Specifications of an Optical Drive

Various types of optical drives are available in the market. These include CD readers, CD writers, DVD readers, DVD writers, DVD combos, BD readers, BD writers and BD combos.

The specifications of an Optical Drive drives to be considered are:

Supported Media Types: The optical drive must support a major part of available types of discs in the market. Examples are CD-ROM ,

DVD-R ,DVD-ROM ,CD-RW ,CD-R ,DVD-RAM ,DVD-RW ,DVD+R and DVD+RW. Note that CD drives do not support DVD's or BD's and DVD drives do not support BD's. Also, the supported media types are different for a drive's read and write capabilities.

Interface: The interface that an optical drive uses and the port that it will use to connect to the system. The interfaces have transfer speeds of their own. For example, a max. of 167 MBps for IDE, 600 MBps for SATA. But, the current technologies available for optical drives can only provide speeds that are lower than modern systems. So in case, both the ports are available in your system, the interface is not much of a specification.

Buffer Size: The optical drive buffer works in exactly the same manner as the cache of a hard drive It stores a fraction of frequently accessed data that can be accessed extremely fast. It helps the system to access data from the drive even if the processor is being utilized 100% by other processes for a fraction of a second. Usually 1 or 2 or 4 MB.

Read & Write Speeds: All optical drives have different read and write speeds and different read or write speeds for different types of media. For example, DVD drives have a speed of 16x, 20x, 24x (where x is 1.35 MBps) and CD drives have a speed of 32x, 48x, 52x (where x is 150 KBps). An optical drive will always write different types of media at different speeds (For example, a CD at 48x, a DVD at 16x and a re-writable DVD at 4x). 

Specifications of a Hard Disk

Hard Disks have a few performance specifications that a buyer must always know accurately before purchasing the hard disk. Better specs will obviously make the system perform faster. The specifications are:

• Capacity: The amount of data that the disk can store. Usually 100's of GB's or TB's.
• Cache: A small memory chip that stores a fraction of frequently accessed data that can be accessed extremely fast. Usually 8 or 16 or 32 or 64 MB.
• Spin Speed: The speed at which the hard disk platter rotates. Usually, 5400 or 7200 or 10000 rpm.
• Average Seek Time: The average time in which the R/W head can be positioned over the requested track for random read/write requests. Usually, ~8-10 ms.
• Average Latency: The average time for the disk to rotate the platter and position the correct sector under the R/W head. Usually, ~3-5 ms.
• Interface: The interface that the hard disk uses and the port that it will use to connect to the system. The interfaces also have transfer speeds of their own. For example, a max. of 167 MBps for IDE, 600 MBps for SATA.

Hardware caches

The first type of caches, the Hardware caches are usually memory chips that have been embedded within a device. The most common Hardware caches found in a computer system are:

• CPU cache: The L1,L2,L3 caches are used to speed-up data transfer between the processor and the main memory(i.e. RAM). The L1 and L2 caches are built right into the processor chip making them extremely fast. Whereas the newer L3 cache which also has higher capacity than L1 and L2, may be built into the motherboard as well.

• Optical drive cache: A small cache (typically 1-2 MB) is provided in all optical drives, whether CD or DVD or BD. This cache is present so that the disk burner has data available for burning, even if the CPU hits 100% utilization in some other process for a fraction of a second. The cache is also used to store data for fast access when a readable disk is first inserted into the drive.

• Hard-Disk cache: Hard-disks are the fastest permanent storage devices. They can virtually read and write data at the same time. For this purpose, a cache memory is provided in the hard drives that perform in a similar manner like the optical drive caches. The only difference is in their memory size. These may range from 8MB to 64MB.

Usually, the Hard-Disk and the Optical Disk caches are built into the hard-disk controller and the optical disk controller which are present on the hard-drives and the optical drives themselves.