Long ago when the Mac was based on the mc68000 family of processors, and "monitors" were really big, dumb, stupid, lead-lined CRTs, Apple produced an "accelerated"
NuBus graphics card called the "8•24 GC" with a general purpose
AMD Am29000 processor in it:
The Macintosh Display Card 8•24 GC is an accelerated 12″ NuBus video card compatible with 68020– and 68030-based Macs. Acceleration is not available if the card is installed in a 68040-based Mac – in fact, the 8•24 GC control panel will bomb the computer. The card’s driver version 1.0 software...
lowendmac.com
What ran on the Am29000 was a "port" of
QuickDraw, to which all calls (from both MacOS & apps) to QuickDraw on the Mac main processor were handed off, i.e., a full-on "
graphics co-processor" which processed graphics in parallel with the CPU. In today's world, we'd call that a GPU, even though the Am29000 was general purpose processor (not specifically optimized for graphics).
Cool bit: adding an 8•24 GC card to your Mac not only accelerated graphics for its directly attached monitor, but
also for every other monitor attached to a display card on the NuBus because NuBus, you see, permitted multiple "bus masters" which meant that the Am29000 in the 8•24 GC could
directly manipulate & accelerate every graphics "frame buffer" in the system, just like the main CPU - equal access.
Pretty cool for its time. I really wish Apple had kept that software up to date, but they didn't: it died in the transition to "32-bit clean" systems because no one did the work.
What does this have to do with ARM processors in modern Apple displays?
Um, guess what they're most likely doing: offloading graphics processing that can be better (more efficiently) done "nearer" to the display (on the other side of a latency & bandwidth constrained Thunderbolt bus) than in shared main RAM of your Apple Silicon (which, yes, has GPU cores itself), so as to spread processing tasks over even more processors, for best performance & throughput. After all, Apple doesn't have to tell us where the
METAL graphics processing is done: their own proprietary drivers can split up the work as needed or desired based on available hardware (which, obviously, varies by purchased system configuration).
See also
eGPU. However, also beware the "
wheel of reincarnation" (an
important observation on the evolution of graphics processing in 1968 from the father of computer graphics,
Ivan Sutherland).