Chronologically, the models of the family were:
HP 9810A, a keystroke programmable computer with magnetic cards and LED display, introduced in 1971,
HP 9820A, introduced in 1972, was the first HP model that deals with algebraic input (not only RPN) featured a high level language simpler than BASIC that was later named high performance language (HPL),
HP 9821A, similar to the HP 9820A, however, with Compact Cassette tape drive with clear leaders instead of using magnetic cards.
Tapes created on the HP 9821A could be read by the HP 9830A. Unlike later home computers which used standard cassette audio recorders which had to be manually put into record or play mode, it was completely controlled by software command, and could save and load to a file by number.

HP 9830A, introduced in 1972, was the top of the 9800 line, with the addition of a BASIC interpreter in read-only memory (ROM).
HP itself referred to it as a "calculator".

All 98x0 and 9821 systems used the same I/O interfaces.
A 400 line per minute 80-column thermal line printer was designed to fit on top of the 9820 and 9830.
Chronologically, the models of the family were:
HP 9810A, a keystroke programmable computer with magnetic cards and LED display, introduced in 1971,
HP 9820A, introduced in 1972, was the first HP model that deals with algebraic input (not only RPN) featured a high level language simpler than BASIC that was later named high performance language (HPL),
HP 9821A, similar to the HP 9820A, however, with Compact Cassette tape drive with clear leaders instead of using magnetic cards. Tapes created on the HP 9821A could be read by the HP 9830A. Unlike later home computers which used standard cassette audio recorders which had to be manually put into record or play mode, it was completely controlled by software command, and could save and load to a file by number.
HP 9830A, introduced in 1972, was the top of the 9800 line, with the addition of a BASIC interpreter in read-only memory (ROM). HP itself referred to it as a "calculator".
All 98x0 and 9821 systems used the same I/O interfaces. A 400 line per minute 80-column thermal line printer was designed to fit on top of the 9820 and 9830.
HP 9800 series