MacOS – Why does the macbook pro displays random garbled blocks

It was bad memory. I had upgraded to 8GB, but at some point suspected the memory for some other problem, so put the original Apple 4GB back in. Both problems went away (tested for 3 months) so I ditched the 8GB and got 16GB of higher quality memory that more closely matched the timing specifications of the original Apple memory.

So far, after two months, I haven't seen this or the other issue yet. So in this case it was bad (or wrong) memory.

The tech specs for your model are on Apple's support site.

If you have a display that has a native Displayport input (many mid-range and up displays from the past 2-3 years), you can output up to 2560x1600. Typically these displays have a full-size Displayport connector, so you'll need an adapter or cable that goes from Mini Displayport to standard Displayport - they can be found pretty cheaply at Monoprice or Amazon.

You can also output up to 2560x1600 using a Mini Displayport to Dual-link DVI adapter, however these have been problematic in the past and run around $100+. Not a great option unless you already have a monitor with a resolution higher than 1920x1200 and it doesn't have a Displayport input.

Using adapters for single-link DVI, HDMI or VGA, you can support up to 1920x1200.