Hardware Reference
In-Depth Information
Access Time
The access time for an optical drive is measured the same way as for PC hard disk drives.
In other words, the access time is the delay between the drive receiving the command to
read and its actual first reading of a bit of data. Access rates quoted by many manufactur-
ers are an average taken by calculating a series of random reads from a disc.
Buffer/Cache
Mostopticaldrivesincludeinternalbuffersorcachesofmemoryinstalled onboard.These
buffers are actual memory chips installed on the drive's circuit board that enable it to
stage or store data in larger segments before sending it to the PC. A typical buffer can
rangefrom2MBupto8MBormore(dependingonthedrive).Generally,fasterrewritable
drives come with more buffer memory to handle the higher transfer rates.
Direct Memory Access and Ultra-DMA
Busmastering PATA controllers use Direct Memory Access (DMA) or Ultra-DMA trans-
fers to improve performance and reduce CPU utilization. Virtually all modern PATA
drives support Ultra-DMA utilization.
Todeterminewhetheryoursystemhasthisfeatureenabled,opentheDeviceManagerand
check the properties sheet for the controller to view its capabilities.
ToenableDMAtransfersifyourmotherboardanddrivessupportit,opentheDeviceMan-
ager and then open the properties sheet for the controller or drive. Click the Settings or
Advanced Settings tab, and make sure DMA is enabled if available. Depending on which
version of Windows you are using, some have the DMA setting in the controller proper-
ties and others have it with the individual drives.
