance, there may be a server with 2GB RAM, 100GB of disk space and 2 x 2GHz processors with 10 VPSes on it. Each one is guaranteed to have access to 200MB RAM, a disk space limit of 10GB, and an effective CPU of 400Mhz.

There are a number of virtualization technologies, which make this all possible. There are commercial companies such as VMWare, XEN.

Like an emulator, VMware software provides a completely virtualized set of hardware to the guest operating system. VMware software virtualizes the hardware for a video adapter, a network adapter, and hard disk adapters. The host provides pass-through drivers for guest USB, serial, and parallel devices.

In essence, virtualization lets you transform hardware into software. Use software such as VMware ESX Server to transform or virtualize the hardware resources of an x86-based computerincluding the CPU, RAM, hard disk and network controllerto create a fully functional virtual machine that can run its own operating system and applications just like a real computer.

Multiple virtual machines share hardware resources without interfering with each other so that you can safely run several operating systems and applications at the same time on a single computer.

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