INT 10H 05H: Select Video Page

                                                          Compatibility: All 
 Expects: AH    05H
          AL    video page number (0-based)
          ──────────────────────────────────────────────────────────────────
 Returns: (none)
          ──────────────────────────────────────────────────────────────────
    Info: This selects a different video page.  CGAs,EGAs, and VGAs support
          eight video pages, but most MDAs▲ support only one.

          Historically, some text-mode programs have gotten a performance
          boost by using multiple video pages.  For instance, you can make
          a series of changes to the second video page and then use this fn
          to display the entire page all at once.

   Notes: ■ On VGAs, you may use INT 10H 1bH (get functionality/state info)
            to see how many pages the active display supports.

          ■ Most programmers select page 0 and leave it there for these
            reasons:
            • Page-switching is not possible with MDAs.
            • All newer computers are fast enough to update the screen in
              place (see Video Memory Layouts).
            • On older CGAs, writing to non-visible pages still causes
              Video Snow (so there is no performance gain).
            • Some popular mouse support driver will honor only page 0.

            However, TSRs should be aware of page-switching techniques in
            order to avoid screwing up the interrupted application.

          ■ The active video page number can be obtained via INT 10H 0fH.

          ■ The starting address of the start of the active page can be
            found in the 2-byte word at 0040:004e.  See BIOS Data Area.

See Also: INT 10H: Video Services
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