HDL

HDL is an acronym that can refer to more than one field. The two most common meanings are high-density lipoprotein, a class of lipoproteins in the blood, and hardware description language, a family of languages used to model digital circuits.

High-density lipoprotein (HDL) is a class of lipoproteins that transports lipids in the bloodstream. HDL is relatively small and protein-rich, with apolipoprotein A-I as a major component. It participates in reverse cholesterol transport, collecting cholesterol from peripheral tissues and delivering it to the liver for excretion or reuse. Higher HDL-C levels are associated with a lower risk of atherosclerotic cardiovascular disease, while low HDL-C is a recognized risk factor. HDL-C is measured in milligrams per deciliter (mg/dL); commonly, levels below 40 mg/dL in men and below 50 mg/dL in women are considered low, and levels of 60 mg/dL or higher are regarded as protective. HDL particles are heterogeneous, including HDL2 and HDL3 subtypes. Lifestyle factors such as aerobic exercise, a healthy diet, and weight management can raise HDL-C, while genetics and certain diseases can lower it.

Hardware description language (HDL) refers to languages used to model, simulate, and often synthesize digital circuits. The main examples are VHDL and Verilog, with SystemVerilog adding extended verification features. An HDL describes circuit structure (structural), behavior (dataflow or behavioral), and timing. Designs are simulated to verify function before being synthesized into hardware for FPGAs or ASICs. Typical workflows include specification, modeling, simulation, synthesis, timing analysis, and verification with test benches. HDLs emphasize concurrency and time, reflecting hardware parallelism, and provide constructs for signals, components, and modules, enabling precise, repeatable hardware implementation.