Most modern internal laptop hard drives use a SATA connection to interface with the computer; however, older drives use the EIDE connection type and external hard drives can use a range of connectors. Laptop hard drives work on the same principles as desktop hard drives, but use a smaller form factor to play on the laptop's portability -- 3.5 inches rather than 2.5 or 1.8 inches. Laptop hard drives have a fraction of a desktop hard drive's profile, often featuring slower performance and less storage for the same cost as desktop drives.
SATA Laptop Connection
SATA laptop hard drives can be identified by the two L-shaped connectors located on the back of the device. The data connector is about half as long as the power connector. SATA is the most commonly supported laptop hard drive connection type and offers substantial performance gains over EIDE. All SATA hard drives use the same connectors, making the laptop versions compatible with desktop computers without requiring an adapter. SATA hard drives usually slide in to the connectors in the laptop hard drive bay. SATA 3.0 hard drives can reach transfer speeds of up to 6Gbps.
EIDE Laptop Connection
Retroactively referred to as PATA, EIDE laptop hard drives use a 44-pin based connection type. EIDE hard drives can be easily differentiated from SATA drives by the substantially different pin connector located on the back of the drive. Laptop and desktop computers use different EIDE connectors; the desktop version separates the power connector. Desktop computers need an adapter to access laptop EIDE hard drives. Additionally, EIDE hard drives may use a pin-adapter to connect to the laptop's motherboard. EIDE hard drives can reach transfer speeds of around 1Gbps.
Hitachi 1.8" Drive Side Connector
Hitachi 1.8-inch hard drives may use a proprietary side connector that's incompatible with standard EIDE and SATA connectors. The Hitachi side connector resembles the EIDE pin-style setup, but appears on the wider side of the drive instead of the back (Reference 3). Hitachi 1.8-inch side connecting drives are specific to Hitachi devices.
External Laptop Hard Drives
From a connection standpoint, desktop hard drives and laptop hard drives are cross-compatible; the problem, though, is fitting a desktop hard drive inside a laptop. External hard drives work around the physical size limitation by connecting to the computer via an external port. External hard drives are found in four main connection type flavors: USB, Firewire, ESATA and Thunderbolt. A particular external hard drive model may come in several variations to accommodate different connection types. USB ports are found on almost every laptop; however, the other connection types are not as frequently supported. SCSI and SAS hard drives are not found inside laptop computers, but the devices can be accessed though an external connection port and adapter.
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