Jumpers
Jumpers are very basic circuit bridges used to configure a computer's internal settings. A jumper is a small metal conductor covered in plastic (see picture below).
Jumpers complete simple connections between a single pair of pins or within a larger matrix of pins. Jumpers may also be used in more demanding situations, to connect multiple pairs of pins in complex arrangements. When a number of "jumps" need to be made, dual in-line package (DIP) switches are a practical alternative to jumpers.
DIP switches are extremely small switches that complete pinned connections. A DIP switchs "on" and "off" position pattern represents different settings. DIP switches can be configured as either a rocker or sliding type switch.
The motherboard manual will list different jumper settings, based on values for the CPUs core voltage, bus speed, and clock multiplier. Match the values with those listed in the manual to determine which jumpers belong on which pins.
Motherboards have both two- and three-pin configurations. If it is necessary to jumper a three-pin configuration, refer to the motherboard's schematic to determine which pin is labeled "1." The plastic jumper will need to be placed over either pins "1" and "2" (1-2) or over pins "2" and "3" (2-3).
When using 2-pin jumpers, the status will be either "on" or "off," meaning the jumper is either on the pins (the circuit is closed) or off the pins (the circuit is open).
With 3-pin jumpers, 1-2 means that the first and second pins are covered to close the circuit, while 2-3 means that the second and third pins are covered to close the circuit.
Configuring the Motherboard: Setting Motherboard JumpersBefore anchoring a new motherboard to the chassis, make sure it is jumpered (or strapped) according to the CPU's requirements and manufacturer's specifications. The required settings for CPU jumpering are: core voltage, CPU bus speed and clock multiplier.
To jumper a motherboard, you must know the CPU's processor speed, CPU core voltage, and CPU bus speed. These values are all provided in the manufacturer's documentation.
CPU Core Voltage, CPU Bus Speed, and CPU Processing Speed
Determine the following three CPU requirements before jumpering the motherboard:
- CPU core voltage is the voltage necessary to run the CPU.
- CPU bus speed indicates how fast the processor communicates with the chip set.
- CPU processing speed is how quickly the CPU processes information.
Newer motherboard manuals include CPU model information to expedite jumpering. Other motherboard manuals provide a range of settings for several CPU models.
Begin jumpering the motherboard with the very important core-voltage setting. An improper core voltage setting can damage the processor, motherboard, and other sensitive circuitry. After setting the core voltage, set the CPU bus speed and CPU clock multiplier. A table, like the one shown below, will be available in the motherboard manual.
| CPU Clock Speed | |||
|---|---|---|---|
- CPU Core Voltage Settings
- on =jumper is on the pins and the circuit is closed.
- off =jumper is off the pins and the circuit is open.
Mismatching a CPUs voltage setting can result in a damaged processor, motherboard, or both. Even if the result of an incorrect voltage setting is not as dramatic as "fried equipment," a computer will not operate properly with incorrect voltage settings.
Voltage setting information is available in the motherboards manual. Set jumpers according to the manuals specifications.
Example CPU Core Voltage settings:
The table above provides sample CPU voltage settings for a motherboard with 2-pin jumpers. Other motherboards may have 3-pin jumpers.
| CPU Voltage | 3P9 | 3P10 | 3P11 | 3P12 | 3P13 |
|---|---|---|---|---|---|
- CPU Bus Speed Settings
Bus speed setting information is available in the motherboards manual. Set jumpers according to the manuals specifications.
Example CPU Bus Speed settings:
The table below provides sample CPU bus speed settings for a motherboard with 3-pin jumpers. Other motherboards may have 2-pin jumpers.
| Bus speed (MHz) | 3P1 | 3P2 | 3P3 |
|---|---|---|---|
- CPU Clock Multiplier
Clock multiplier information is available in the motherboards manual. Set jumpers according to the manuals specifications.
To determine the clock multiplier value, divide the processor speed by the bus speed. For example, if a 500MHz processor runs on a 100MHz bus, the clock multiplier is 5.
CPU Clock Multiplier settings:
The table below provides sample CPU multiplier settings for a motherboard with 2-pin jumpers. Other motherboards may have 3-pin jumpers.
| Multiplier | 3P4 | 3P5 | 3P6 |
|---|---|---|---|
How would you configure the jumpers on the motherboard shown below according to the following specifications: 450MHz processor, 100MHz bus, and 1.5V core voltage?
Most modern motherboards automatically configure the core voltage, bus speed, and clock multiplier for new CPUs.
How can you preserve your investment? Make sure to buy a server that is designed for the future. Even if the server does not initially have the latest processor, the largest hard drives, or the most gigabytes of RAM, make sure that a sufficient number of slots and interfaces are available for more to be added later. It is usually cheaper to do an upgrade than an entire system swap, especially considering the cost of labor.
Conclusion
CPUs are amazing pieces of hardware. Modern CPUs have tens of millions of transistors that change states hundreds of millions of times per second. Nonetheless, to cope with today’s overwhelming network activity, servers often require two or more CPUs.
When selecting a new CPU, one must consider many features, such as frequency, cache size, and the number of times that data is transferred per clock cycle. In addition, one must verify that the CPU is compatible with a servers motherboard, operating system, and BIOS. When installing multiple CPUs, each must be of the same stepping.
Though proper CPU installation can be complex and time consuming, it is one of the most important upgrades performed by server administrators.
