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For example, a processor with 65,536 bytes of cache memory might be said to have "64 K" of cache. In this convention, one thousand and twenty-four kilobytes (1024 KB) is equal to one megabyte (1 MB), where 1 MB is 1024 2 bytes.
An alternative system of nomenclature for the same units (referred to here as the customary convention), in which 1 kilobyte (KB) is equal to 1,024 bytes, [38] [39] [40] 1 megabyte (MB) is equal to 1024 2 bytes and 1 gigabyte (GB) is equal to 1024 3 bytes is mentioned by a 1990s JEDEC standard. Only the first three multiples (up to GB) are ...
1 bit – 0 or 1, false or true, Low or High (a.k.a. unibit) 1.442695 bits (log 2 e) – approximate size of a nat (a unit of information based on natural logarithms) 1.5849625 bits (log 2 3) – approximate size of a trit (a base-3 digit) 2 1: 2 bits – a crumb (a.k.a. dibit) enough to uniquely identify one base pair of DNA
These prefixes are more often used for multiples of bytes, as in kilobyte (1 kB = 8000 bit), megabyte (1 MB = 8 000 000 bit), and gigabyte (1 GB = 8 000 000 000 bit). However, for technical reasons, the capacities of computer memories and some storage units are often multiples of some large power of two, such as 2 28 = 268 435 456 bytes.
In this convention, one thousand and twenty-four megabytes (1024 MB) is equal to one gigabyte (1 GB), where 1 GB is 1024 3 bytes (i.e., 1 GiB). Mixed 1 MB = 1 024 000 bytes (= 1000×1024 B) is the definition used to describe the formatted capacity of the 1.44 MB 3.5-inch HD floppy disk , which actually has a capacity of 1 474 560 bytes .
The 5.25-inch diskette sold with the IBM PC AT could hold 1200 × 1024 = 1 228 800 bytes, and thus was marketed as "1200 KB" with the binary sense of "KB". [40] However, the capacity was also quoted "1.2 MB", [ 41 ] which was a hybrid decimal and binary notation, since the "M" meant 1000 × 1024.
The Intel 8080 used by these computers was an 8-bit processor, with 16-bit address space, which allowed it access up to 64 KB of memory; .COM executables used with CP/M have a maximum size of 64 KB due to this, as do those used by DOS operating systems for 16-bit microprocessors.
This could be used to advantage if the programs were repeatedly loaded in different orders, and checking to see how much memory was free after each permutation. For example, if there was a 50 KB UMB and a 10 KB UMB, and programs needing 8 KB and 45 KB were loaded, the 8 KB might go into the 50 KB UMB, preventing the second from loading.