Glossary of PC Processors by x86.org

Glossary of PC Processors by x86.org


CISC=Complex Instruction Set Computer. A CISC microprocessor is one in which the number of bytes needed to represent the opcode instruction is not a fixed, regular length (for example, 32-bits each).

Opcode=The data that represents a microprocessor instruction.

RISC=Reduced Instruction Set Computer. A RISC microprocessor that has fewer, simpler instructions than its CISC counterpart. RISC instructions perform simple, rudimentary functions. The simplicity of these instructions results in a very simple microprocessor design that can execute very fast. RISC instructions are typically characterized by fix length instruction sets (for example, all instructions are 32-bits each).

EPIC=Explicitely Parallel Instruction Computing. EPIC is a fancy acronym that Intel invented to obfuscate the fact that they do not want the public appearance that their Merced microprocessor is actually a VLIW design. After all, Intel didn't invent VLIW, therefore they don't want to be publicly associated with a VLIW design.

VLIW=Very Long Instruction Word. A microprocessor that packs many simple RISC-like instructions into a much longer internal instruction word format. A VLIW microprocessor will usually have execution units, capable of executing all of the instructions contained in the instruction word, in parallel.

MMX=Multi-Media eXtensions. Intel claims that "MMX" is not an acronym, meaning "Multi-Media eXtensions" because they have filed for a trademark under this name. In reality, MMX instructions are intended to enhance programs that have multi-media capabilities.

Address Lines=The number of address lines, or "address pins" on a microprocessor determine how much memory the chip can address. The amount of addressible memory can be calculated as 2^#address_lines (two raised to the power of the number of address lines). A microprocessor with 32 address lines can address 232 bytes of memory (4 G Bytes).

Cache=A cache is a bank of high speed memory that stores the most recently accessed code and data. When the microprocessor requests data that is in the cache, the amount of time to retrieve the data is many times less than the amount of time needed to access main memory. Many microprocessors have a cache inside of the chip itself. In some cases, there is a cache for the cache (known as a 2nd-level cache). A cache may hold code, data, or even recently accessed data on a hard disk. In general, a cache can be created for faster access to any slower device, beit main memory or hard disks.