Later a less capable aircraft, the Curtiss P-40 arrived and trainees split their time of both aircraft . On 1 May 1944 the 53d Fighter Group was inactivated and replaced by the Page Replacement Training Unit ( PRTU ), which was part of an administrative change by Third Air Force to streamline the organization of the base.
22.
With this solution, practically without added cost, in almost all the cases, and particularly for instructions and sequential data strings, the addressing is performed in physical mode but without need to wait for the address translation virtual-to-physical, such like in virtual addressing, but without need to flush the cache in case of page replacement, as required in virtual addressing, and without any coherency problem.
23.
A PTE may also include information about whether the page has been written to ( the " dirty bit " ), when it was last used ( the " accessed bit, " for a least recently used ( LRU ) page replacement algorithm ), what kind of processes ( user mode or supervisor mode ) may read and write it, and whether it should be cached.
