Divide the hardware specs. into categories, choose what is important to you & then shop around.
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Screen: TFT or Passive/HPA/dual scan.
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TFT is best but needs a little more current. The passive has ghosting so not good for video/games BUT not as quite so high a current draw.
Screen size can vary from 10" for ulraportables to about 15" for desktop replacements. Common resolutions varying from 800x600, 1024x768, 1260(?)x1024 or even 1600x1400 (mmmmm. Dell has it.....I want it!).
I find 1024x768 on a 13.3" screen perfectly readable. Better than a 15" CRT. LCD screens are only really useable at their native resolution. Anything else & the image looks odd.
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Processor: P3, P4, Athlon, Celeron or Duron
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Generally AMD's Athlon competes against Intel's P3 & P4, AMD's Duron against Intel's Celeron.
Make sure you get a mobile version of the processor & not a standard desktop version. The mobile versions require less power.
According to various PC magazines Athlon is faster than P3 & P4 (even thought the P4 may have greater clock speed) and is much cheaper. P4 is new & very expensive. Not sure if there is a mobile version available yet (I *don't* mean a standard P4 used in a laptop).
Ditto Duron against Celeron
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Memory: Usually SDRAM in 168 pin SO-DIMM format
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Typically there are only two memory slots. To provide for future memory upgrades make sure that you get memory on as few modules as possible eg 128Mb on a single SO-DIMM, not 2 x 64Mb SO-DIMMs.
Also make sure you get 133MHz memory. This will work with a machine that requires 66 or 100MHz memory the slower memory won't work with a machine that requires the faster.
Having faster memory may let you use it in your follow on machine whereas a slower type is almost guaranteed to have been superceded.
Common SO-DIMMS are 32, 64, 128, 256Mb. 512Mb is just becoming/about to become available.
Notebook memory is more expensive than for a desktop.
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Battery: Lithium Polymer, Lithium Ion, Nickel Metal Hydride, Nickel Cadmium.
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These are listed in highest to lowest preference for charge capacity.
NB: Lion can't be recharged quite as often as NiMH but isn't supposed to have the memory effect & can carry a greater charge.
NiMH has a smaller memory effect than NiCad & carries a greater charge.
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Hard Disk: Notebook HD are a 2.5" form factor with heights of 8, 9.5, 12.5 or even 19mm (very old, the 19mm ones).
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8mm HD go up to about 20Gb
9.5 to about 30 Gb
12.5 to about 48 Gb
All laptop drives are more expensive, Gb for Gb, than desktop equivalents.
Make sure you check what height drive your laptop can take eg mine can only use 8 or 9.5 mm height drives.
Upgrading is usually very easy: Remove the the HD tray, swap new for old & re-insert tray.
The old HD can be installed in a caddy that can be accessed via the PC-Card slot. All self contained & powered via the slot. It's great for back ups.
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I/O ports: Serial, parallel, USB, Firewire/i-Link, PC-Card/PCMCIA (+ one card slot with Zoomed Video ability), RJ11 (modem) & RJ45 (ethernet), PS/2 mouse/keyboard
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Serial: Not really needed anymore so not too great a problem if it isn't fitted.
Parallel: Again, becoming less important now that printers are being released with USB interfaces.
USB: Very important. Consider getting a laptop with the newer USB 2.0 specification to provide a margin of future proofing. Also consider how many USB ports are fitted. I consider two to be the minimum.
Firewire/I-Link: Mandatory for your video intentions!
Note: Firewire cards are available in PC-Card format for about 80 to 100 quid so you could always buy a PC-Card to provide Firewire ability. You will need a laptop with PC-Card & not PCMCIA slots.
PC-Card/PCMCIA: PCMCIA is the older variant. It's a 16 bit/8MHz ISA bus interface ie the same as a legacy ISA slot in a desktop. PC-Card is the newer version. It's a 32 bit/32MHz PCI bus interfaceie the same as the PCI slots in a modern desktop.
A PC-Card slot is backwards compatible with PCMCIA cards but a PCMCIA slot can't use PC-Cards. PC-Cards operate at 3.3V, PCMCIA at 5V. The PC-Card slot can recognise the type of card & provide the correct power & interface.
Just about every adapter card that is available for a desktop is available for laptops in the PC-Card or PCMCIA interface, albeit at a higher cost.
Some things are available for laptops that aren't available for desktops (without a PC-Card adapter) eg GPS cards, combined networking/fax/modems.
Note: You will need a PC-Card (not PCMCIA) slot to get full 100Mbit networking speed if you use a PC-Card networking card.
Zoomed Video: Usually a capability built into one of the PC-Card slots (not PCMCIA). A zoomed video card takes the video processing load off the processor & has direct access to memory so speeds the processing up a bit. Makes playing DVDs smoother at higher frame rates.
RJ11: Will be built in if the laptop has it's own internal modem. This plug is the US/Oz/Canada/other advanced countries standard telephone plug. UK uses a different plug but no laptop or modem uses it. Instead the cable is terminated at one end with a UK specific plug. Or you can buy an adapter.
Note: Some internal modems are 'Winmodems' ie they aren't really modems. They use the laptop processor + Windows software to emulate a real modem. These types usually can only be used under the Windows operating system.
RJ45: This is the standard ethernet plug for twisted pair wires although there are some ethernet standards that uses coaxial cabling. If your laptop has one then it has an internal ethernet card in it. 100Mbit ethernet is faster than the older 10Mbit ethernet standard.
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Spindles: Refers to the number of spinning storage device compartments ie Floppy disk, CD-ROM/DVD, HD.
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Mine is a 3 spindle machine with 3 separate places for floppy, DVD & HD.
Some machines require you to swap floppy with CD-ROM, or use one via an external interface.
Your optical storage options can include CD-ROM, DVD, CD-RW or combined DVD/CD-RW.
Some machines have provision for a versatile bay that can take some combination (in turn) of additional battery, optical device, Zip drive, additional HD etc etc.
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Pointing device: Only really two options built in --> Touch pad &/or pointing stick/nipple. Some older types or oddities may use a track ball but they're rare now.
IBM & Toshiba only seem to use the pointing stick/nipple.
Most others use a touch pad. Dell have a model that uses both.
A touch pad is my much, much preferred device although there are times when a pointing stick would have been good.
Hope this helps.