types parts and features

Most modern laptops feature 12 inch (30.5 cm) or larger active matrix displayswith resolutions of 1024×768-pixels and above, and have a PC Card (formerly PCMCIA) or ExpressCard expansion bay for expansion cards. Internal hard disks are physically maller –2.5 inch (6.25 cm)– compared to the standard desktop 3.5 inch (9 cm) drive, and usually have lower performance and power consumption. Video and sound chips are usually integrated. This tends to limit the use of laptops for gaming and entertainment, two fields which have constantly escalating hardware demands.[citation neede] However, higher end laptops can come with dedicated graphics processors, such as the Dell Inspiron E1505 and E1705, which can be bought with an ATI Mobility Radeon X1300 or similar. These mobile graphics processors tend to have less performance than their desktop counterparts, but this is because they have been optimized for lower power usage.
There is a wide range of laptop specific processors available from Intel (Pentium M, Celeron, Intel Core and Intel Core 2) and from AMD (Athlon, Turion 64, and Sempron) and also from VIA (C3 and C7-M). Motorola and IBM developed and manufactured the chips for the former PowerPC-based Apple laptops (iBook and PowerBook). Generally, laptop processors are less powerful than their desktop counterparts, due to the need to save energy and reduce heat dissipation. However, the PowerPC G3 and G4 processor generations were able to offer almost the same performance as their desktop versions, limited mostly by other factors, such as the system bus bandwidth; recently, though, with the introduction of the G5s, they have been far outstripped. At one point, the Pismo G3, at up to 500 MHz, was faster than the fastest desktop G3 (then the B&W G3), which ran at 450 MHz.
Some parts for a modern laptop have no corresponding part in a desktop computer:
Current models use lithium ion and more recently lithium polymer batteries, which have largely replaced the older nickel metal-hydride technology. Typical battery life for most laptops is two to five hours with light-duty use, but may drop to as little as one hour with intensive use. Batteries gradually deteriorate over time and eventually need to be replaced in one to five years, depending on the charging and discharging pattern.

A memory chip removed from a high-performance Alienware laptop
Docking station became common laptop accessories in the early 1990s. They typically were quite large and offered 3.5" and 5.25" storage bays, one to three expansion slots (typically AT style), and a host of connectors. The mating between the laptop and docking station was typically through a large, high-speed, proprietary connector. The most common use was in a corporate computing environment where the company had standardized on a common network card and this same card was placed into the docking station. These stations were very large and quite expensive. As the need to additional storage and expansion slots became less critical because of the high integration inside the laptop itself, the emergence of the Port Replicator as a major accessory commenced. The Port Replicator was often a passive device that simply mated to the connectors on the back of the notebook and allowed the user to quickly connect their laptop so VGA, PS/2, RS-232, etc. devices were instantly attached. As higher speed ports like USB and Firewire became commonplace, the Port Replication was accomplished by a small cable connected to one of the USB 2.0 or FireWire ports on the notebooks. Wireless Port Replicators followed.
Virtually all laptops can be powered from an external AC converter. This device typically adds half a kilogram (1 lb) to the overall "transport weight" of the equipment.
A pointing stick or touchpad is used to control the position of the cursor on the screen. The pointing stick is usually a rubber dot that is located between the G, H and B keys on the laptop keyboard. To navigate the cursor, pressure is applied in the direction intended to move. The touchpad is touch-sensitive and the cursor can be navigated by moving the finger on the pad.
Intel, Asus, Compal, Quanta and other laptop manufacturers have created Common Building Bloc standard for laptop parts.
Disadvantages

Standardization issues
While there are accepted world standards of form factors for all the peripherals and add-in PC cards used in the desktop computers, there are still no firm worldwide standards relating to today's laptops' form factors internally, such as supply of electric voltage, motherboard layouts, internal adapters used in connecting the hard disk, optical drive, LCD cable, keyboard and floppy drive to the main board. Most affected by this are uneducated users, especially if they attempt to connect their laptops with incompatible hardware or power adapters.
Laptops are more complex than simple-to-use consumer electronics. A large number of different parts with similar functions may cause some difficulties to repair technicians, as they have to familiarize themselves with different sets of hardware, but this is part of the job in a specialized trade.

Compatibility issues
Any current compatibility problems in the laptop trade are reflective of the early era of personal computers, when there were many different manufacturers, each and every one of them having their own systems and incompatibility was more a norm.
Some mostly internal or proprietary parts made by laptop producers aren't interchangeable with other manufacturers' products, so that the same manufacturer's components are used with the laptop they produced. Some of the reasons for this are to ensure product stability, prolong product lifetime, to avoid dubious warranty issues and to protect computer beginners from harming their machines.
A significant point to note is that the vast majority of laptops on the market are manufactured by a small handful of ODMs.[] The ODM matters more than the OEM. Major relationships include:
Quanta sells to (among others) HP/Compaq, Dell, Toshiba, Sony, Fujitsu, Acer, NEC, Gateway and IBM - note that Quanta is currently (as of August, 2007) the largest manufacturer of notebook computers in the world
Compal sells to Toshiba, HP/Compaq, Acer, and Dell
Wistron sells to HP/Compaq, Dell, IBM, NEC, and Acer
Arima sells to HP/Compaq, NEC, and Dell
Uniwill/ECS sells to IBM, Fujitsu, and Dell
Asus sells to Apple (iBook), Sony, and Samsung
Inventec sells to HP/Compaq, Toshiba, and BenQ
To compensate, some manufacturers have and have had product lines where they have refrained from including some internal hardware in their products by adding in the number of standard hardware outlets and ports, thereby letting users choose their own hardware that they can connect.
In terms of hardware components standardization, PCMCIA/CardBus has proved to be a rather enduring standard. Older laptops lacking a USB port can have a PCMCIA USB/FireWire adapter plugged in. Modern adapters have two to four USB ports or they can be USB/Firewire combo adapters. Thus, such compatibility problems with getting hardware and peripherals connected has nowadays become a non-issue.

Upgradeability
Laptops' upgradeability is severely limited, both for technical and economic reasons. As of 2006, there is no industry-wide standard form factor for laptops. Each major laptop vendor pursues its own proprietary design and construction, with the result that laptops are difficult to upgrade and exhibit high repair costs. With few exceptions, laptop components can rarely be swapped between laptops of competing manufacturers, or even between laptops from the different product-lines of the same manufacturer. Standard feature peripherals (such as audio, video, USB, 1394, WiFi, Bluetooth) are generally integrated on the main PCB (motherboard), and thus upgrades often require using external ports, card slots, or wireless peripherals. Other components, such as RAM modules, hard drives, and batteries are typically user-upgradeable.
Many laptops have removable CPUs, although support for other CPUs is restricted to the specific models supported by the laptop motherboard. The socketed CPUs are perhaps for the manufacturer's convenience, rather than the end-user, as few manufacturers try new CPUs in last year's laptop model with an eye toward selling upgrades rather than new laptops. In many other laptops, the CPU is soldered and non-replaceable. [4]
Many laptops also include an internal MiniPCI slot, often occupied by a WiFi or Bluetooth card, but as with the CPU, the internal slot is often restricted in the range of cards that can be installed. The widespread adoption of USB mitigates I/O connectivity to a great degree, although the user must carry the USB peripheral as a separate item.
NVidia and ATI have proposed a standardized interface for laptop GPU upgrades (such as an MXM), but again, choices are limited compared to the desktop PCIe/AGP after-market.
On January 2007, Asus announced XG Station external video card for laptops. XG Station is connected to the laptops using USB-2 and Express card interface.
On February 2007, there is a new standard for external PCI Express cable and connector. Future laptops can be expanded using external PCI Express backplane and chassis.

Performance

A modern mid-range HP Laptop. It is best used as a desktop replacement
For a given price range (and manufacturing base), laptop computational power has traditionally trailed that of desktops. This is partly due to most laptops sharing RAM between the program memory and the graphics adapter. By virtue of their usage goals, laptops prioritize energy efficiency and compactness over absolute performance. Desktop computers and their modular components are built to fit much bigger standard enclosures, along with the expectation of AC line power. As such, energy efficiency and portability for desktops are secondary design goals compared to absolute performance.
For typical home (personal use) applications, where the computer spends the majority of its time sitting idle for the next user input, laptops of the thin-client type or larger are generally fast enough to achieve the required performance. 3D gaming, multimedia (video) encoding and playback, and analysis-packages (database, math, engineering, financial, etc.) are areas where desktops still offer the casual user a compelling advantage.
With the advent of dual-core processors and perpendicular recording, laptops are beginning to close the performance gap with PCs. Intel's Core 2line of processors is efficient enough to be used in portable computers, and many manufacturers such as Apple and Dell are building Core 2 based laptops. Also, many high end laptop computers feature mobility versions of graphics cards, eliminating the performance losses associated with integrated graphics.
Health issues

Laptop coaster preventing heating of lap and improving laptop airflow.
A study by State University of New York
researchers says heat generated from laptops can significantly elevate the temperature of the scrotum potentially putting sperm count at risk. The small study, which included little more than two dozen men ages 13 to 35, found that the sitting position required to balance a laptop can raise scrotum temperature by as much as 2.1°C
. Heat
from the laptop itself can raise the temperature by another 0.7°C, bringing the potential total increase to 2.8°C. However, further research is needed to determine whether this directly affects sterility in men. [] A common practical solution to this problem is to place the laptop on a table or desk.

Security
Laptops are generally prized targets of theft, and theft of laptops can lead to more serious problems such as identity theft from stolen credit card numbers.[6 Most laptops have a Kensington security slot to chain the computer to a desk with a third party security cable. In addition to this, modern operating systems and software may have disk encryption functionality that renders the data on the laptop's hard drive unreadable without a key, providing the laptop was not turned on while stolen