These are generally defined as a lower-level physical description that is specific to a particular process technology. Hard cores usually offer better predictability of chip timing performance and area for their particular technology. Analog and mixed-signal logic are generally distributed as hard cores. Hence, analog IP (SerDes, PLLs, DAC, ADC, PHYs, etc.) are provided to chip makers in transistor-layout format (such as GDSII). Digital IP cores are sometimes offered in layout format as well. Low-level transistor layouts must obey the target foundry's process design rules. Therefore, hard cores delivered for one foundry's process cannot be easily ported to a different process or foundry. Merchant foundry operators (such as IBM, Fujitsu, Samsung, TI, etc.) offer various hard-macro IP functions built for their own foundry processes, helping to ensure customer lock-in. Sources of IP cores Licensed functionality Many of the best known IP cores are soft microprocessor designs. Their instruction sets vary from small 8-bit processors, such as the 8051 and PIC, to 32-bit and 64-bit processors such as the ARM architectures or RISC-V architectures. Such processors form the "brains" of many embedded systems. They are usually RISC instruction sets rather than CISC instruction sets like x86 because less logic is required. Therefore, designs are smaller. Further, x86 leaders Intel and AMD heavily protect their processor designs' intellectual property and don't use this business model for their x86-64 lines of microprocessors. IP cores are also licensed for various peripheral controllers such as for PCI Express, SDRAM, Ethernet, LCD display, AC'97 audio, and USB. Many of those interfaces require both digital logic and analog IP cores to drive and receive high speed, high voltage, or high impedance signals outside of the chip. "Hardwired" (as opposed to software programmable soft microprocessors described above) digital logic IP cores are also licensed for fixed functions such as MP3 audio decode, 3D GPU, digital video encode/decode, and other DSP functions such as FFT, DCT, or Viterbi coding. Vendors IP core developers and licensors range in size from individuals to multi-billion-dollar corporations. Developers, as well as their chip-making customers, are located throughout the world. Silicon Intellectual Property (SIP, Silicon IP) is a business model for a semiconductor company where it licenses its technology to a customer as intellectual property. A company with such a business model is a fabless semiconductor company, which doesn't provide physical chips to its customers but merely facilitates the customer's development of chips by