THE CARRY FLAG the one bit the sum could not hold — saved in a status register
When an 8-bit add overflows — 200+100=300, but only 44 fits in a byte — the missing high bit is not lost. It is caught in the carry flag, a single bit in the processor's status register. That flag is how a machine adds numbers wider than its word: add the low bytes, keep the carry, feed it into the high bytes (add-with-carry). It is also the unsigned overflow signal — “the result did not fit.” The carry, having rippled off the top of the adder, is saved for the next instruction — the thread's carry, made an architectural fact.
THE TECHNIQUE carry flag = the bit that overflowed the word; enables multi-word add
The demo adds 200+100 in 8 bits — the result wraps to 44 and the carry flag is set: live demo
HISTORY & CREDIT the status register carry bit
“An 8-bit add that overflows loses the top.” — it is caught in the carry flag and fed to the next byte; that flag is how a machine adds numbers wider than itself. cited
the flag · the carry-out of the top bit, latched in the status register (C). add-with-carry · low bytes first, then high bytes plus the saved C — arbitrary-width addition. unsigned overflow · C set means “did not fit” for unsigned numbers (V is the signed version, dart 382).
The bit the byte could not hold, latched and handed to the next instruction — the carry, promoted to architecture. the carry flag
RECOMMEND FOR I-13 the overflow bit, on the compiler
On the canonical compiler, 200+100=300; the byte holds 44 and the carry flag is set (300≥256):
$ i13 run c_carryflag.i13 # 8-bit add overflow
RUN OK · 18 step(s) · peak stack 2 · call depth 0
sum = 300 result = 44 -- 300 mod 256
set = 1 -- carry flag: the high bit that did not fit
Recommend: the carry flag is the thread's carry become an architectural fact — the one bit a word cannot hold, latched for the next instruction, and the way a machine adds beyond its width — and i13 sets it on 200+100. Not a keeper (a status bit that reports overflow is a recognizer — it witnesses “did not fit,” per B41). The dart that makes the carry persist across instructions.