what is ASIC

Application-specific integrated circuits (ASICs) are semiconductor circuits specifically
designed to suit a customer’s particular requirement, as opposed to
DRAMs or microcontrollers, which are general-purpose parts.

The challenge of an ASIC flow is that typically the design is new and
specialized, and there is no previous history on which to base architectural
decisions. In this case there is significant emphasis on defining and verifying the
architecture of the design.
Another characteristic of ASICs is that the designs are heavily biased toward
logic structures. The design entry of this type of circuitry is tedious in a fullcustom
environment and not practical for designs exceeding 5,000 transistors.
HDL methodologies therefore are standard for these designs where transistors are
completely hidden from the designer.

In terms of layout, the picture is very similar. The layout designer is no
longer involved in transistor-level design and architecture, but in block-level
using advanced place-and-route tools. He may not actually see the full layout
view of the library because for place-and-route purposes the obstruction shades
are enough to generate complex blocks or chips.
Re: what is ASIC

Application specific integrated circuits (ASICs) are microelectronic integrated circuit (IC) chips that vary in degree of customizability. Application specific integrated circuits provide their users the ability to manufacture products having a proprietary design without having to begin the design at the device level. Many different ASIC technologies are available, including gate array, standard cell, full custom design, and programmable logic devices. The ASIC forms, in a single, semi-conductor substrate, the equivalent of several different integrated circuits each designed to perform one or more desired operations, such as a microprocessor operation, a memory operation, various interface operations (e.g., memory interface, processor interface), etc. ASIC operational blocks are typically designed to include thousands of individual logic gates necessary for performing the desired operation(s). These logic gates are formed in a substrate layer according to known semiconductor fabrication techniques. An application specific integrated circuit (ASIC) may include a semiconductor chip, wherein the chip includes memory devices such as random access memory (RAM). Examples of RAM devices include static random access memory (SRAM) and embedded dynamic random access memory (DRAM). A programmable application specific integrated circuit (ASIC) is a versatile integrated circuit chip, the internal circuitry of which may be configured before packaging by a manufacturer or after packaging by an individual user to realize a user-specific circuit. Application specific integrated circuits have become widespread in the semiconductor industry. ASICs (application specific integrated circuits) are widely used by electrical design engineers to include specialized circuitry in their designs using only a single chip.