CMOS Battery

Your PC has to keep certain settings when it’s turned off and its power cord is unplugged.
These settings include the following:

1. Date
2. Time
3. Hard drive configuration
4. Memory

Your PC keeps these settings in a special memory chip called the Complimentary Metal Oxide Semiconductor (CMOS) chip.

Actually, CMOS (usually pronounced see-moss) is a type of memory chip; it is the parameter memory for the BIOS. But that doesn’t translate into an easy-to-say acronym.

So because it’s the most important CMOS chip in the computer, it has come to be called the CMOS.

To keep its settings, the memory must have power constantly. When you shut off a computer,
anything that is left in main memory is lost forever.

To prevent CMOS from losing its information (and it’s rather important that it doesn’t), motherboard manufacturers include a small battery called the CMOS battery to power the CMOS memory.

The batteries come in different shapes and sizes, but they all perform the same function. Most CMOS batteries look like either large watch batteries or small, cylindrical batteries.

BIOS Chip

Aside from the processor, the most important chip on the motherboard is the Basic Input/Output System (BIOS) chip.

This special memory chip contains the BIOS software that tells the processor how to interact with the rest of the hardware in the computer.

The BIOS chip is easily identified: If you have a non-clone computer (Compaq, IBM, HP, and so on), this chip has on it the name of the manufacturer and usually the word BIOS.

For example, the BIOS chip for a Compaq has something like Compaq BIOS printed on it. For clones, the chip usually has a sticker or printing on it from one of the major BIOS manufacturers (AMI, Phoenix/Award, Winbond, and so on).

Motherboard Attachment

There are two ways of connecting these ports to the motherboard (assuming the circuitry for
providing these functions is integrated into the motherboard).

The first, called a header connection, allows you to mount the ports into the computer’s case, usually on the backplane, with a special cable connected to a header, or male connector that terminates the motherboard’s traces for that function.

The second method of connecting a peripheral port is known as the direct-solder method.

With this method, the individual ports are soldered directly to the motherboard.

This method is used mostly in integrated motherboards in non-clone machines.

Notice that there is no cable between the port and the motherboard and that the port is part of the motherboard.

As discussed earlier, these onboard ports can be disabled in the BIOS setup if necessary.















Connecting a port to the header on a motherboard












Peripheral ports directly soldered to a motherboard

Peripheral Ports and Connectors

In order for a computer to be useful and have the most functionality, there must be a way to get the data into and out of it.

Many different ports are available for this purpose.

Briefly, the seven most common types of ports you will see on a computer are serial, parallel,
Universal Serial Bus (USB), video, Ethernet, sound in/out, and game ports.

1. DC power in
2. Analog modem RJ-11
3. Ethernet NIC RJ-45
4. S-video out
5. DVI-D out
6. SVGA out
7. Parallel (on top)
8. Standard serial
9. Mouse (on top)
10. Keyboard
11. S/PDIF (out)
12. USB

Peripheral Ports and Connectors




Game Port

Keyboard Connectors

The most important input device for a PC is the keyboard. All PC motherboards contain a connector that allows a keyboard to be connected directly to the motherboard through the case.

There are two main types of keyboard connectors. Once, these were the AT and PS/2 connectors. Today, the PS/2-style connector remains popular, but it is quickly being replaced by USB-attached keyboards.

The all-but-extinct original AT connector is round, about 1⁄2 inch in diameter, in a 5-pin DIN configuration.

The PS/2 connectoris a smaller 6-pin mini-DIN connector.

Most new PCs you can purchase today contain a PS/2 keyboard connector as well as a PS/2 mouse connector right above it on the motherboard.

AT keyboard connector










PS2 keyboard connector

Onboard Floppy and Hard Disk Connectors

Almost every computer made today uses some type of disk drive to store data and programs until they are needed.

Most drives need a connection to the motherboard so the computer can “talk” to the disk drive.

These connections are known as drive interfaces, and there are two main types: floppy drive interfaces and hard disk interfaces.

Floppy disk interfaces allow floppy disk drives (FDDs) to be connected to the motherboard and, similarly, hard disk interfaces do the same for hard disks.

When you see them on the motherboard, these interfaces are said to be onboard, as opposed to being on an expansion card (off-board). The interfaces consist of circuitry and a port.

Most motherboards produced today include both the floppy disk and hard disk interfaces on the motherboard.

Today, the headers you will find on most motherboards are for Enhanced IDE (EIDE/PATA) or Serial ATA (SATA).

Advanced Technology Attachment (ATA) is the standard term for what is more commonly referred to as Integrated Drive Electronics (IDE).

The AT component of the name was borrowed from the IBM PC/AT, which was the standard of the day.

However, because ATA is not the only technology that integrates the drive controller circuitry into the drive assembly (ESDI, for example, was another), IDE is somewhat of a misnomer and not the best term when referring only to ATA drives.

Nevertheless, the original ATA standard was referred to as IDE and had an upper limit of
528MB per logical drive.

An enhanced version, Enhanced IDE (EIDE), was developed to circumvent the obstacles to accessing more drive space per volume, increasing the limit to 8GB.

Since then, the limit has been increased to 144PB through various enhancements. A petabyte
(PB) is the number of bytes represented by 2 raised to the 50th power.

If your motherboard has PATA headers, they will normally be black or some other neutral color if they follow the classic ATA 40-wire standard.

If your PATA headers are blue, these represent PATA interfaces that employ the Ultra DMA (UDMA) technology that increases transfer rates by reducing crosstalk in the parallel signal by alternating another 40 wires that act as grounds among the other wires.

The connectors and headers are still 40 pins, however.

The color coding alerts you to the enhanced performance, which is downward compatible with the 40-wire technology.

The original 40-pin ATA header transfers data between the drive and motherboard multiple bits in parallel, hence the name Parallel ATA (PATA).

SATA, in comparison, which came out later and prompted the retroactive PATA moniker, transfers data in serial, allowing a higher data throughput because there is no need for more advanced parallel synchronization of data signals.

The SATA headers are vastly different from the PATA headers.

Many motherboards, especially higher-end boards like those found in servers, also include the more complex SCSI circuitry built in so that SCSI-attached drives can connect directly to the system board without an external adapter.

a SATA connector

Power Connectors

In addition to these sockets and slots on the motherboard, a special connector allows the motherboard to be connected to the power supply to receive power.

This connector is where the ATX power connector (mentioned later in this chapter in the
section “Identifying Purposes and Characteristics of Power Supplies”) plugs in.















An ATX power connector on a motherboard