PC Hardware

CPU Upgrades

Installing a new CPU is becoming less common as the prices of new motherboard/ CPU combinations (and even new machines) continue to drop. In many cases, installing additional memory is a more effective upgrade than installing a new CPU. Still, as a technician, you need to know how to update the CPU in an existing machine.

In many cases, upgrading a CPU is as simple as removing the old one and inserting the new one. First, you need to determine whether the CPU can be upgraded and, if so, to what? The answer to this question lies in the motherboard. The motherboard must have the appropriate socket, data bus, address bus, and crystal to support the new CPU. Consult the documentation that comes with the motherboard-this documentation usually contains a table that defines which CPUs can be installed. If you are unable to find the documentation, or the processor that you want to install is not listed (because it's of newer vintage than the documentation), you will need to consult the motherboard manufacturer either through the company's Web site or with a phone call to the company's tech support department. Be sure to check on any required jumper settings and BIOS upgrades at the same time.

A small upgrade, going from one level of the same CPU family to another, is usually no problem. But if you want to upgrade a 386 to a Pentium, or a Pentium to a Pentium III, a new motherboard is the only answer. The same is true if the CPUs are coming from different chip makers. Refer to Tutorial 4, Lesson 2: Replacing and Upgrading Chips, for possible scenarios.

General Procedure for Installing a CPU

Perhaps the most difficult part of upgrading a CPU is determining the limits imposed by the motherboard. But after the decision is made and you have the new processor in hand, the actual installation is quite easy. Follow this general procedure to install a CPU:

  1. Turn off the computer and unplug the power cord.
  2. Disconnect external devices (AC power and monitor power).
  3. Follow the appropriate ESD safety procedures.
  4. Remove the cover of the computer.
  5. Locate the socket for the CPU. It might be on the motherboard or on a removable processor card.
  6. Remove the old processor. This may require special tools for older processors. Pentium II and III packages are Slot 1 designs, which slide into a slot much like those used for an expansion card. The original Pentiums (60-166 MHz) and Pentium Pro models usually have a ZIF (zero-insertion-force) socket. The ZIF socket is opened by moving the handle to the upright position. (This should not require force.) The CPU can then be easily removed.
  7. Install the new processor. Be certain to align the chip properly (this is critical!). Pin 1 on the CPU must fit pin 1 in the socket. There are several ways to identify this pin. Various chip manufacturers, and different versions of a manufacturer's chips, use different methods to mark installation orientation. Slot 1 CPU packages, for example, have a key in the slot, and it fits only one way. Other CPUs have similar schemes appropriate to their socket design. Look for a key pinhole in one corner, a blunt edge on one corner of the socket, a dot, a corner with a pin arrangement that differs from the others, or some other identifying mark. Align this mark with the corner of the socket that contains a blunt edge. If you encounter any resistance or you have to apply any pressure when inserting the CPU, recheck the chip's orientation and alignment, and reinsert the chip. After the chip is in place, secure the ZIF handle. You might need to check the documentation to make sure the chip is installed correctly.
  8. Set any jumpers or switches on the motherboard. Check the documentation.
  9. Replace the cover and power up the computer.
  10. Reconnect any peripherals (keyboard, mouse, monitor).
  11. Make changes to the CMOS setup, if required.

Some CPU upgrades also require the installation of a new voltage regulator and/or cooling fan. Be sure to check the motherboard and CPU documentation for this possibility. Failure to install these parts with the new CPU might destroy the CPU.

If you are working with a motherboard that has the ability to hold more than one CPU, both CPUs must be of the same type and from the same manufacturer if more than one is actually installed. In addition, on Pentium II and later systems, most such motherboards have a special card that must be inserted in any empty CPU slot, and the appropriate slot must be used for a single CPU configuration.