How To Build A PC

Step 13: Install Cables, Cards And Drives

Since legacy PCI has mostly gone extinct, modern expansion cards are usually available as PCI Express (PCIe). Available in single-, four-, eight-, and sixteen-lane versions, the PCIe standard retains compatibility between shorter cards and longer slots. The below image shows a PCIe x1, PCIe x16, and PCI slot for comparison.

PCIe allows shorter cards to be placed in longer slots, such as an x1 card in an x16 slot. Conversely, longer cards can only be placed into shorter slots when the forward end of that slot has no cap. Since the difference between open-ended and closed slots isn’t easily seen in photos or explained on motherboard specification sheets, many manufacturers use x16 slot connectors for their four and eight-lane interfaces.

Although our example motherboard includes on-board graphics, we chose to use a PCI Express graphics card for enhanced performance. The PCIe x16 card is inserted until a latch on the slot engages the card's hook. These latches are present on most PCI Express x16 slots, but are not found on lower-bandwidth PCI and PCI Express x1 interfaces. Finally, a case screw or quick-release latch secures the top of the card's metal bracket at the opposite end.

Internal 3.5" drives are traditionally secured with coarse threaded case screws, while external drives, 2.5" drives and bay devices usually have fine metric threads. External drives typically slide in from the front, while internal drives often slide in from inside the case.

Several manufacturers offer tool-free installation using drive rails, sliding latches, or other pin-loaded devices that engage with screw holes. Our case reviews highlight several designs.

The motherboard cables of new systems are usually based on the expanded EPS12V standard, which encompasses previous ATX standards. Previously found on server-sized EPS power supplies, the 24-pin main power cable is both forwards and backwards compatible with the earlier 20-pin part. The below example shows how a 20-pin plug fits into a 24-pin socket; the wide latch is designed to work with either 20-pin or 24-pin plugs.

One of the reasons for a 24-pin power cable includes added amperage supplied to PCI Express slots compared to older interface standards. While most cards won't overdraw a 20-pin connector, graphics card makers occasionally have suggestions for a higher minimum level of available power.

The 4-pin or 8-pin ATX 12V connector satisfies the electrical demands of the CPU. Formerly known as the "P4" power connector, it was added by Intel to supplement its Pentium 4 processors, and later adapted by AMD motherboard designers. The newer 8-pin versions were originally meant to address phenomenally power-hungry Pentium D and Prescott-based Pentium 4s, but many modern AMD and Intel processors are efficient enough to once again work from 4 pins. Most 8-pin boards will work with both 8-pin and 4-pin power, as the connectors are cross compatible.

Also seen in the photo above is a 4-pin CPU fan power connector and the front-panel audio connector. On-board 4-pin fan connectors are designed to provide pulse width modulation (PWM) automatic speed control, but the connectors are once again cross compatible with 3-pin fans. Some motherboards are able to control fan speed via either voltage changes or pulse width, while others will run the “wrong” fan at full speed, continuously, without harming the system.

Front panel audio cables are often available with both AC97 and HD-Audio connectors, where HD-Audio is a slightly newer standard and AC97 is extinct. Using the "wrong" connector may temporarily reduce the number of available audio channels, but will not harm any components. The key-pin for audio headers is in a different location from other panel connectors to ease installation.

The case's power switch, power indicator light, reset switch, and hard drive activity light are usually connected at the motherboard's lower-front corner. LEDs pass current in only one direction, and positive pins (indicated by a "plus" sign below) normally connect to the colored wire on each lead. A black or white lead wire usually indicates negative or ground state. If your power and reset switches work but your power and HDD lights don't, your LED connectors are probably flipped.

USB connectors have been standardized for over fifteen years, and we suggest that first-time builders not attempt to incorporate any parts older than that. The missing pin location is blocked by most front-panel USB connectors to assure that the connector is polarized correctly. A reversed connection would damage the motherboard, so 4-pin, 8-pin, or single-row internal break-out cables require special care. The missing pin indicates the negative/ground end of the connector.

Device Cable Installation

Serial ATA (SATA) power and data cables are keyed on the sides, as seen on the drive below. Some early SATA drives were also able to accept older 4-pin ATA power connectors. The sticker warns that builders should choose either SATA or legacy power, but not both.

Many PCI Express graphics cards require more power than the slot is able to provide, and use the 6-pin input connector shown below or a newer, higher-amperage 8-pin version. The 6-pin connector must never be confused with 4-pin or 8-pin motherboard power, as its polarity is the opposite of those. Fortunately, the newer 8-pin PCI Express power cables are designed in such a way that they cannot be forced unintentionally into a motherboard’s 8-pin connector.

Are you trying to rescue data from an outdated drive on your new system? New motherboards don’t support these drives natively, old SATA-to-ATA converters often had limited compatibility, and old drive interface cards used legacy PCI. If you really are stuck trying to pull childhood photos off a deceased family PC, we’d like to suggest installing the drive in an external USB-based adapter.

ATAPI and Ultra ATA drives have pin 1 on the "other" side of the connector, as seen when facing it (on the right in the photo below). A key is located on the top of all 80-conductor ATA cables to prevent upside-down insertion.


No system is complete without software, and most operating systems are available on a bootable DVD. The system's boot order can be selected in the motherboard BIOS, usually under the "Advanced BIOS Features" menu, and should be set to boot from CD first. Many modern motherboards will list the actual name of the drive in the boot order, while others will only list it by device type.

Further BIOS tips and tricks can be found in our BIOS for Beginners.

We hope that this series has made your build a complete success, but if it hasn't, members of our Community Forums eagerly anticipate your technical questions.

MORE: Best PC Builds
MORE: Systems in the Forums

Thomas Soderstrom is a Senior Staff Editor at Tom's Hardware, covering CasesCoolingMemory and Motherboards. Follow him onTwitter.

Chris Miconi is an Associate Contributing Writer for Tom's Hardware, covering Cases

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  • James_39
    Selecting the case is a bizarre thing to have in Step 1.Surely that would be best placed once all other components, including accessories, have been factored in? Otherwise you end up selecting components purely on the basis they fit in your case, not forgetting that some (most) cases don't support water cooling kits/pipes etc mentioned in Step 8.