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Buying a Computer

CPU

The CPU (Central Processing Unit) or processor is the heart of the computer. There are many different types of CPU's and with different types of speeds. The CPU in a large part, determines how fast the computer will be and what capabilities your machine will have. Over Summer 2005 the school disposed of this last desk top PC with less than 500Hz CPUs..

The processors you will most likely encounter in desktop PCs are the Intel Pentium 4 5xx, 6xx and 8xx, and the AMD Athlon 64 and Athlon 64 X2. These two series of processors represent the performance end of the market; while AMD's Sempron and Intel's Celeron processors are targeted a budget-conscious buyers.

Here's a brief breakdown of the processors on the market:

Intel processors

Last year, Intel changed its processor number scheme, abandoning the MHz rating in lieu of an abstract model numbering scheme. Now Intel processors are arranged in families, such as the 3xx (Celeron), 5xx (Pentium 4), 6xx (Pentium 4 EM64T) and 8xx (Pentium 4 dual-core) families. Within a given family, the higher the number, the faster the processor; for instance the Pentium 4 660 runs at 3.6GHz, while the Pentium 4 630 runs at 3.0GHz. If you find the new numbering scheme confusing, don't worry - most sellers will be more than happy to tell you the MHz speed of any processor they are selling.

Intel has a chart that breaks down the processor numbers on its web site.

The four main families of Intel desktop consumer processors break down as follows:

  • The Celeron (3xx) processors are entry-level CPUs, designed for low-cost systems. They don't have as much internal memory ("L2 cache") as other Intel CPUs.
  • The Pentium 4 (5xx) processors are the mid-range processors. They are faster, on a clock for clock basis, than Celerons, but mostly lack 64-bit extensions. If the last digit is a "1", such as in the Pentium 541, it means the processor actually does have 64-bit extensions.
  • The Pentium 4 EM64T (6xx) processors have 64-bit extensions, similar to those found in the AMD Athlon 64. They're best used with the new 64-bit version of Windows XP, which can make the most of their extra power.
  • The new Pentium 4 dual-core (8xx) range essentially has two 6xx processors on a single packaged chip, effectively making the system a dual-processor system (even though it only has "one" CPU). The Pentium 4 dual-core processors require motherboard with a supporting chipset, such as the Intel 945/955X chipsets.

All of these current Intel processors fit into LGA755 motherboards, although you will need a supporting chipset if you plan to install an 8xx processor.


AMD processors

In its consumer line of products, AMD has boiled its vast collection of different products down into three core models: the Sempron, the Athlon 64 and the Athlon 64 X2. You may still see the rare Athlon XP around, but we recommend avoiding them.

AMD has an unusual naming schema, basing its product names not on the actual MHz rating of the processor, but on the MHz rating of an Intel processor of equivalent speed. For instance, the Athlon 64 3000+ only runs at 2160MHz, but because it is as fast as a 3,000MHz Intel Pentium 4 (because of improved processing efficiency), AMD call it the Athlon 64 3000+. This is done to reduce confusion for buyers deciding whether to buy Intel or AMD. And if you're worried that AMD are highballing their comparative speeds, don't be - if anything, the AMD processor speed equivalents are conservative. As an added bonus, the naming schema aligns the AMD processors, making it easier to choose between different types of AMD processors (for instance, it makes it easier to decide whether to buy Sempron or Athlon 64, because both processors are rated on the same scale).

  • The Sempron is AMD's answer to the Intel Celeron. It's a very low cost processor based on the Athlon XP. It lacks 64-bit extensions. It fits in a Socket 754 motherboard.
  • The Athlon 64 is AMD's mainstream and high-end processor. It has 64-bit extensions (which require a 64-bit version on Windows to make the most of). Some use 754-pin sockets, others 939. Check which you have before buying your motherboard.
  • The Athlon 64 X2 is a dual-core processor, integrating two Athlon 64 CPUs on a single piece of silicon, effectively making it a dual-processor system on a chip. Unlike the Intel dual-core solution, the X2 does not require a special chipset, and should run on any Socket 939 motherboard (although many motherboards will require a software "BIOS" upgrade).


Dual processors and dual-core processors A dual-core CPU

Dual processor motherboards are usually only found in server setups and high-end desktop PCs that use the functionality for intense graphics CAD and design work. Therefore, dual processor boards aren't really applicable to the consumer desktop PC market. However, the recent introduction of dual-core processors by both Intel and AMD is bringing multiprocessing to the masses.

A dual processor system is exactly what the name implies - a system with two processors. You need a motherboard with two processor sockets to make this work (and such motherboards tend to be expensive). A dual-core processor is a little different, however. A dual-core processor is a single chip that has multiple processing "cores" on it. It will appear to the operating system as two processors, act the way two processors would act and have the same kinds of advantages as a dual-processor system has. It is only one chip, however, and only requires a single standard socket on the motherboard.

AMD's Athlon 64 X2 (which has the memory controller on the chip), should work in any Socket 939 motherboard, although most require a BIOS upgrade. Intel 8xx dual-core processors (which leave memory control to the motherboard's chipset) require a supporting motherboard.

By next year, both Intel and AMD expect that the bulk of processors shipped will be dual-core models.


Hyper threading

Hyper-Threading technology is now found in most P4 2.8GHz and above chips, but was initially introduced to desktop PCs through the newer P4 3GHz in early 2003. Hyper-Theading is a technology developed by Intel to improve the performance of the processor by increasing its efficiency. It does this by pretending that it's two processor instead of one, so the operating system throws more work at it. It's not to be confused with dual-core processor however - a Hyper-Threading processor still only has one core; it's just pretending that it has two.

Some Intel processors are both Hyper-Threading and dual core, and will thus appear as four processor to the operating system.

Summary

What does this all mean and what is right for you? You should compare this with buying a car. If you do not need the speed, why would you buy a Porsche? If you can do with a Ford why buy a Rolls Royce?

The school currently uses Windows XP and Office XP for its work, students will thus fin it easier of that is what they have at home. Almost any new computer will run these packages adequately there is no need to spend a fortune

Recommended CPU: Intel Celeron or based computers for the more cost conscious, Pentium 4 or AMD Athlon XP for the power user. Current new desktop systems are no slower than 1.3 GHz.

Memory

Buying system memory (RAM) for the computer is important for the overall performance of the computer. Programs are loaded from the hard disk and stored into the computer's memory upon usage. Whenever a program is stopped, the program is stored from memory back to the hard disk again.
Not enough system memory will result in a state called swapping. This means that the hard disk will be used as additional memory, but since a hard disk uses mechanical parts, the overall performance of the computer will degrade.

A stick of ramThe most commonly used type of RAM in PCs is Double Data Rate (DDR) SDRAM. Single Data Rate (SDR) SDRAM is still available for older systems is becoming increasingly rare. SDRAM also differs in the physical sense, SDRAM DIMMs will not physically fit into a DDR RAM slot and visa versa. Both are implemented into the system as DIMMs (Dual Inline Memory Modules). DDR memory will always give your system or graphics card better performance than SDR memory. This is because DDR, or double data rate RAM, sends two data bits on every clock pulse. DDR II memory has also been recently released with improved speeds and heat spreaders to keep the memory cool.

DIMMs come in different flavours - PC100 and PC133 for SDRAM, and PC2100, PC2700, PC3200, PC4000, PC4400 for DDR SDRAM. DDR II RAM is also available from PC3200 up to PC6400. The numbers relate to the speed at which the memory modules can operate (although the DDR numbers use a different measuring system, so it is impossible to compare the two types of memory through listed speeds alone). Your motherboard must support the type of memory you want to use. Currently only some Intel boards use DDR2.

More memory makes your computer faster too. To go from 64 MB to 128 MB will cost you about £20 and will increase the performance of your machine if you intend to have high usage.

Recommended Memory. 256 MB - 1024 MB for all new computers. Memory is relatively cheap right now, so there is no reason not to have the added speed and convience of 512 MB of system RAM.

Hard Disks

With the hard disk, both speed and size matters. In terms of the brand, I would personally stick with the leading brand names like IBM, Seagate, Western Digital. I wont buy Maxtor. With hard disks there are basically four different types, EIDE, SCSI interface, Firewire, or USB.
For SCSI and firewire drives, you need a separate interface card and the hard drives themselves are more expensive, but faster then EIDE drives.
Within EIDE you have three different types, regular EIDE, Ultra DMA and Ultra ATA. The difference is that Ultra DMA and ATA have higher speed in terms of accessing and data transfer since the hard disk runs faster (DMA 5400 RPM, ATA 7200 RPM) and because of a special interface the data transfer rate is higher (66 MB/sec, 100 MB/sec, or 133 MB/sec). The access to data on the disk (seek time) is very important for the overall performance of the computer. Data transfer rate is important if you are using big files like big databases or video files. Hard drives are relatively cheap.

Recommended hard disk: 40 - 120 GB, 7-9 ms seek time, 7500 RPM, ATA 100 or 133.
   

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