The POWER5 is a microprocessor

Microprocessor

A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...

 developed and fabricated by IBM

IBM

International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...

. It is an improved version of the highly successful POWER4

POWER4

The POWER4 is a microprocessor developed by International Business Machines that implemented the 64-bit PowerPC and PowerPC AS instruction set architectures. Released in 2001, the POWER4 succeeded the POWER3 and RS64 microprocessors, and was used in RS/6000 and AS/400 computers, ending a separate...

. The principal improvements are support for simultaneous multithreading

Simultaneous multithreading

Simultaneous multithreading, often abbreviated as SMT, is a technique for improving the overall efficiency of superscalar CPUs with hardware multithreading...

 (SMT) and an on-die memory controller

Memory controller

The memory controller is a digital circuit which manages the flow of data going to and from the main memory. It can be a separate chip or integrated into another chip, such as on the die of a microprocessor...

. The POWER5 is a dual-core microprocessor, with each core supporting one physical thread

Thread (computer science)

In computer science, a thread of execution is the smallest unit of processing that can be scheduled by an operating system. The implementation of threads and processes differs from one operating system to another, but in most cases, a thread is contained inside a process...

 and two logical threads, for a total of two physical threads and four logical threads.
Technical details of the microprocessor were first presented at the 2003 Hot Chips

Hot Chips

Hot Chips is an IEEE sponsored technological symposium which is held every year in August on Stanford University campus since 1989. The general emphasis of the conference are microprocessors and integrated circuits. Processor makers often announce details about future processor designs at the...

 conference.