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2003/10/29 block


© October 2003 Tony Lawrence

A Disk block, block of code, or blocking a program or process from proceeding.

The size of a disk block can cause confusion: "du" historically returned 512 byte blocks, as did "df", but now either or both may report 1024 byte blocks.

A code block is some logical unit, though it may have a specific definition (as it does in Perl). A programmer may casually refer to a "block of code" and that could mean anything from a subroutine to an entire module, but in more precise contexts it will be explicitly delimited.

A process can be blocked waiting for input or for some device to become ready. If that situation cannot happen because two or more processes are each waiting for the other to do something, you have a deadlock.


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"The size of a disk block can cause confusion: 'du' historically returned 512 byte blocks, as did 'df', but now either or both may report 1024 byte blocks."

Unless a hard drive is formatted with nonstandard values, a physical block will be 512 bytes. A UNIX logical disk block is 1024 bytes, a value that was picked years ago because the drives in the early PDP minis used 1K physical blocks. Incidentally, the associated filesystem structure was (and still is) referred to as S51K, meaning System V (5), 1 KB logical block size.

--BigDumbDinosaur



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