Since both use the same DDR RAM, yes, it's safe to use the RAM from the other laptop in the faulty 9100. RAM falls into standard families, nowadays DDR3, previously DDR2 and in the case of these older laptops, DDR1.
Since both use the same DDR RAM, yes, it's safe to use the RAM from the other laptop in the faulty 9100. RAM falls into standard families, nowadays DDR3, previously DDR2 and in the case of these older laptops, DDR1.