Throughout my technological lifetime I followed the convention that 1 kB was equal to 1000 bytes and that 1 KB was equal to 1024 bytes. Similarly, 1 mB was 1 000 000 bytes, and 1 MB was 1 048 576 bytes.
In dial-up Internet days, we surmised that a 56K modem transferred data at a rate of 56 000 bits per second (that is, 56 kbps or 5.6 kBps). Therefore, dividing the nominal modem speed by 10 gave a simple divisor for quickly calculating the download times of files with sizes expressed in kB, that is,
download time in seconds = file size in kB / modem speed in kBps
In reality, however, this was no more than a loose convention adopted by Internet users to express data volumes and bandwidths, and distinguishing between 1000 bytes and 1024 bytes by using kB and KB in writing was very convenient.
I continued with this convention until comments from a heated debate on reddit informed me of the 1999 IEC 60027-2 standard, which introduced the kibi and removed all ambiguity. The MB Confusion blog post explains this standard in a more interesting way than the Wikipedia article.