The P55C (or 80503) was developed by Intel's Research & Development Center in Haifa, Israel. It was sold as Pentium with MMX Technology (usually just called Pentium MMX); although it was based on the P5 core, it featured a new set of 57 "MMX" instructions intended to improve performance on multimedia tasks, such as encoding and decoding digital media data. The Pentium MMX line was introduced on October 22, 1996, and released in January 1997. The new instructions worked on new data types: 64-bit packed vectors of either eight 8-bit integers, four 16-bit integers, two 32-bit integers, or one 64-bit integer. So, for example, the PADDUSB (Packed ADD Unsigned Saturated Byte) instruction adds two vectors, each containing eight 8-bit unsigned integers together, elementwise; each addition that would overflow saturates, yielding 255, the maximal unsigned value that can be represented in a byte. These rather specialized instructions generally require special coding by the programmer for them to be used. Other changes to the core include a 6-stage pipeline (vs. 5 on P5) with a return stack (first done on Cyrix 6x86) and better parallelism, an improved instruction decoder, 16KB L1 data cache + 16KB L1 instruction cache with Both 4-way associativity (vs. 8KB L1 Data/instruction with 2-way on P5), 4 write buffers that could now be used by either pipeline (vs. one corresponding to each pipeline on P5) and an improved branch predictor taken from the Pentium Pro, with a 512-entry buffer (vs. 256 on P5). It contained 4.5 million transistors and had an area of 140 mm2. It was fabricated in a 0.28 μm CMOS process with the same metal pitches as the previous 0.35 μm BiCMOS process, so Intel described it as "0.35 μm" because of its similar transistor density. The process has four levels of interconnect. While the P55C remained compatible with Socket 7, the voltage requirements for powering the chip differ from the standard Socket 7 specifications. Most motherboards manufactured for Socket 7 before the establishment of the P55C standard are not compliant with the dual voltage rail required for proper operation of this CPU (2.8 volt core voltage, 3.3 volt input/output (I/O) voltage). Intel addressed the issue with OverDrive upgrade kits that featured an interposer with its own voltage regulation. Tillamook Pentium MMX notebook CPUs used a mobile module that held the CPU. This module was a printed circuit board (PCB) with the CPU directly attached