• Determining needed performance level
• Disc drive features directly related to performance

Determining needed performance level

The performance level necessary depends predominantly on how the system is being used. 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. Drives using ATA or SATA interfaces are the best fit for this usage category.
  
  
• Notebook Computers
  Most notebook computers use smaller 2.5-inch drives which have a specialised ATA interface for notebook use. Newer laptops have started to use Serial ATA (SATA). These are specialised drives.
  
  
• High-Performance Servers and Workstations
  High-performance servers and workstations are designed as mission-critical, heavy-use file servers, accessed by more than 10 simultaneous users on a 24-hour-a-day basis, and high-demand workstations such as those used for Audio/Video production. We suggest High-End SCSI or Fibre Channel drives 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.

• Internal Data transfer rate describes how fast data can actually be read or written to the physical platters inside the drive. The figure below shows some example internal transfer rates:

  ATA	SCSI	High-End SCSI
  Barracuda 7200.10	Cheetah 10K.7	Cheetah 15K.4
  up to 1030 Mbits/sec	up to 944 Mbits/sec	up to 1142 Mbits/sec

  
  
• External Data 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. This is most critical in multiple-drive installations where several drives may have to share the interface bandwidth.
  
  

  ATA/Serial ATA	SCSI	High-End SCSI
  Barracuda 7200.10	Cheetah 10K.7	Cheetah 15K.4
  300 Mbytes/sec	320 Mbytes/sec	320 Mbytes/sec

  
  
• Cache memory is the memory on a disc drive where data is stored temporarily until requested by the host bus adapter. Cache acts as a buffer between the data on the disc platters and the host bus adapter.
  
  

  ATA	SCSI	High-End SCSI
  Barracuda 7200.10	Cheetah 10K.7	Cheetah 15K.4
  8-16 Mbytes	8 Mbytes	8 Mbytes

  
  
• 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.
  
  

  ATA	SCSI	High-End SCSI
  Barracuda 7200.10	Cheetah 10K.7	Cheetah 15K.4
  11 milliseconds	4.7 - 5.3 milliseconds	3.6 - 4.0 milliseconds

  
  
• 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 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.
  
  

  ATA	SCSI	High-End SCSI
  Barracuda 7200.10	Cheetah 10K.7	Cheetah 15K.4
  7,200 RPM	10,000 RPM	15,000 RPM

  
  

The examples above are from drives within a given family. For the specifications of a particular product please refer to the product manual for that model.