ASCII

American Standard Code for Information Interchange

Binary can store numbers. ASCII was an agreement about what some of those numbers should mean.

ASCII is a shared codebook.

Try a character. Watch the number and bits change.

Character

CharacterA

→

ASCII number65

→

7-bit ASCII1000001

→

Shown in 1 byte01000001

ASCII originally used 7 bits, which gives 128 possible codes. On these pages we show the value inside an 8-bit byte, so a leading 0 is added.

Computers needed a shared code so different machines could exchange text and agree that the same number meant the same character.

BEFORE ASCII

Computer makers used different character codes. Moving text between systems could mean translating from one code to another.

1963

ASCII became ASA standard X3.4. It used 7 bits, giving 128 possible codes for letters, numbers, punctuation, and control instructions.

1967–1968

Revisions refined the standard. ASCII became a common way for computers and communication equipment to exchange text.

A→65→01000001

Every box is one code from 0 to 127. Click one to inspect it — or use the hunt to learn where things live.

ASCII Hunt

Find the uppercase letter A.

Click the matching box in the table.

0 / 5

symbols / controls numbers uppercase lowercase

Click a group to highlight it in the table. Uppercase and lowercase versions of the same English letter are 32 apart: A = 65, a = 97.