Interesting to note that legacy mainframe sorting isn't just moving values around in memory like all the algorithms we mostly study today. Mainframes back then

Interesting to note that legacy mainframe sorting isn't just moving values around in memory like all the algorithms we mostly study today. Mainframes back then had vanishingly small amounts of RAM (compared to what we have today) and had to use tape and later disk (dasd) for any real storage. So this type of sort is known as disk or tape sort. One "nicety" was that most records on tape (and subsequently disk) were "fixed" length, so could count on advancing x number of bytes reliably for next/prev record etc. It was a different era for sure.