You must know Magento 2.0.x system requirements before installation

If you are in process of installing the Magento 2.0.x then I strickly reccommned you to check following Magento 2.0.x system requirements before installation.

You need to confirm following items on your server system or local system:
#Operating systems (Linux x86-64)
#Web servers
#Database
#PHP
#Required PHP extensions
#PHP OPcache
#PHP settings
#SSL
#Mail server
#Optional but recommended php_xdebug2.2.0

Lets have a look at all the above items in detail:

#Operating systems (Linux x86-64)

Linux distributions such as RedHat Enterprise Linux (RHEL), CentOS, Ubuntu, Debian, and so on
Memory requirement

Upgrading the Magento applications and extensions you obtain from Magento Marketplaces and other sources can require up to 2GB of RAM. If you are using a system with less than 2GB of RAM, we recommend you create a swap file; otherwise, your upgrade might fail.
Composer (latest stable version)

Composer is required for developers who wish to contribute to the Magento 2 codebase or anyone who wishes to develop Magento extensions

#Web servers::
    - Apache 2.2 or 2.4
    - In addition, the apache mod_rewrite module must be enabled. mod_rewrite enables the server to perform URL rewriting. For more information, see our Apache documentation.
    - nginx 1.8 (or latest mainline version)

#Database::
- MySQL 5.6
- MariaDB and Percona are compatible with Magento because we support MySQL 5.6 APIs.

#PHP::
    - 5.6.x
    - 5.5.x, where x is 22 or greater
    - 7.0.2, 7.0.6–7.0.x
    There is a known PHP 7.0.5 issue that affects our code compiler; to avoid the issue, do not use PHP 7.0.5.

    Not supported:
        - PHP 7.1
        - PHP 5.4

#Required PHP extensions::
    - bc-math
    - curl
    - gd, ImageMagick 6.3.7 (or later) or both
    - intl
    - mbstring
    - mcrypt
    - mhash
    - openssl
    - PDO/MySQL
    - SimpleXML
    - soap
    - xml
    - xsl
    - zip
    PHP 7 only::
        - json
        - iconv

#PHP OPcache::
We strongly recommend you verify the PHP OPcache is enabled for performance reasons. The OPcache is enabled in many PHP distributions. To verify if it is installed, see our PHP documentation for CentOS or Ubuntu.

#PHP settings::
We recommend particular PHP configuration settings, such as memory_limit, that can avoid common problems when using Magento.

#SSL::
    - A valid security certificate is required for HTTPS.
    Self-signed SSL certificates are not supported.
    - Transport Layer Security (TLS) requirement
    - PayPal and repo.magento.com both require TLS 1.1 or later

#Mail server::
- Mail Transfer Agent (MTA) or an SMTP server
- Magento can utilize the following technologies:

    Redis version 3.0 for page caching and session storage (the latter supported by Magento version 2.0.6 and later only)
    Varnish version 3.5 or latest stable 4.x version for page caching

    memcached latest stable version for session storage with either memcache or memcached PHP extensions (latest stable version)

    Magento Enterprise Edition (EE) only::
        - Apache Solr 4.x
        - Solr search can be used as a search provider. Available for Magento Enterprise Edition (EE) only.
        - RabbitMQ 3.5
        - RabbitMQ can be used to publish messages to queue and to define the consumers that receive the messages asynchronously. Available for Magento EE only.

        Three master databases::
        - These master databases provide scalability advantages for different functional areas of the Magento application: checkout, orders, and product data. Available for Magento EE only.

#Optional but recommended php_xdebug2.2.0::
    - php_xdebug2.2.0 or later (development environments only; can have an adverse effect on performance)


The major differences between Magento 2.0.x and Magento 2.1.x: #PHP - Dropped support for PHP 5.5.x - 2.1.2 and later: Added support for PHP 7.0.4 #MySQL (2.1.2 and later): - Compatible with MySQL 5.7 #Added support for Elasticsearch 1.7 and 2.x (recommended by Magento) - If you get the Elasticsearch software from the Elasticsearch Linux repository, Magento support versions 2.x. - If you get the Elasticsearch software from their Elasticsearch-PHP repository, Magento support the 2.0 branch.

I would like to thanks to Magento community who provided a fantastic documetation.
Reference Magento Site: http://devdocs.magento.com/guides/v2.0/install-gde/system-requirements-tech.html