|RAM (Random Access Memory)|
|CMOS (Complementary Metal-Oxide Semiconductor)|
CPU chips are integrated circuits that contain thousands to millions of transistors. These transistors are used to process information in the form of electronic signals. The more transistors a CPU has, the faster it can process data. Several evolutions of CPUs have allowed for the chips to hold more transistors than their predecessors, and therefore process information at increasing speeds. As a technician, you will encounter several different types of processors in operation and must familiarize yourself with their various characteristics and features. The following subsections describe each chip in detail.
Prior to the 386 chip, Intel would license its technology to its competitors. But the competition found ways to make cheaper, and in some cases faster, processors. Consumers were buying these less expensive chips at an increasing rate, which cut into Intel’s market share and reduced its status as the leading manufacturer. Intel’s competitors came out with their own version of the 386 chip.
The 386 processor was also the first time that there were two versions of the same basic processor, the SX version and the DX version. The 386SX processor came with a 16-bit data bus, a 24-bit address bus, and a 32-bit register size. The 386DX processor’s data bus, address bus, and register size were all 32-bits. Both the SX and DX chips operated at 16 MHz, 20 MHz, 25 MHz, and 33 MHz.
When the 486DX was released, it had the same characteristics as the SX version, only the math co-processor was enabled. A later version of the chip, the 486DX2, was still able to run at 33 MHz externally, but doubled the processor speed, or clock speed, internally and brought it up to 66 MHz. Following that, the 486DX4 chip was released, which increased the clock speed even more and brought it up to 133 MHz.
Along with the improvements came a significant change in processor architecture and capabilities. The chip combined two 486DX chips into one, called the Dual Independent Bus Architecture, which allowed each processor inside the chip to execute instructions simultaneously and independently from each other, called parallel processing. The end result was a faster chip, but required a special motherboard that was able to withstand the enormous amount of heat generated by the chip. Heat sinks also had to be employed to help remove the excess heat from the chip or it would burn itself out.
|Processor||Physical Size||Voltage||Speed||Heat Sink||Cooling Fan||On Board Cache||Sockets||Pins|
Exam Watch: Know Table 4-2 cold for the exam, as there are several questions that will test your knowledge of the different processors’ bus size.Table 4-2 provides an overview of the different varieties of processors along with their bus sizes.
|Processor||Register||Data Bus||Address Bus|
In order to understand memory, you need to get a feel for some of the terms related to memory, such as that which describes memory sizes. Each individual 0 or 1 is called a bit, and written as a lower case "b." To try and keep track of the millions and billions of bits would prove a laborious task, so bits are grouped into sets of eight called a byte, which is written as an upper case "B". Since computers work with large numbers of bytes, it would still get a bit tedious listing files sizes of 500,000 bytes or 5,000,000 bytes. Instead, we use a form of shorthand that cuts the numbers down to a more manageable size. There are three common denotations that are used to represent computer numbers: a kilobyte (KB) is 1,024 bytes, amegabyte (MB) denotes 1,048,576 bytes, and a gigabyte (GB) means 1,073,741,824 bytes! So, if you had 16 MB of memory on your computer, you actually have 16,777,216 bytes of memory available. If you are wondering why a kilobyte, for example, isn’t equal to 1,000 bytes it is because the computer works on powers of 2 rather than 10. Thus, when we calculate 2^10, we get 1,024 bytes instead of 1,000 bytes. If we were trying to get a megabyte, we would calculate 2^20.
Memory comes in several forms, but generally the processor accesses random access memory (RAM). RAM gets its name from how the memory is physically accessed. Data can be accessed by one of two methods, either sequentially or randomly. When you store data sequentially, you cannot get immediate access to the data that you need. Instead, you must go through all of the information that had been stored before actually getting to the data that you need, which is the way that magnetic tape stores and retrieves data. However, with random access, you can bypass the data that you don’t need and go directly to the location where the information is stored. RAM allows your computer to store and retrieve data in random locations in memory.
There are several forms of RAM available, each with its own method of random access and differing physical characteristics. We discuss each in the following subsections.
Even parity works in the same manner, except that the total number of ones must add up to an even number. Therefore, if the sum of ones equals an even number, the extra bit is set to zero. However, if the sum of ones equals an odd number, the extra bit is set to one. Should one of the data bits switch, say from a one to a zero, the total number of ones will not result in the correct odd number (for odd parity) or even number (for even parity). The problem with this is that if two of the bits were switched, the data would still pass the parity test.
Parity is not just used with memory, but is utilized in hard drives and communications. While it is not a 100-percent guaranteed method of ensuring that your data is intact, it is still better than having no parity at all. With a non-parity chip, you have no guarantee that the data that is stored on the chip is what was truly sent.
SIMMs come as either 30-pin or 72-pin cards, but each card has a different format. The format is broken down as follows:
Capacity of the Chip x Data BitsThe capacity is the amount of data the card can hold, usually denoted in megabytes. However, the data bits determines if the SIMM utilizes parity. If the data bits equals 8 or 32, the SIMM does not use a parity bit, but a 9 or 36 will indicate that parity is in use (8 + 1 parity bit or 32 + 4 parity bits).
Regardless of which type of AT motherboard you are working with, the characteristics are basically the same. The processor is normally located in the front of the board, which has been an annoyance to many technicians attempting to install a new expansion card. The serial and parallel ports are actually located on the back of the case, and attach to the motherboard by headers.
There are two types of communication ports found on a motherboard: serial and parallel. Serial ports transmit data sequentially, bit by bit over a single conductor. This type of communication is usually found with modems and mice. However, a parallel port allows transmission of data over eight conductors at one time. An example of a device that utilizes a parallel port is a printer.
Industry Standard Architecture (ISA) was introduced after the IBM AT computers were released. AT computers allowed for a 16-bit data bus, but the peripherals at the time were still stuck on the 8-bit bus. To improve the communication speed of the devices, and to provide for an industry standard, several of the larger companies got together and developed ISA technology. This now allows for peripherals to utilize the 16-bit data bus that is available with 286 and 386 processors.
|Extended Industry Standard Architecture (EISA) was introduced to compete against IBM’s Micro-Channel Architecture (MCA) devices, which increased their peripheral’s bus size from a 16-bit bus to a 32-bit bus. Because MCA was expensive and proprietary, the original companies that developed ISA got together and created a 32-bit card that was not only cheaper, but retained backward compatibility with the 16-bit ISA cards. This type of bus architecture is used in conjunction with 386 and 486 processors.|
|Peripheral Component Interconnect (PCI) was designed in response to the Pentium class processor’s utilization of a 64-bit bus. Until the development of the PCI bus, peripherals were tied to the processor architecture as well as the processor data bus. However, PCI buses are designed to be processor independent. They are able to accomplish this feat by utilizing a special bridge circuit along with a processor-dependent configuration program.|
|The VESA Local Bus (VL-Bus) was originally created to address performance issues. One of the problems with earlier bus designs was that they could only handle a maximum clock speed of only 8 MHz, while processors could run at much higher clock speeds. The idea was to create a bus that would have the same clock speed as the processor, known as a local bus. Components that utilized the local bus increased their performance, and thus several types of components were designed to take advantage of the faster speed.|
|Of the kinds of components that used the new bus architecture—hard drive cards, memory cards, cache cards – video cards became the most prevalent. However, compatibility issues arose as vendors used proprietary local bus slots and cards. This meant that you had to purchase the vendor’s card in order for it to work in the vendor’s slot. The Video Electronics Standards Association (VESA) was formed to address this compatibility problem.|
|VESA created the standards for the local bus architecture that were incorporated into the manufacturer’s products. This ensured that a card from one vendor would work in another manufacturer’s computer. The VL-Bus used a 32-bit slot and was built upon ISA bus architecture. This meant that the bus was backward-compatible with ISA and that configuration would require the old jumper and/or DIP switch configuration methods.|
|The Personal Computer Memory Card International Association (PCMCIA), or the less hard to remember PC Card, bus was first created to expand the memory capabilities in small, hand-held computers. The bus itself is about the size of a credit card and is only 16-bit. While some computers utilize the PC Card bus, the 16-bit size is somewhat restricting in computers that are capable of handling 64-bits. Therefore, a new standard is currently under construction to increase the PC Card to a 32-bit standard.|
Exam Watch: Make sure that you know the differences between each type of bus and what each acronym stands for. While most of the acronyms seem intuitive, the exam will throw in a few that will seem to be just as plausible.
Over time, batteries become depleted and this resets the bios. The clock is turned back to 1904. This causes you to have to replace the battery and reset the settings. You need to choose between all the types of hard drives, or worse, fill in the blank for the cylinder numbers, heads, and so forth. Well, if you have a good hard drive, you can usually find this labeled on the drive. If not, you can always look up this information in a book if you have the manufacturer and the serial number. You will in time find some of these that have none of this information on them. I’ve seen techs reboot 79 times only to find out that the drive is not one of those preset in the CMOS. Only third-party software and much time can be the answer to this dilemma.
Get a good idea of when these batteries often die. If you find out that a certain model of computers are losing their batteries after a certain amount of time, make sure you replace the other computers that were bought at about the same time. If the clock starts losing time, you can bet that the battery is to blame. Your best defense, however, is to keep track of the BIOS settings. There are some software programs out there that will save this data and let you print it. Do so, and keep this information with the log for the computer. Not only are hard drives tough to set in the BIOS, but some BIOS have settings that are very difficult to decipher. With your list ,you will never have to guess if you should have a setting activated or not.
— By Ted Hamilton, MCP, A+ Certified
|Unidirectional A single directional mode for the parallel port. Data travels only from the computer to the printer in this mode.|
|Bi-directional A two directional mode for the parallel port. Data travels both from the computer to the printer and vice versa.|
|Disable/enable Enables or disables the parallel port.|
|ECP–Extended Capability Port ECP mode offers the same features as bi-directional in addition to the use of a DMA channel for data transfer. This speeds up data transfer rates by bypassing the processor and writing the data directly to memory.|
|EPP–Enhanced Parallel Port EPP mode offers the same features as bi-directional and offers an extended control code set.|
Exam Watch: Know the different types of parallel ports for the exam, as many people get stuck on these types of questions.
|Memory address All serial ports require a memory address. The memory address is used to receive commands from the processor that are destined for the device attached to the COM port. Each device must have a unique memory address in order for it to function.|
|Interrupt request Every COM port must have a unique interrupt. It is through this interrupt that the peripheral attached to the COM port notifies the CPU that there is data available to be retrieved from the peripheral. An example is when the modem receives data. The modem will fire an interrupt on the COM port, which in turn triggers the CPU to pick up data from the modem.|
The standard COM1 interrupt address is 4 and the memory address is 03F8. With COM2, the interrupt address is 3 and the memory address is 02F8. This has a tendency to seem counterintuitive, as COM1 would be listed before COM2.
Exam Watch: Remember the interrupt and memory addresses for both COM1 and COM2 for the A+ Certification Exam.
|Enable/disable The enable/disable either enables or disables the COM port for use.|
|Size The size of the drive is automatically calculated from the number of cylinders, sectors, and heads on the drive. If you need to calculate the size of a drive, you would use the following formula:|
(# of cylinders) * (# of sectors) * (# of heads) * 0.5 KB
|The 0.5 KB constant is due to the fact that most hard drives have 512 bytes per sector.|
|Size The size of the drive is automatically detected by the computer.|
|Primary master/secondary slave Each hard drive has a controller built into the drive itself that actually controls the drive. When you have more than one hard drive attached to an adapter card, the adapter could get confused as to which controller was in charge. In order to distinguish which controller is actually being used, one of the drives is designated as a master drive and its controller is used to control the other drives, which are called slaves. When you look at the CMOS configuration screen, you will note that you have to fill in the primary master section for the master drive, and the secondary slave section for the slave drive.|
|Tracks A hard drive is made up of several disks mounted on a spindle. Each disk can be broken down into rings of concentric circles, where each ring is called a track. The number of tracks that a hard drive has is usually printed on the outside case of the drive itself.|
|Sectors As you can break down a disk into tracks, you can further subdivide the disk into sectors. This is done by "slicing" the disk up as you would a pie. Each piece of that pie is called a sector. The number of sectors on a hard drive is usually printed on the outside case of the drive itself.|
|Cylinder When you combine the same tracks on each of the disks in a hard drive, you have what is known as a cylinder. The number of cylinders in a hard drive is also printed on the outside case of the drive itself.|
|Drive type With the older CMOS configuration utilities, you would have to manually input all of the preceding information plus the type–MFM, IDE, SCSI–drive it was. However, today’s version of the CMOS configuration utility can auto-detect the drive type and all of the preceding information. To do this, you simply set the drive to AUTO and it does the work for you. Although, you should know how to modify these settings yourself in the event that the CMOS does not recognize the drive you have.|
|Enable/disable drive When installing a floppy drive, you do have the option to disable it. To do this, you must set Drive A to None.|
|Density Drive types are usually defined by the capacity and size of the media. There are five standard types available. They are:|
|5.25" 360 KB|
|5.25" 1.2 MB|
|3.5" 720 KB|
|3.5" 1.44 MB|
|3.5" 2.88 MB|
While most people have this set up to search for a floppy drive first, you may want to set the machine to look to the hard drive first. Many customers have a tendency to leave their data disk in the drive when they turn their computers off. When they boot, the computer can’t find an operating system to load and it produces an error message. You can cut down on the number of calls by setting the boot sequence to check for the hard drive first, and the floppy drive second. However, the drawback to this is that if you do need to boot from a floppy, you will have to reconfigure this setting.
|The CPU’s job is to provide the devices attached to the computer with directives that retrieve, display, manipulate, and store information.|
|Today’s Intel Pentium II processors contain 7.5 million transistors and supports a 64-bit bus.|
|SIMM stands for Single In-Line Memory Module, which is a type of RAM chip.|
|The Intel 586 (Pentium) chip combined two 486DX chips into one, called the Dual Independent Bus Architecture. This allowed each processor inside the chip to execute instructions simultaneously and independently from each other, which is called parallel processing.|
|The PCI (Peripheral Component Interconnect) was designed in response to the Pentium class processor’s utilization of a 64-bit bus. PCI buses are designed to be processor-independent|
|Review Table 4-2, which provides an overview of the different varieties of processors along with their bus sizes.|
|As a service technician, you should familiarize yourself with each of the motherboard’s components and know what their function is.|
|There are three common denotations that are used to represent computer numbers: a kilobyte (KB) is 1,024 bytes, a megabyte (MB) denotes 1,048,576 bytes, and a gigabyte (GB)means 1,073,741,824 bytes!|
|DIMM stands for Dual In-Line Module, which is a type of RAM chip.|
|To ensure that the signals on memory chips are correct, they are constantly updated, a process called refresh.|
|WRAM, which was design specifically for the Microsoft Windows operating system, utilizes memory that resides on the card itself to perform the Windows-specific functions, and therefore speeds up the OS.|
|The number of transistors inside a chip is one of the determining factors in the rate at which a chip can process information.|
|A memory bank is the actual slot that memory goes into.|
|There are two basic types of motherboards: AT and ATX.|
|ISA (Industry Standard Architecture) is an industry standard bus architecture that allows for peripherals to utilize the 16-bit data bus that is available with 286 and 386 processors.|
|On the AT motherboard, the processor is normally located in the front of the board, which has been an annoyance to many technicians attempting to install a new expansion card.|
|The communication ports on the system board allow external devices to attach directly to the processor without having to remove the case.|
|While SRAM doesn’t need a constant update, it does require a periodic update and tends to use excessive amounts of power when it does so.|
|A serial port transmits data sequentially, bit by bit, over a single conductor and is most commonly used with modems and mice.|
|A parallel port transmits data over eight conductors at one time and is most commonly used with printers.|
|The processor socket is the actual socket used to attach the processor to the motherboard.|
|Cache memory is used to store frequently used instructions and data so that they can be accessed quickly by the computer.|
|EISA (Extended Industry Standard Architecture) is an industry standard bus architecture that allows for peripherals to utilize the 32-bit data bus that is available with 386 and 486 processors.|
|Originally created to address performance issues, the VL-Bus was meant to enable earlier bus designs to handle a maximum clock speed equivalent to that of processors.|
|The Personal Computer Memory Card International Association (PCMCIA), or the less hard to remember PC Card, bus was first created to expand the memory capabilities in small, hand-held computers.|
|Make sure that you know the differences between each type of bus and what each acronym stands for. While most of the acronyms seem intuitive, the exam will throw in a few that will seem to be just as plausible.|
|Know the different types of parallel ports for the exam, as many people get stuck on these types of questions.|
|The memory address is used to receive commands from the processor that are destined for the device attached to the COM port. Each device must have a unique memory address in order for it to function.|
|The standard COM1 interrupt address is 4 and the memory address is 03F8.|
|With COM2, the interrupt address is 3 and the memory address is 02F8.|
|Each hard drive has a controller built into the drive itself that actually controls the drive.|
|The number of tracks, sectors, and cylinders on a hard drive is usually printed on the outside case of the drive itself.|
|Integrated NICs are not a common component found in computers.|