Laptops

Fundamental Principles

Form factors

Laptops or notebooks are small, portable PCs that can be run from built-in batteries.  They typically measure 12–15 inches wide by 8–11 inches, and 1–2 inches in height and weigh around 3–4 kilograms.

Because motherboards and DVD drives need to fit into a compact space most laptop components are custom designed for a model or range of models.  This means that there are very few standard-sized components; replacement parts need to be ordered directly from the manufacturer (often at high cost).

The biggest problem in laptops is dissipating heat.  Modern laptops expel hot air through main vent holes (at the rear or underneath) — which means it is important to ensure that laptops are placed on hard surfaces to ensure an air gap underneath; not on soft surfaces that could block vents.  To reduce noise, temperature-switched fans are used.

Memory

For many years laptop memory was non-standard and needed to be matched specifically to model for fitting and performance.

Modern laptops use standard memory modules such as SO-DIMM (Small Outline DIMM).

SO-DIMMs come in different configurations — 72, 100, 144, or 200 pins — so it is important to select the correct type.  In addition the 200-pin module comes in two varieties: DDR and DDR2, distinguished by notch location.

Hard Drives

Laptops use 2.5" IDE hard disk drives.  These use a 44-pin connector with pins spaced 1mm apart (as opposed to 0.1" on standard 3.5" drives).  Pins 1-40 are identical to standard IDE connections; pins 41-44 are used for power, integrated on the ribbon cable.  Pin 20 may be removed as a 'key'.

These drives are usually housed in small caddies with a quick-release adaptor fitted to the IDE connection.  This allows them to be quickly replaced with a similar model.

CD / DVD and floppy drives

Laptops do not use standard CD / DVD drives or floppy drives but some manufacturers use their own standard fittings to allow drives to be swapped on different models in their range.

Peripherals

Standard ports

Laptops usually have a range of standard ports, including USB, PS/2, VGA graphics, parallel printer, serial (COM), RJ11 (modem) and RJ45 (Ethernet network).

Docking Station / Port Replicator

Some models have a special adaptor socket that allows the laptop to attach to a docking station or port replicator.

A port replicator remains on the user's desktop and allows them to quickly attach the laptop to a range of fixed peripherals, e.g. keyboard, mouse, monitor, printer and network.

Docking stations are identical to port replicators but also have facilities for supporting standard PCI-style expansion cards.

Expansion Slots

PCMCIA

Laptops cannot use standard PC expansion cards so manufacturers developed the "PC Card" (commonly known as PCMCIA) adaptor.

Three types of PCMCIA adapters currently exist:

Type I cards are 3.3mm thick with a single row of pins and work as memory-expansion units.  They are rarely used because PCMCIA memory access is too slow for modern equipment.

Type II cards are 5mm thick.  Most cards are type II, providing a range of functions from network adapter to modem.  Type II slots are backward compatible, so Type I cards will work in them.

Type III cards are 10.5mm thick and are intended primarily for use with removable hard drives.  Both Type I and Type II cards can be used in a Type III slot.

The three card types measure 2.12" × 3.37" and use a 68-pin slide-in socket.  They are hot-swappable.

Most laptops feature a double-Type II slot.  This allows two Type II cards to be inserted, or a single Type III.

CardBus

In 1995 the CardBus (also called PC Bus) card was introduced.  These are similar to PCMCIA cards but are incompatible with (16-bit) PCMCIA due to their 32-bit design.

CardBus sockets are compatible with older PCMCIA cards, but the newer cards are notched so that 32-bit cards cannot plug into 16-bit sockets.

ExpressCard

ExpressCard was introduced in 2004 as a replacement for CardBus.

The card connects internally to the PCI Express channel on the motherboard, giving a dramatic speed increase.  Alternatively, if a designer wishes, the card can connect to the internal USB2 bus.

There are two sizes of card — 75mm × 43mm and 75mm × 54mm; both are physically incompatible with existing PCMCIA slots.

Mini PCI

Mini PCI is an adaption of the standard PCI bus for laptops.  There are three sizes of card (also called types I, II and III but not to be confused with PCMCIA) and they fit inside the case like SO-DIMMs.  There is a similar mini-PCIExpress system available.

Communication

Many laptops feature built-in IrDA infra-red connections and RJ45 Ethernet network connectors.

Some models also feature built-in Wi-Fi and Wi-Max wireless networking, or mobile phone network technology such as GPRS.

Power

Batteries

Laptops use a detachable rechargeable battery.  This battery will vary in size and capacity from model to model.  Replacement cells must match the original specifications or damage may occur.  Laptop batteries typically have a lifespan of a few years and can be expensive to replace.

Older Ni-Cad (nickel-cadmium) batteries can run for a few hours but suffer from 'memory-effect', which reduces charging capacity and lengthens charging time.

Newer laptops use Ni-MH (nickel metal-hydride), Li-ion (lithium-ion), or lithium-ion polymer batteries.  These provide up to two or three hours of operation.  It is best to run the battery until nearly flat and recharge fully before reusing.  It should take a few hours to perform a full recharge.

Laptops have hibernate mode, where memory contents are written to a hard drive file and the system is completely shut down.  When restarted, the hibernated memory contents are restored and normal operation restarts at the place it left off.  These modes are part of the Advanced Power Management (APM) standard.

External power supplies

Laptops can be powered by an external switch-mode power supply (also called switching power supples) that plugs into the commercial mains supply.  Most allow the rechargeable battery to be trickle-recharged while the laptop is in use.  Again, these supplies vary and cannot usually be exchanged between models.

Processors

Power consumption is a major issue in laptops.  Laptop CPUs are designed to use as little electricity as possible, switching automatically into throttled modes to conserve battery power and reduce heat output.

Motherboards in are rarely designed to allow processor upgrades.

Intel's Pentium M and Celeron M are designed specifically for laptops, and the company produces special variants of Core Duo and Core2 Duo aimed at the laptop market.  If these processors are bundled with a specified chipset and wireless network adaptor, Intel calls this a Centrino laptop.

AMD produces Turion 64 and Turion 64 X2 chips aimed at the same market.

Repairing laptops

Tools

Laptops can be fiddly to take apart due to the complexity of their construction.  A technician will typically require a set of jeweller's screwdrivers.  Although most screws will have a Philips-style head, Torx style drivers may also prove useful.

Because laptops have plastic cases it is essential to pay careful attention to anti-static precautions to avoid damaging expensive and difficult-to-replace components.

Diagnostic procedures

Standard steps that might be taken in diagnosing a hardware fault on a laptop are:

• Verify AC power (i.e. check power LEDs, swap AC adapter)
• Verify DC power (use a multimeter)
• Remove unneeded peripherals
• Plug in an external monitor
• Toggle the Fn key settings on the keyboard
• Check whether an LCD cut-off switch has been tripped
• Verify backlight functionality; check display for dead pixels
• Check digitizer pad or stylus issues
• Check all keys on keyboard
• Check antenna wires on wireless adaptors

Non-standard laptops

Tablet PC

Tablet PCs are laptops with touch-sensitive screens, operated by a stylus.

Most models have flip-over screens and the desktop display can be quickly switched from landscape to portrait mode.  The case will also include extra buttons to the side of the screen for quick scrolling or navigation.

Windows XP Tablet PC Edition is XP Professional with added "ink" software for controlling the mouse pointer with a stylus and adding annotation to pages in programs.  It can perform handwriting recognition.

One Laptop per Child project

The One Laptop per Child project was developed to create a cheap laptop that could be supplied to children in developing countries, to give greater access to education.

The $100 laptop (also called XO-1) incorporates wireless networking and a basic LCD display.  It uses an operating system based on Fedora Linux using the single-tasking Sugar desktop (housed in ROM)

The laptop has no hard drive, CD / DVD drive or floppy and will load software directly via its wireless networking link.  Network access can be denied as an anti-theft measure.