of the clock forward logic. Additionally, the framing clock can have a period that is less than, equal to, or greater than the time it takes to send a full four cycle command/ address.

GCLK

Global clock within the 21264/EV67.

granularity

A characteristic of storage systems that defines the amount of data that can be read and/ or written with a single instruction, or read and/or written independently.

hardware interrupt request (HIR)

An interrupt generated by a peripheral device.

high-impedance state

An electrical state of high resistance to current flow, which makes the device appear not physically connected to the circuit.

hit

See cache hit.

Icache

Instruction cache. A cache reserved for storage of instructions. One of the three areas of primary cache (located on the 21264/EV67) used to store instructions. The Icache con- tains 8KB of memory space. It is a direct-mapped cache. Icache blocks, or lines, con- tain 32 bytes of instruction stream data with associated tag as well as a 6-bit ASM field and an 8-bit branch history field per block. Icache does not contain hardware for main- taining cache coherency with memory and is unaffected by the invalidate bus.

IDU

A logic unit within the 21264/EV67 microprocessor that fetches, decodes, and issues instructions. It also controls the microprocessor pipeline.

IEEE Standard 754

A set of formats and operations that apply to floating-point numbers. The formats cover 32-, 64-, and 80-bit operand sizes.

IEEE Standard 1149.1

A standard for the Test Access Port and Boundary Scan Architecture used in board- level manufacturing test procedures.

Inf

Infinity.

INT nn

The term INTnn, where nn is one of 2, 4, 8, 16, 32, or 64, refers to a data field size of nn contiguous NATURALLY ALIGNED bytes. For example, INT4 refers to a NATU- RALLY ALIGNED longword.

Glossary–8

Alpha 21264/EV67 Hardware Reference Manual

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Compaq EV67, 21264 specifications Gclk, Idu