Section 6.2. Hardware Design Criteria


6.2. Hardware Design Criteria

With the functional requirements determined, the next step was to establish design criteria for the media center PC hardware. The table to the right shows the priorities we assigned for the media center PC.

DESIGN PRIORITIES

Price

Reliability

Size

Noise level

Expandability

Processor performance

Video performance

Disk capacity/performance



Here's the breakdown:


Price

Price is an issue in that we'd like the total price of the system to be lower than that of a commercial Windows MCE system with similar functionality, or, alternatively, that the price be the same but the functionality of our system be higher. Accordingly, we'll use only first-rate components in this system, and if spending a few extra dollars buys us additional performance, reliability, or functionality, we'll spend the extra money.


Reliability

Reliability is important for this system. Not, perhaps, in the same sense that reliability is critical for a departmental file server, but Robert never wants to have to explain to Barbara why our fancy new media center PC failed to record a program she was looking forward to watching. We won't use RAID disk storage, ECC memory, and other server technologies for cost, space, and other reasons, but we will attempt to design as reliable a system as possible within those constraints by using top-notch components, emphasizing cooling even at the expense of noise level, using an oversize power supply, and so on.

Running Your Own TV Station

If you want to distribute RF throughout your home, you can do so by using an RF modulator. In theory it is possible to distribute that signal on the existing cable by filtering the channel used by the RF modulator at the cable demarc, but in practice attempting to do so risks poor image quality and interference on that channel, not just for you, but for your neighbors. If that happens, expect a visit from an angry cable company employee.

The alternative, which we would choose, is to run a separate coax cable to each TV and provide some means of switching between the two RF inputs. We decided that wasn't worth the trouble. It's easier just to transfer video files, either on a DVD or across the network to a set-top PC connected to the remote TV.



Size

Size is relatively unimportant for our media center PC, but we would like it to resemble a standard home-audio component in size, shape, and appearance. Accordingly, rather than simply using the smallest available case, we evaluated cases that were designed for use as media center PCs.

DEPTH MATTERS

Many media center PCs have been built in standard mini-tower cases, and we've even seen one or two in full-tower cases standing beside the television. If your media center PC is to reside in an entertainment center, make sure that the case you use fits. In particular, if your entertainment center has an enclosed back, make sure the case is not too deep to fit.

Ron Morse adds that in addition to case dimensions, you need to allow for the big, fat, long video connector and its thick cable, and the AC power cord, too. Also, many media center PC cases exhaust warm air through side or top vents, so to prevent overheating it's important to maintain an inch or more of clearance near those vents.



Noise level

Perhaps surprisingly, noise level is only moderately important for our media center PC. That's true because this system is destined to reside in an entertainment center across the room from the sofa. When the system is being used to view a movie or listen to music, even moderately loud system noise is swamped by the sound coming from the speakers. Of course, the system is not always active, so it must be reasonably quiet to avoid interfering with other uses of the room. Achieving low noise levels always involves trade-offs among cost, performance, cooling, and reliability. All other things being equal, a quiet system costs more, is slower, runs hotter, or is less reliable (or all of those.) Accordingly, we decided to compromise by using quiet standard components, but not by using radical quiet-PC technologies such as a very slow processor, an insulated enclosure, fanless coolers, water cooling, and so on.


Expandability

Expandability is moderately important, but only in the sense that we want our system to be easily upgradable to newer technologies like HD-DVD or Blu-Ray. Any new component we install will likely replace an old component, so we have no real need for many spare drive bays, expansion slots, and so on. We want provision for one optical drive and at least two hard drives. We'll choose a motherboard with integrated everything except video, so the only expansion slots we'll need are one PCIe slot for the video adapter and two or three PCI slots for the tuners. We do want to make provision for adding unrelated functions to the system, such as controlling a home weather station or functioning as an automated attendant and voice mail controller for our telephone system, but we can accommodate that requirement by having one or two spare expansion slots.


Processor performance

Processor performance is moderately important. Simple functions such as playing a CD or DVD or playing recorded video are undemanding; the slowest mainstream processor is more than sufficient for such functions. Recording video is a different matter, because real-time video compression is extremely CPU intensiveparticularly HD videobut we intend to use analog tuners with hardware compression support and a digital tuner that offloads compression duties to the video adapter GPU. But we still need a capable processor because the media center PC will at times function as a normal PCfor gaming, web browsing, and so onand we want to build the system initially with enough processor horsepower to handle an HD-DVD or Blu-Ray optical drive, either of which places heavy burdens on the main system processor.

TECH HELP
Older Standards Make Life Easier

Sometimes the old ways are the good ways, and this is certainly true for someone who wants to build a media center PC. Broadly speaking, there are two types of television signaling protocols and two delivery methods.

The current standard-definition television signaling protocols are NTSC (National Television System Committee), which is used in North America and Japan, and PAL (Phase Alternating Line), which is used in most of Europe, China, and Africa. NTSC and PAL are analog protocols. They may be transmitted over-the-air or via cable using analog transmission or via cable or satellite using digital transmission. The second type of signaling protocol used in the United States is called ATSC (Advanced Television Systems Committee). ATSC is comparable to the DVB (Digital Video Broadcasting) standard used in Europe and the ISDB (Integrated Services Digital Broadcasting) standard used in Japan. ATSC is purely digital and may be transmitted over-the-air or via cable or satellite, using digital transmission methods. Although Digital Television (DTV) and HDTV (High-Definition Television) are inextricably linked in the public mind, ATSC standards also define standard-definition DTV modes.

There are several other standards in limited use. France uses SECAM (a French acronym for Sequential Color with Memory). Brazil uses a hybrid of NTSC and PAL called M-PAL. Argentina, Paraguay, and Uruguay use a lower bandwidth version of PAL called N-PAL. Many former Soviet-bloc and Middle Eastern countries use a variant of SECAM called MESECAM. But if you're reading the English-language version of this book, you're almost certainly using NTSC or PAL, and most capture cards are available in versions for either of those standards.

Although digital transmission and HDTV have real advantages in terms of bandwidth and image quality, both have severe drawbacks for anyone contemplating building a media center PC. A standard NTSC signal delivered by analog cable is easy for a media center PC to deal with. You can simply connect the cable to the tuner card and allow the PC to change channels as needed.

Using digital cable or satellite as a program source makes matters more complex. Although digital tuner cards for PCs exist, various laws and differing cable/satellite standards limit their utility. A digital tuner card can freely tune OTA digital broadcasts (standard-definition or high-definition), but probably cannot tune digital signals supplied by cable or satellite, unless those signals are unencrypted (rare) and use a standard modulation method such as QAM-64 or QAM-256.

In practical terms, if your signal source is digital cable or satellite, you will probably be limited to using the satellite receiver or digital cable box to tune the signal. To record programs on different channels, you must change channels on the satellite box or digital cable receiver rather than on the media center PC. That makes it difficult, although not impossible, to select the channel to be recorded under programmatic control.

Some satellite receivers and digital cable boxes are programmable to change channels at specific times. If you have such a box, programming recordings becomes a two-step process: program the cable/satellite box to tune the proper channel at the proper time, and program the media center PC to begin recording at that time on the output channel of the cable/satellite box. If you don't have a programmable cable/satellite box, the best solutions to the digital tuning problem are Rube Goldberg arrangements.

One solution is a programmable remote control for your satellite receiver or digital cable box. To record a program, you set the remote control to change to the proper channel at the proper time and leave it pointed at the satellite receiver or digital cable box. You also set the media center PC to begin recording at the proper time. The media center PC records whatever signal the satellite box or digital cable box happens to be delivering, so if someone moves the remote or the dog walks in front of it at just the wrong time, you may end up recording something other than what you intended.

Another solution is to equip the media center PC with an IR emitter that can mimic the remote control for your satellite receiver or digital cable box. The IR emitter works under control of a scheduling program running on the media center PC. When it's time to record a program, the media center PC sends a series of commands to the IR emitter, which turns on the satellite receiver or digital cable box and tunes it to the correct channel.

Either of these methods is awkward at best, but some solutions, such as the IR Blaster described later in this chapter, are reported to work well enough to get the job done.



Video performance

Video performance is moderately important overall, but there are several aspects of video performance in a media center PC that must be considered individually. Video capture quality is critical, so it's important to choose tuner/capture cards with excellent native video quality. Video playback quality is also critical, but any decent video adapter can easily handle video playback. When the media center PC is being used as a PCas for browsing the Web or checking email2D display quality is important, particularly because even high-definition televisions are not designed to be used as computer displays. Fortunately, the nVIDIA video adapters that are required to assist the HDTV tuner card in compressing the video stream also have excellent image quality when a television is used as the display. The final aspect of video performance is 3D acceleration for gaming. Our media center PC will be used for only casual gaming, so very high 3D graphics performance is unnecessary.


Disk capacity/performance

Disk capacity and performance are moderately important. Years ago, we'd have ranked these aspects as critically important, because hard drives of the time were smaller and slower than today's models. Fortunately, current hard drives have huge capacities and even mainstream models are fast enough to keep up with the demands of a media center PC. At first glance, capacity might seem more important than performance, but in fact both are equally important. On a lightly loaded media center PC, even a slow, 5,400 RPM "near-line" drive might be fast enough. But our system is designed to support many activities concurrently, all of which require disk access. For example, our system might have to play back one analog stream while it records a second stream on the second analog tuner while it records a third stream on the digital tuner while it streams audio to Barbara's office. To make sure the drive can keep up without dropping any frames, we'll choose a 7,200 RPM S-ATA drive that supports NCQ (Native Command Queuing) and has a large buffer.




Building the Perfect PC
Building the Perfect PC, Second Edition
ISBN: 0596526865
EAN: 2147483647
Year: 2006
Pages: 84

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