It's interesting to note that it wasn't always like that. IBM mainframes had a thing called "CKD", which stands for "count, key, data": https://en.wikipedia.org

It's interesting to note that it wasn't always like that. IBM mainframes had a thing called "CKD", which stands for "count, key, data": https://en.wikipedia.org/wiki/Count_key_data https://en.wikipedia.org/wiki/Count_key_data In this scheme, you'd ask the hard disk[1] not for the bits/byte/word at a given position, but actually for a key associated with a record. The hardware would then give you the variable length record associated with that key back. Now you may argue, "yes, but the data on that disk/DASD was, on a low level, still an array of bits". And... well, sort of. I don't know the full details[2], but it looks like the records were separated similarly to how nowadays sectors are separated on modern (spinny) hard disks: By "gaps". Those are technically also bits, but they are recognized by lower level hardware and abstracted away from what reaches the "computer". Nowadays, CKD is still supported, but merely emulated on pretty boring commodity disks (sorry, "DASDs") that are addressed using sectors and tracks (or actually just sector number, since we started abstracting actual disk geometry away a few decades ago), arranged in a rigid sequential order. [1] Aside, IBM calls a hard disk "DASD": direct-access storage device. [2] The full details are here: https://web.archive.org/web/20200330172847/http://bitsavers.org/pdf/ibm/dasd/2314/A26-3599-4_2314_Sep69.pdf https://web.archive.org/web/20200330172847/http://bitsavers....