The first digit tells the form factor: 6000 is the thin "pizzabox" form as in the Quadra 610; 7000, the taller "deepdish pizza" form as in the Quadra 650 (but the number derives from the Quadra 700); and 8000, the minitower form as in the 840.
Other designations will be: 9000, for a larger tower form as in the Quadra 950; 5000, for allinone machines; 3000 and 4000, for smaller, LC form factors; 1000, for PowerBooks; and 2000, for PowerBook Duos. The second digit indicates the PowerPC chip inside: 100, for the 601; 300, for the 603; and 400, for the 604. For the 620 chip, 500 may be used. The third and fourth digits will be reserved for later models.
