See the Exadata vs Exalogic information updated for 2021 here.
Original 2012 post below:
Oracle Exadata (Oracle Exadata Database Machine) is strictly a data processing solution offered by Oracle. Initially conceived and promoted as a solution for mainly large data warehouse data load processing, Oracle now boldly proclaims that Exadata is suitable for high concurrency OLTP applications as well. It’s important to understand that Exadata isn’t something you use in addition to your current Oracle databases – rather, it comes with its own prepackaged Linux based Oracle database. Exadata is a prepackaged box that consists of the Oracle Exadata Storage Server software , Oracle Database 11g software, in addition to Sun branded hardware (RAM and CPUs) and Infiniband network technology software. Oracle’s claims of ultra fast data processing with Exadata are well supported by actual field experience of several companies, making this a really big success for Oracle Corporation. In addition to enabling fast processing of heavy amounts of data, Exadata also helps you consolidate multiple Oracle databases into a single easily manageable system. It’s important to note that the Exadata package (servers, software, network and storage) is completely preoptimized and preconfigured by Oracle.
If you’re running high volume, mission critical OLTP applications, or if you are having problems making sure that your current Oracle databases can crunch through heavy loads of warehouse data, it’s time to take a close look at Exadata – it’s more than likely that you’ll be surprised at the ease with which you can transition to Exadata from your current Oracle database based applications. Oracle claims that you’ll need fewer CPUs to run Exadata as compared to a non-Exadata solution. Exadata is configured in a balanced format, in units of “Racks” that are similar to standard data center rack configurations – you can purchase a quarter, half or a full rack and you can easily upgrade to more processing power by ordering additional Exadata racks.
Oracle Exalogic (Oracle Exadata Elastic Cloud) is also an “engineered system” and is similar to Exadata in the sense that it’s also a prepackaged hardware plus software solution, designed to be managed and monitored as a single stack. However, the main purpose of Exalogic isn’t data crunching – it’s an engineered system designed to provide high performance for Oracle middleware using custom Java EE applications, Oracle Applications and similar enterprise level applications.
Both Exadata and Exalogic are part of Oracle’s new paradigm of “purpose built systems” that provide pretested and preconfigured standardized sets of hardware, smart storage, and network and software components. The key goals are easy implementation, high speed processing and easy scalability on demand. The fundamental idea behind Oracle’s engineered systems – that standardizing and optimizing al the components will provide a higher performance through the exploitation of the synergies among the various components seems to be borne by the experience of users.