But you know that a 1K byte memory has 1024 bytes - not 1000 bytes?

Strictly speaking, an uppercase has no meaning in the International System of Units ("SI Units") - so "1KHz" is just plain wrong.
The uppercase 'K' = 1024 is really just computing/digital electronics "slang"

The International System of Units ("SI Units") defines the lowercase 'k' to indicate a multiplier of 1000, and this was long established before the SI was formalised; eg, in kg, km, etc.

http://physics.nist.gov/cuu/Units/rules.html
http://www.npl.co.uk/npl/refer...tions.html

In fact, the usage of the lowercase 'k' was well-established long before digital electronics came along - which was why the uppercase 'K' was chosen to indicate a multiplier of 1024 (convenient for binary systems), being close to 1000, but a little larger.

It's easy to remember: a big 'K' (1024) is larger than a small 'k' (1024).

Unfortunately, disk drive marketing materials often deliberately confuse the issue...