The IntelliStation R Pro Series by IBM covers two model types of computers: the 8654 and the 6851. The main difference between the two models is the CPU type. The 8654 has a 1.0 GHz Intel Pentium III and the 6851 has a 1.13 or a 1.26 GHz Intel Pentium III. Both computers share the same memory specs. They have a maximum memory of 4GB and a pre-installed removable memory of 256MB. To increase the RAM system memory, install a maximum of 1GB of RAM in each of the four open sockets. Only RAM with a PC133 Registered ECC SDRAM DIMMs will be compatible.