Form Factor

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Server Racks

Servers, routers and many other back-office IT devices are designed to mount in steel racks that are 19 in. wide. In this case, form factor describes the height of a component in multiples of U (or 1.75 in.). Thus we might have a 1U server, a 2U patch panel or a 6U housing for server blades. The standard rack is 42U high.

Portable Computers

For notebooks, we talk about desktop replacement (meaning big, heavy and relatively cheap), multimedia (bigger, heavier, not cheap), thin and light (topping out at about 1 in. thick and no more than 4 to 5 lbs.), and ultrathin or ultralight (under 4 lbs., sometimes under 3). Then there's the Tablet PC, Microsoft Corp.'s spec for ink-enabled touch-screen computers that includes two form factors: the simpler slate (no attached keyboard, and designed to be attached to a docking station) and the heavier but more versatile convertible, with an integrated keyboard.

For handheld PCs (HPC being another Microsoft spec) and PDAs, no clear set of form factors has emerged, although some smart phones with PDA capability (such as PalmOne Inc.'s Treo 600) are now described as having a small PDA form factor.


For microprocessors, form factor generally refers to the physical interface between the CPU and the motherboard. We speak of generic form factors or technologies, such as FC-PGA (flip chip pin grid array), where chips are turned upside down and attached using a matrix of solder balls instead of wires. The layout or contact mechanism might be further characterized as PPGA (plastic pin grid array), TCP (tape carrier package) or CPGA (ceramic pin grid array).

Another type of CPU form factor is the name of the attachment mechanism, such as Socket 478 (the numeral refers to the number of contact points), Slot 1 or Slot A.

Memory Chips

For dynamic RAM chips, the most common form factor is the 168-pin dual inline memory module, or DIMM, where RAM chips are located on both sides of a small circuit board that plugs into a designated socket on the motherboard. These are too large for many notebook computers, however, which use a smaller type of module called SODIMM, or Small Outline DIMM, with either 72 or 144 pins.

Kay is a Computerworld contributing writer in Worcester, Mass. You can contact him at

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PC Cases

1. File server (20.6 in. high, 10 drive bays) 2. Super midtower (20.3 in. high, 10 drive bays) 3. Super minitower (16.75 in. high, nine drive bays) 4. Minitower (16.6 in. high, eight drive bays) 5. Desktop (5.25 in. high., seven drive bays) 6. Ultraslim minitower (or mini desktop: 12.75 in. high or 3.6 in. high, three drive bays) 7. MicroATX cube (7.9 in. high, four drive bays).

PC Cases

Antec Inc., Fremont, Calif.


Copyright © 2004 IDG Communications, Inc.

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