[comp.graphics] Shadowing Video RAM

mmm@cup.portal.com (Mark Robert Thorson) (06/29/89)

The new Intel chip, the 82335, has the ability to shadow video RAM.
As with the BIOS ROM, this shadowing can be set to read-only.  Could
someone please tell me what this is used for?  The Intel documentation
(Microprocessors and Peripherals Handbook, 1989) says it can be used
to speed up access to frame buffers.  If the frame buffer is on the 
expansion bus, access to it may be much slower than access to an image of
it in on-board memory.  But the image must be written back to video RAM.
What good does it do to shadow video RAM?