x86-64.net

General-purpose

RDSEED

RDSEED returns random numbers straight from the processor's hardware entropy source, meant for seeding software generators.

CPUID
RDSEED
CPUID.(EAX=07H,ECX=0):EBX[18]
Instructions
1 mnemonic
Processors
Broadwell, Skylake, Comet Lake, Cannon Lake, Ice Lake (client), Tiger Lake, Alder Lake, Arrow Lake, Panther Lake, Nova Lake, Skylake-SP, Cascade Lake, Cooper Lake, Ice Lake (server), Sapphire Rapids, Emerald Rapids, Granite Rapids, Diamond Rapids, Goldmont, Goldmont Plus, Tremont, Snow Ridge, Lakefield, Sierra Forest, Clearwater Forest, Knights Landing, Knights Mill, Zen, Zen+, Zen 2
Linux flag
rdseed

RDSEED returns bits from the processor’s non-deterministic generator (built to NIST SP 800-90B and SP 800-90C) rather than from the deterministic one that RDRAND reads. It is meant for seeding software random number generators. It too can run out of values when many cores ask at once: CF is then clear and the destination zero, and the caller retries a limited number of times.

RDSEED came with Intel’s Broadwell and AMD’s Zen.

Instructions

Mnemonics with at least one form in RDSEED. Each page lists all forms of the mnemonic, including those of other extensions.
MnemonicSummaryForms
RDSEEDReturns a random number straight from the processor's entropy source, to seed other generators; CF=1 means the value is valid, CF=0 that none was ready.1

CPUID and processors

XED splits RDSEED into 1 ISA set. Software can use a form when the processor reports every CPUID bit of one alternative of the form's ISA set.

XED ISA sets of RDSEED. Alternatives are separated by “or”; processors follow XED’s chip model, which covers AMD processors up to Zen 2.
ISA setCPUIDProcessors in XED
RDSEED

RDSEED
CPUID.(EAX=07H,ECX=0):EBX[18] RDSEED

Broadwell, Skylake, Comet Lake, Cannon Lake, Ice Lake (client), Tiger Lake, Alder Lake, Arrow Lake, Panther Lake, Nova Lake, Skylake-SP, Cascade Lake, Cooper Lake, Ice Lake (server), Sapphire Rapids, Emerald Rapids, Granite Rapids, Diamond Rapids, Goldmont, Goldmont Plus, Tremont, Snow Ridge, Lakefield, Sierra Forest, Clearwater Forest, Knights Landing, Knights Mill, Zen, Zen+, Zen 2

Sources

  1. Intel XED v2026.08.23 (commit 0bcb6237345c): forms, encodings, ISA sets, CPUID bits and chip model.
  2. Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 2 (325383-092, June 2026)
  3. Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 1 (253665-093, September 2026)

The tables are derived from Intel XED, Copyright Intel Corporation, licensed under the Apache License 2.0; x86-64.net converted and reformatted them. The text is our own.