✦ Many nationwide vendors offer you the choice of doing repairs your- self according to their instructions (with component exchange by mail), opting for mail-in repairs, or having onsite repairs performed. Local stores generally offer a choice of walk-in or onsite repair. ✦ Third-party repair companies flourished and then died out in the mid-eighties. The industry trend of outsourcing support operations has once again created third-party companies that, if your business or need is big enough for them to care, will contract with you for service and support operations. ✦ Many people have friends with good computer experience. If your friends are sufficiently experienced, and are willing, they may be able to do upgrades and repairs for you. What you support yourself and what you support with outside help isn’t an all- or-nothing decision. Many companies do in-house computer upgrades, leaving repairs to others. Choosing your approach for maintenance and support need not be a complex process — figure out what your choices are, weigh those choices by your past experience and any current information you can get, and pick. Don’t forget to account for the value of faster service (whether it’s in- house or outside). Summary ✦ No matter what computer you buy, there’s a faster one coming soon. ✦ The fastest computer might not be the one you need — you need the one that does your work well at a price that fits what you want to invest. ✦ The minimum requirements Microsoft states for Windows are unreal- istically low. ✦ Virtually any computer still running meets the minimum require- ments for Windows and UNIX, but you may need more speed for spe- cific applications. ✦ You’ll end up wanting at least 20GB or more of hard disk space, and probably much more. 26 Part I ✦ Introduction 3 3 CHAPTER PC Overview Y our computer looks like a box accompanied by a screen, keyboard, and mouse, but there’s a lot hidden inside that box. You choose many components located in the box when you buy a new computer, but too many people do so based on specifications without understanding what those components are and what the specifications mean. This chapter is a tour of your PC with the covers off, identifying the components inside, what they do, and what their important charac- teristics are. What’s Inside Your Computer? Figure 3-1 shows the inside of a typical computer, and identifies each of the core components: processor, mem- ory, bus, input/output (I/O), disk, display, and power supply. The minimum set of components you need to run instructions is a processor supported by memory and a power supply. A power supply is necessary to make the electronics work at all; the memory holds instructions and data while the processor works execut- ing instructions. The chassis holds all the components together, protects them from damage, and provides shielding to prevent interference with radios, televi- sions, and other electronic devices. ✦✦✦✦ In This Chapter Examining processors, memory, and buses Understanding disk drives and input/output (I/O) channels Exploring video cards and monitors Fitting components into the whole ✦✦✦✦ Figure 3-1: Components inside a computer ©2004 Barry Press & Marcia Press A computer with nothing but a processor, memory, and power supply isn’t very useful because it can’t communicate with you or with other computers. Each of the other core components exist to either store information or let the processor communicate: ✦ Bus — Connects the processor to the memory, I/O channels, and display ✦ I/O channels — Connects the bus (and therefore the processor) to the disk, keyboard, mouse, network, and any other devices ✦ Disk — Stores large amounts of information, retaining that informa- tion even when the power is off ✦ Display — Draws images and characters on a monitor, giving pro- grams a way to output in a way you can read I/O Processor (under fan) Memory DVD writer Power supply PCI and AGP bus Video card Disk drives 28 Part I ✦ Introduction These components connect together through the bus as shown in Figure 3-2. The bus stars out from the processor to everything else because all the infor- mation flows between the processor and the other components. The operation of the components in your computer is very repetitive: the processor grabs an instruction from memory, and decides what the instruction says to do. Based on what the instruction requires, the processor grabs more information from memory or disk, operates on it if ordered to by the instruction, and then stores the data back in memory, on disk, or in the display card. The processor does this basic cycle billions of times every second it’s turned on. Little besides turning the computer off stops the repetitive sequence. Figure 3-2: A computer consists of a processor plus components to store and communicate information. A special signal inside the computer, called the clock signal (or just the clock), synchronizes components in the computer, providing the cadence to which the entire assembly marches. The clock times every action by the processor and sets the synchronization requirements for all the other components. Every instruction executed by the processor starts on the beginning of a clock cycle and lasts for one or more clock cycles. Processor Bus Memory Disk Display card Monitor Chapter 3 ✦ PC Overview 29 Processors and instructions Figure 3-3 shows what a processor looks like, while Figure 3-4 shows what the chip inside the package looks like. Figure 3-3: An Intel Pentium 4 processor packaged for use Photo courtesy Intel Corporation When programs run, their instructions are stored in memory. An instruction execution cycle starts when the processor reads the next instruction from memory. The memory receives the read command over the bus and then one or more clock cycles later returns the requested instruction back across the bus to the processor. The processor decodes the instruction and decides what has to be done to carry it out. If the instruction requires an operand from memory, the processor calculates the address of the operand and commands the memory to fetch the operand. The processor completes gathering the nec- essary data after some number of clock cycles, computes the result, and if nec- essary stores it back to memory, disk, or the display. The length of each instruction execution cycle determines the performance of the computer. If a computer running at a clock speed of 4 GHz can complete an instruction every clock cycle (including reading the instruction and data, com- puting the result, and storing back to memory), it will execute 4 billion instruc- tions per second. If the average instruction takes two clock cycles, it will execute 2 billion instructions per second, and no more. Each instruction oper- ates on one or more pieces of information, the operands of the instruction. An instruction might add or compare two numbers or might search a set of num- bers for a specific value. Executing instructions is the work the processor does. The tasks the processor carries out — tracking actions you take with the keyboard, joystick, or mouse; rendering and presenting the graphics on the display; moving information from disk to memory and back; communicating with your network; running your desktop accessories; or keeping the current print job going — each require some number of instructions to complete. The number of instructions required divided by the number of instructions per second determines how long each task takes. 30 Part I ✦ Introduction Figure 3-4: The chip inside an Intel Pentium 4 processor Photo courtesy Intel Corporation The actual number of instructions the processor executes per second is deter- mined by a lot of factors, including: ✦ How big the instruction is in memory, which in turn determines how many clock cycles it takes for the memory to deliver the instruction to the processor. Not all instructions are the same size. ✦ How many operands the instruction has, and where they are located. ✦ How long it takes the memory or I/O channel (and therefore the disk) to deliver those operands to the processor. Chapter 3 ✦ PC Overview 31 ✦ How long the processor actually takes to manipulate the operands and complete the instruction. ✦ How long it takes to put the result where it belongs. Adding the time each of a program’s instructions takes then tells us how long the program takes to run, which is a measure of performance. Buses Buses are wires that computer chips operate according to an agreement (called a protocol) for how every chip connected to the bus must behave. A bus con- nects the processor to each of the other components, but there are other buses elsewhere in your PC. The bus wires themselves carry signals among the chips, communicating what the other component should do, an address for where within the component the function should be carried out, and the information being transferred. Because bus cycles move information from one place to another, there are always two players in every bus cycle, and the cycle itself is very much like a conversation. Let’s listen in on one conversation between your processor and memory: Processor: Memory, I’d like the number at address 77349. (Pause while the memory works.) * * * Memory: Here it is. The number stored there was 42. That conversation represents the processor reading memory. The processor can also write to memory, which involves a conversation like this: Processor: Memory, store a number at address 77349. Processor: Memory, the number to store is 100250. (Pause while the memory works.) * * * The memory is silent throughout that last conversation, never replying that it has actually received the information and completed its work. The buses in PCs rely on the assumption that the source will get the data there in time. If not, the destination picks up garbage. Your computer crashes at best, but at worst silently corrupts some calculation or stored value. There are several distinct buses inside your PC, not just one, each designed for a particular purpose: ✦ Front side bus — The front side bus (FSB) connects the processor to a chipset, one or two chips responsible for joining all the different buses together. The two major processor manufacturers, Intel and AMD, each use a different design for the FSB. Because of that, you can’t directly plug an Intel chip into an AMD socket, and vice versa. ✦ Memory bus — The memory bus connects the chipset to the mem- ory modules. Current technology memories use bus designs called 32 Part I ✦ Introduction Double Data Rate (DDR) Synchronous Dynamic Random Access Memory (SDRAM) or RAMBUS; somewhat older designs use Single Data Rate (SDR) SDRAM. ✦ Graphics bus — All high performance graphics chips interface to the chipset through an Accelerated Graphics Port (AGP) bus. ✦ Expansion bus — The expansion bus connects adapter cards and I/O buses to the chipset. As of late 2003, all PCs used the PCI bus to implement the expansion bus, but within a few years, the newer PCI Express bus will replace PCI. Figure 3-5 shows how the buses connect. The chipset in Figure 3-5 is a compos- ite of what’s labeled the Northbridge and Southbridge chips, a common PC design. There’s another bus between the Northbridge and Southbridge chips, one typically proprietary to the chipset manufacturer. Figure 3-5: PC bus interconnections Processor Memory Front side bus Memory bus AGP bus NorthbridgeGraphics Southbridge Internal chipset bus Expansion bus Chapter 3 ✦ PC Overview 33 Memory PC memory comes mounted on printed wiring modules, as shown in Figure 3-6. Figure 3-6: PC memory ©2004 Barry Press & Marcia Press If you’ve ever seen one of the old pigeonhole desks with rows of compart- ments to sort letters into, you’ve got a picture of how memory is organized in your computer. Figure 3-7 shows the idea — a memory in a PC is a collection of places to store numbers, each with its own unique address. Although every- thing stored in memory is just a number, the interpretation of each number depends on the program that owns the information. The number 42 stored in address 3 in Figure 3-7 could be part of an instruction to the processor, part of your address on a network, part of your address at home, a count of eggs you own (meaning that you likely have more than enough in the refrigerator), part of a bigger number that’s the cost of last night’s pizza, one dot in a drawing, the character B in “HAPPY BIRTHDAY,” or a lot of other things. Memory loca- tions don’t care what the meaning of the number they store is, only that the number needs to be faithfully stored and retrieved on request. Numbers stored in individual bytes in memory range from 0 to 255 (which is what can be represented by the 8 bits in each byte). That’s not enough to do everything you use a computer for. If the computer has to remember that you have thousands of paper clips in inventory, it has to store that number in at least two memory locations. Most PC processors are designed to operate on 4 bytes (32 bits) at a time, so programs for those processors store most num- bers as 32-bit values. If the first byte holding your paper clip inventory is at address 102916, locations 102916 through 102919 hold the entire number. The same idea is true for instructions, which can require 1, 2, or more bytes to hold. Any time the processor references the first byte of a number or instruc- tion, it references all of them. 34 Part I ✦ Introduction Figure 3-7: Memory is a bunch of compartments. Each one stores a number. Making the bus wider improves performance because the processor is likely to read all 4 bytes of a number if it reads any of them. Strings — a group of char- acters in order, one following another — are common exceptions to storing information in 32-bit chunks, but because strings are so often at least several characters long, very little of the effort in retrieving four characters (4 bytes) at a time goes to waste. Your PC uses memory modules made from several memory chips. It’s built that way because memory chips themselves are commonly only a few bits wide. The memory module operates the individual chips in parallel. The key parameters defining a memory module are these: ✦ Capacity — A memory module holds a specified number of bytes, with one address corresponding to each byte. The capacity of a memory module is the number of bytes it holds. ✦ Width — A memory module built from multiple chips in parallel can be as wide as the module designer wants, with the width being the number of bits (8 to a byte) that the memory accesses at one time. Common widths for memory modules used in current computers are 32, 36, 64, and 72 bits, depending on whether or not your computer checks data transfers from memory for reliability. Don’t confuse the bit width of memory with the number of pins on the module because there are also pins for power and control. Common pin counts are 30, 72, and 168. 75 0 1 2 3 4 5 6 7 8 9 10 11 189 63 42 1 15 71 2 2 0 249 4 0 12 Memory is a collection of places to store numbers. Each place, called a memory location, is one byte. One memory location stores one value. That value can be anything in the range from 0 to 255. Each memory location stores a physically different number, although the same value can be stored in different locations any number of times. Every memory location has an address, which is a unique number assigned to it and no other location. When the processor wants to read or write the value in a specific location, it tells the memory the address of the location. Addresses usually start at zero and continue up from there. Chapter 3 ✦ PC Overview 35 [...]... 3.516 1 ,28 0 768 1.667:1 983,040 0.938 1.875 2. 813 3.750 1 ,28 0 960 1.333:1 1 ,22 8,800 1.1 72 2.344 3.516 4.688 1 ,28 0 1, 024 1 .25 0:1 1,310, 720 1 .25 0 2. 500 3.750 5.000 1,360 768 1.771:1 1,044,480 0.996 1.9 92 2.988 3.984 1,600 900 1.778:1 1,440,000 1.373 2. 747 4. 120 5.493 1,600 1, 024 1.563:1 1,638,400 1.563 3. 125 4.688 6 .25 0 1,600 1 ,20 0 1.333:1 1, 920 ,000 1.831 3.6 62 5.493 7. 324 1, 920 1,080 1.778:1 2, 073,600... resources and work are involved Table 3-1 Resolution, Colors, and Display Memory Size Display Memory Size (Megabytes) vs Color Depth Display Characteristics Width Height Aspect Ratio Pixels 8 Bit 16 bit 24 bit 32 bit 800 600 1.333:1 480,000 0.458 0.916 1.373 1.831 1, 024 768 1.333:1 786,4 32 0.750 1.500 2. 250 3.000 1,1 52 864 1.333:1 995, 328 0.949 1.898 2. 848 3.797 1 ,28 0 720 1.778:1 921 ,600 0.879 1.758 2. 637... 1.831 3.6 62 5.493 7. 324 1, 920 1,080 1.778:1 2, 073,600 1.978 3.955 5.933 7.910 1, 920 1 ,20 0 1.600:1 2, 304,000 2. 197 4.395 6.5 92 8.789 1, 920 1,440 1.333:1 2, 764,800 2. 637 5 .27 3 7.910 10.547 2, 048 1,536 1.333:1 3,145, 728 3.000 6.000 9.000 12. 000 Aspect ratio is the ratio of the display width in pixels to the height The standard PC aspect ratio is 1.333:1, also expressed as 4:3 HDTV monitors use an aspect... less demanding on the motherboard and memory ✦ You pay a premium to upgrade Replacing the processor to upgrade it may require replacing the motherboard and possibly the memory, and so may be more expensive than just swapping a chip Overall, you need to decide how much performance you need and what you’re willing to pay for it You’ll use the processor for several years, and you can expect the demands your... For example, suppose you have a disk guaranteed to have 23 4,441,648 sectors Multiplying times 5 12 bytes per sector shows that the disk contains 120 ,034, 123 ,776 bytes Disks are sold as if 1 gigabyte contains 1,000,000,000 bytes, so your 120 ,034, 123 ,776-byte disk is sold as having 120 GB capacity In Windows, however, 1 gigabyte contains 1,073,741, 824 bytes, so in Windows Explorer the disk is shown with... the display memory means you get more information in and out The highest-performance display cards today are ones using the 8X AGP bus, which at peak rates can transfer a whopping 21 33MB per second The 8X AGP standard replaced the 4X (1066MB per second), 2X (533MB per second), and 1X (26 6MB per second) versions of AGP, which in turn replaced the PCI bus (133MB per second peak) for video cards ✦ Delegate... 5 Buses, Chipsets, and Motherboards ✦ ✦ ✦ ✦ 4 Processors, Cache, and Memory C H A P T E R ✦ ✦ ✦ ✦ In This Chapter T he first step in understanding the performance you get from a processor and how the processor relates to the bus and to memory is to look closely at what the processor does, which is to execute instructions Understanding the instruction execution cycle leads to understanding what engineers... system The PC you’ll see how to build in Chapter 25 has eight USB 2. 0 ports, six in back and two in front, convenient for temporarily attaching USB flash memory disks and cameras IEEE 1394 (FireWire, Chapter 5) is less common, but nice to have on the front panel if you have a camera using that interface Motherboards also commonly offer options for audio and Ethernet Both can be added using separate PCI adapter... headaches or make them dizzy, and many people complain about flicker on the screen at update rates of 60 times per second or less A decade ago, games used video resolutions of 320 24 0 at 25 6 colors to limit the work to update the screen to what the processor, bus, and video card could achieve and keep refresh rates up Game designers today assume fast processors, fast buses, and hardware acceleration in... update Updating every pixel of a display set for 128 0×1 024 resolution and 8-bit pixels (25 6 colors) requires that the processor move 1 .25 MB of data into the display memory The processor executes a lot of instructions for every pixel, so in redrawing the screen it executes hundreds of millions of instructions If all the data the processor needs is in memory, and if you’re running a processor capable of billions . 921 ,600 0.879 1.758 2. 637 3.516 1 ,28 0 768 1.667:1 983,040 0.938 1.875 2. 813 3.750 1 ,28 0 960 1.333:1 1 ,22 8,800 1.1 72 2.344 3.516 4.688 1 ,28 0 1, 024 1 .25 0:1 1,310, 720 1 .25 0 2. 500 3.750 5.000 1,360. 16 bit 24 bit 32 bit 800 600 1.333:1 480,000 0.458 0.916 1.373 1.831 1, 024 768 1.333:1 786,4 32 0.750 1.500 2. 250 3.000 1,1 52 864 1.333:1 995, 328 0.949 1.898 2. 848 3.797 1 ,28 0 720 1.778:1 921 ,600. 0.996 1.9 92 2.988 3.984 1,600 900 1.778:1 1,440,000 1.373 2. 747 4. 120 5.493 1,600 1, 024 1.563:1 1,638,400 1.563 3. 125 4.688 6 .25 0 1,600 1 ,20 0 1.333:1 1, 920 ,000 1.831 3.6 62 5.493 7. 324 1, 920 1,080