After several false starts, the MacBook now has four times the memory it had yesterday:
- My set of six electronics screwdrivers didn't include a cross-head small enough to open the casing; the smallest flat-head worked. Just.
- After first attempt, it wouldn't boot.
- Put original memory back. Booted, with lots of screen/cursor corruption; turns out one of the slots wasn't detecting the card.
- Put new memory back again, and this time it all worked. Phew.