"Early 486" comes from an uncited wikipedia table, added in
  https://en.wikipedia.org/w/index.php?title=CPUID&diff=prev&oldid=592047209
  https://en.wikipedia.org/w/index.php?title=CPUID&diff=prev&oldid=592047978
but I spot-checked the rest of the table accurate to CPUs in my house
(the oldest of which is an original Celeron, so no 486),
and "early 486" is better than "early x86" which can mean anything.

This does leave earlier x86 unmentioned,
but Linux hasn't targeted those in over a decade,
so they're out of scope anyway.

Signed-off-by: Ahelenia Ziemiańska <redacted>
---
 man4/cpuid.4 | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/man4/cpuid.4 b/man4/cpuid.4
index bd883e6d3..0b38fabe3 100644
--- a/man4/cpuid.4
+++ b/man4/cpuid.4

@@ -69,7 +69,9 @@ .SH NOTES
 There is no support for CPUID functions that require additional
 input registers.
 .P
-Very old x86 CPUs don't support CPUID.
+Early i486 CPUs do not support the CPUID instruction;
+.\" arch/x86/kernel/cpuid.c cpuid_open()
+opening this device for those CPUs fails with EIO.
 .SH SEE ALSO
 .BR cpuid (1)
 .P

-- 
2.39.2