When customizing installation media, the base hardware system requirements recommendations may no longer be sufficient

Adding any files, hotfixes, language packs, drivers, etc. will increase the total size of files on the hard disk as well as increasing the size of the WIM files being modified, and affecting the memory footprint in WinPE, and the installed operating system.

Base system requirements will increase with any additions; however the exact requirements are not predictable as various customizations will interact. For example, when multiple language packs are installed, subsequent hotfixes may result in additional files on disk for each language. Compression technologies, such as the single instancing in the WIM file format can further complicate predicting the modified requirements. There are additional pressures on system memory requirements in the WinPE phase. When customizing images, it is recommended that you test low memory configurations with your customizations.

Additions to the boot WIM in particular will increase the WinPE RAM disk footprint. In WinPE, the scratch space is used by a variety of components as a temporary read/write location. Various customizations may increase scratch space usage, and larger scratch space configurations may compete for kernel mode memory. The default scratch space size is 32 MB.

As you add additional customizations to WinPE and your deployment images, the base system requirements will increase accordingly.

For additional information regarding how to determine available scratch space size:

http://technet.microsoft.com/en-us/library/hh824936.aspx

For additional information regarding WIM files:

http://technet.microsoft.com/en-us/library/cc749478(v=WS.10).aspx