Which Hard Drive Should I buy?

The best performance and value right now is the Seagate Barracuda line. With a rotation speed of 7200 rpm and an average seek time of 8.5 ms.

Determining needed performance level
The performance level necessary depends more on how the system is being used than anything else. System usage generally falls into one of three categories:

Desktop PCs
The average home or small business desktop user rarely puts enough demands on the system to require high-level performance. While many users may desire high performance ratings, such features will rarely provide a noticeable difference in this environment. We suggest ATA, Performance ATA, or SCSI for this usage category.

Midrange Servers and Workstations
Midrange servers and workstations are designed for business environments with light to medium work loads, meaning approximately 10-50 people simultaneously accessing the server or workstation on a random basis during normal business hours. We suggest Performance SCSI for this usage category.

High Performance Servers and Workstations
High-performance servers and workstations are designed for mission critical, heavy-use file servers, meaning more than 50 people simultaneously accessing on a 24-hours-a-day basis, and high demand workstations such as those used for Audio/Video production. We suggest High-End SCSI for this usage category.

Disc drive features directly related to performance

While most disc drive specifications relate to drive performance in some way, the following short list contains those features that can have a noticeable impact on system performance.

Data transfer rate describes how fast data can actually be read or written to the physical platters inside the drive – commonly referred to as internal transfer rate.

External transfer rate describes the amount of data that can be transferred from the drive's host controller to the interface controller - commonly referred to as burst transfer rate.

Cache memory is the physical computer memory chip on a disc drive where data is stored temporarily on the drive until the host bus adapter requests the data. Cache acts as a buffer between the data on the disc platters and the host bus adapter.

Access time describes how fast the drive can locate data on the disc platters and is especially important in a file server or similar random-access environment. Rotational speed indicates the maximum speed at which the platters can spin to place a particular data storage point under the read/write heads.

Rotational speed as a measurement is determined by the maximum number of revolutions the platters can make in one minute (RPM). Generally, a higher RPM produces a better internal data transfer rate, a lower access time, and better overall drive performance.