It wasn’t just marketing. Historically, a kilobyte was 1024 bytes in memory contexts where everything was based on powers of two but nowhere else. This was obviously confusing because everywhere else used kilo as 1000 — a 420MB hard drive would have been measured in units of 1024 for capacity and 1000 for transfer speed.
When the SI units were standardized in 1998, it helped drive manufacturers advertise larger numbers but it also rectified this accident of history where a standard prefix had been used with a non-standard definition in only one part of computing.
When the SI units were standardized in 1998, it helped drive manufacturers advertise larger numbers but it also rectified this accident of history where a standard prefix had been used with a non-standard definition in only one part of computing.