Acorn BBC Micro Model B+

Acorn's stopgap between the Model B and the Master: 64K or 128K of memory with shadow RAM for the screen, freeing space that the B could not spare, and the 1770 floppy controller as standard. Sold mainly into schools already committed to the platform, and unloved at the time for being neither one thing nor the other. That makes it uncommon now, and it runs a body of later software that will not fit a Model B.