'what does "outb" in AT&T asm mean?

I am reading some code of Linux. The keyboard.S has something like

outb %al,$0x61

and

inb $0x61,%al

I think the pending 'b' means 'byte', but i still cannot find what these instructions mean.

Solution 1:^[1]

Yes, the out port and in port instructions can be encoded for 8 bits of data or 16 bits of data. The b indicates byte which is the 8 bit version.

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Solution	Source
Solution 1	old_timer