Talk:Fragmentation (computing)

Internal Fragmentation

I recently reverted an edit that turned the Internal Fragmentation section into the text below. This text might have some useful contributions, but it's nowhere near good enough to replace the existing text yet.

Allocation either including reduntant information or data which are not going to be used. The term "internal" means that the unusable storage is inside the allocated region but is not being used.

Purpose and advantages:

• Usually provides increased efficiency or simplicity.

Disadvantages:

• More difficult to reclaim than other forms of fragmentation.
  • Usually the best way to remove it is with a design change. For example, in dynamic memory allocation, memory pools drastically cut internal fragmentation by spreading the space overhead over a larger number of objects.

Examples:

• In many file systems, files always start at the beginning of a sector (simplifies organization, easier growth of files). Any space left over between the last byte of the file and the first byte of the next sector is a form of internal fragmentation called file slack or slack space.
• Examples of use of metadata:
  • Program allocates a single byte of data is often allocated many additional bytes for metadata and alignment.
• Examples of use of reserved (often unused) resources:
  • IP addresses can only be reserved in blocks of certain sizes (thus many IPs are reserved but not actively used). This is contributing to the IPv4 address shortage.
  • English text is often stored with one character in each 8-bit byte. Although in standard ASCII encoding the most significant bit of each byte is always zero.