T908 Ink

Both fit the same machines. T908 is the higher-capacity option, holding more ink than the standard T907. On a busy shared printer the larger cartridge is normally the better choice, simply because it means fewer interruptions as well as a lower cost per page.

Yes. There is no problem running a standard cartridge in one slot and a higher-capacity one in another, which is useful when black runs down faster than the colours — and on an office machine it invariably does.

No. Each colour is separate, so you replace only what has emptied. Given the size of these cartridges, buying the full set at once is rarely necessary unless several are low together.

Remove it and wipe the copper chip with a dry lint-free cloth, then refit firmly until it clicks. A poor contact on the chip is the usual cause. If it persists, switch the printer off at the mains for a minute before trying again.