Original sentence: A number of common resolutions have been used with computers descended from the original IBM PC.Apple Macintosh.Associated with the screen resolution and refresh rate is a display adapter.Earlier display adapters were simple frame-buffers, but later display standards also specified a more extensive set of display functions and software controlled interface.However, whereas VGA had 256k of video memory, MCGA only had 64k, which limited it to black and white at 640x480 and 256 colors in  320x200 mode.IBM PC.Introduced on selected PS/2models in 1987, with reduced cost compared to VGA, MCGA had a 256 color (from a 262,144 color palette) mode, and a 640x480 monochrome resolution mode.Professional Graphics Adapter (PGA), introduced in 1984 for the 8-bit PC-bus, intended for CAD applications,a triple-board display adapter with built-in processor, up to 640× 480 at 256 colors and 60 Hz frame rate.Some of these are now supported by other families of personal computers.These are de-facto standards,usually originated by one manufacturer and reverse-engineered by others, though the VESA group has co-ordinated the efforts of several leading video display adapter manufacturers.Video standards associated with IBM-PC-descended personal computers include:
Edited sentence: However, whereas VGA had 256k of video memory, MCGA only had 64k, and was limited to black and white at 640x480 and limited to 320x200 for 256 color operation.Precursor to VGA, MCGA introduced a 256 color (from a 262,144 color palette) mode, and a 640x480 resolution mode