型号是什么?

DDR should not have anything like "2533". If it is DDR2-533, you can't put them together.

If both are DDR 400 (consider P4), you might be able to. I might still have some DDR 400 left and let me know if you need them.

I am a gadget sink and hate to see things go wasted. :)

DDR-400 is the highest it goes.

Standard name	Memory clock (MHz)	Cycle time[4] (ns)	I/O bus clock (MHz)	Data rate (MT/s)	VDDQ (V)	Module name	Peak transfer rate (MB/s)	Timings (CL-tRCD-tRP)
DDR-200	100	10	100	200	2.5±0.2	PC-1600	1600
DDR-266	133⅓	7.5	133⅓	266⅔		PC-2100	2133⅓	2.5-3-3
DDR-333	166⅔	6	166⅔	333⅓		PC-2700	2666⅔
DDR-400A DDR-400B DDR-400C	200	5	200	400	2.6±0.1	PC-3200	3200	2.5-3-3 3-3-3 3-4-4