How do you know how many mb is in kb?

On computers in most places a kilobite is 2^10 and a megabite is 2^20.

One exception is the way hard disk manufacturers advertise disk size. When they say megabite to mean 10^6 rather than 2^20 bytes. Likewise they also consider a gigabite to be 10^9 bytes and a terabyte to be 10^12 bytes. Many people feel the way hard disk makers advertise quantity is misleading and there was even a class action lawsuit against hard drive manufactgurers but I don’t know what ever became of it. In places where the power of 2 and the power of 10 quantities can be confused it is best to use a small ‘m’ for power of 10 and a large ‘M’ for power of 2.

Byte is also a problem. We think of bytes as 8 bits but they aren’t necessarily so. Throughout computer history bytes have been diffferent sizes because some computers has smaller or larger character sets. The highly influencial IBM 360 mainframe set the byte at 8 bits and when microcomputers came on the scene they also used 8 bits. Now we need more than 8 bits for extended character sets so we end up using multibyte characters. Perhaps we would have been better off using a longer word but it would be rather difficult to change at this point. When I did some consulting work with the US Navy they avoided the term byte and used octet for 8 bit quantities. Ironically they still called a 4 bit quantity a nibble instead of a quartet but as far as I know nibble has never been used to describe anything but 4 bits. I suppose if we used 10 bit bytes we could have 5 bit nibbles but I digress.

An other problem is if you mean bit or byte. Network people talk about throughput in terms of bits while comuter people usually talk in terms of bytes. On a network we have T1s that have 1.5 megabits/second of bandwidth while on a hardrive we might write 20 megabytes/second of throughput. To distinguish between bits and bytes in abreviations we usually use a small ‘b’ for bits and a large ‘B’ for bytes.

So one would assume

kb=10^3 bits kB=10^3 bytes Kb=2^10 bits KB=2^10 bytes mb=10^6 bits mB=10^6 bytes Mb=2^20 bits MB=2^20 bytes

Since you are asking about 1440 I assume you are refering to the old 3.5” floppy. They are generally refered to as 1.44 MB floppies but they really aren’t. The 1.44 MB floppy had 2 sides, 80 tracks, 18 sectors/track, and 512 bytes/sector. This comes out to 1474560 bytes. If we divide that by 10^6 we get 1.48 mB; if we divide that by 2^20 ro 1048576 we get 1.41 MB. Also, you don’t get all that space to use. The operating system needs to put a directory and other information on the disk so the formatted (useable) capacity is a little less.