|Mr. Fixit's PC Upgrade and Repair
When optical drives were invented they were once thought to be a replacement to the HDD, but later proved to be too slow and have
lower densities than magnetic media. Now, optical drives are often used for archiving. Since optical discs and the drives are becoming
inexpensive, they are standard on most new computers. A new computer may come with 1 or both types of drives.
Here I will discuss different aspects such as Interface, drive speeds, writers, buffer under-runs, CPU utilization, Direct Memory access,
MultiRead, Digital Audio Extraction, and Light Scribe.
These drives are also known as writers. They are called burners for a good reason. The laser's temperature can reach 1,292°F (700°C)
in microseconds! They literally burn discs while writing to them. Burners are classified in 3 speeds: Read, Write, and Re-Write. READ, of
coarse, states the maximum speed the drive is capable of reading the disc, WRITE, indicates the maximum speed the drive can write to
the disc, and RE-WRITE is the speed the drive can erase and re-write data on the disc. This feature is always the slowest since the drive
must first erase current data then write new data at the same time. When writing to a blank disc the write speed takes place, however, if
the disc has data already on it then the re-write speed is in place. Many drives state the speed for each function.
The optical pick-up relies on the reflective properties of the disc. The reflective property of a manufactured disc
is around 70%. Recodable and ReWritable discs use a dye that only has a reflective property of 20%. This
created a problem reading dics in standard drives. To solve the problem with low-reflective dyes, additional
circuitry called an Automatic Gain Control (AGC) was incorporated in new drive designs. DVD drives had
another capability problem. The laser used in DVD drives is much more narrow than that of CD Drives,
Parallel AT Attachment (PATA) is also known as Enhanced Integrated Drive Electronics
(EIDE). IDEs have been used since 1986 and can be found in todays computers. They have a
16-bit 40-pin connector to interface the hard disk to the South Bridge or I/O Controller Hub
(ICH). These can transfer up to 100MB of data per second and 133MB of data per second
CD drive speeds and data transfer rates vary from drive to drive. Stand alone CD players spin the disc between 214 rpm to 497 rpm.
This is the basis for which CD Drive speeds are based upon starting at 1x or single speed. Today's CD drives can spin the disc as high
as 27,808 rpm or 56x meaning the drive can spin up to 56 times the speed of a CD player, thus, faster data transfers. A 56x CD drive
could read an 80-minute CD in less than 1.5 minutes. The advertised speed isn't always the actual speed being used because the
number in front of the 'x' doesn't necessary mean that's how fast the disc is spinning, but, rather how fast data is read, here's why. Optical
discs become unstable around 10,000 RPM at which the disc can shatter from centrifugal force. Three technologies that determine an
optical drive's speed are Constant Linear Velocity (CLV), Constant Angular Velocity (CAV), and Zoned CLV (ZCLV).
When an optical drive uses Constant Linear Velocity (CLV), the data flow stays at a constant rate while the disc's rpm changes. When
a disc is being read near the center, the spiral track is more tightly packed causing the need to spin the disc faster. As the spiral track
reaches the end, or the outer edge, the disc has to spin slower to keep the data at the constant rate. This can be seen in CD players. If
you have a CD player that shows your disc as it spins, insert an audio CD and play track 1. Notice how fast the disc is spinning? Now,
play the last track. As the optical pickup moves to the outer edge, notice how the disc slows down? This is CLV in action. Most Optical
drives use CLV up to 12x, which spins the disc up to 5,959 rpm.
Speeds above 12x made it difficult for the motor to spin up or slow down the disc fast enough to keep up with the data rate. Constant
Angular Velocity (CAV) solves that problem by keeping the rpm of the disc at a constant speed while the data flow rate changes. When
a drive uses CAV the drive runs more quiet with less vibration because CAV can read data faster at a lower rpm than CLV. CAV can read
the outer edge faster than the inner edge while CLV can read the inner edge faster than the outer edge. Here's one way to see just how
fast data moves past the optical pick-up in the drive. Let's say the drive is reading the disc at 56x using CAV. Data will pass over the laser
at 162.8 miles per hour! At that speed the optical pick-up can still distinguish between pits/lands as small as 0.9 microns or 35.4 millionths
of an inch (0.000354 inch)!
Some drives use Partial CLV (PCLV) that only switch from CLV to CAV when the rotational limit is reached, but requires additional
hardware. To solve this problem, newer drives use Zoned CLV (ZCLV). With ZCLV, a Disc is divided into several zones and each zone
would have a set CLV speed. A drive using ZCLV would use maximum RPM while reading the inner tracks of the disc and progressively
decrease, in discrete steps, the RPM as the data is read near the outer tracks. A disc burned using a ZCLV drive will show how the disc
was divided into zones. So, the speed of the drive isn't how fast the disc is spinning but rather how fast data can be read from the disc.
These technologies allow data throughput as high as 81MB/s compared to 1.35MB/s for single speed. If you were to lay the spiral track
on the CD flat from end to end, it would be 3.59 miles (5.77 kilometers) in length.
using a 40-pin/80 conductor cable. It depends on the type of host controller installed on the motherboard and the drives capability. The
computer will have a primary IDE (IDE 0) and sometimes a secondary (IDE 1) controller which are labeled on the motherboard. Each
controller can connect 2 devices 1 master and 1 slave. Hard disks connects to the primary while CD/DVD drives connect to the
secondary controller. DO NOT connect a CD/DVD drive on the same controller as the hard disk as this will significantly decrease
performance. The controller will set the speed to the slowest device. In order to have 2 hard disks on the same controller, the primary
drive, or boot drive, must be set as 'master' using the jumpers in the back of the drive next to the IDE connector. The other drive must be
set to 'slave'. You can install up to 2 hard disks and 2 CD/DVD drives with this configuration.
Serial AT Attachment (SATA) was introduced in 2000 and eventually replaced IDE by 2007, transferring up to
600MB of data per second compared to IDEs 133MB/s. SATAs use differential non-return to zero signaling, instead of
wire voltage is +0.25V and the paired wire is -0.25V. This technique reduces there are no jumpers to set. Unlike IDE
drives, SATA drives can be accessed simultaneously giving them a big advantage in performance. You could only
access 1 drive on a host controller at a time with IDE drives. SATA became standard in 2003.
The DVD is an improved version of the CD because it can store up to 11.5 times the data than the CD, even though they are the exact
same size. This is accomplished by using a more narrow laser wave length allowing the optical pickup to distinguish differences between
pits/lands as small as 15.75 millionths of an inch (0.0001575 inches) increasing storage capacity up to 8.5GB on a single disc. DVD
players spins the DVD between 570 rpm to 1,515 rpm. This sets the basis for DVD drive speeds starting at 1x or single speed. DVD
drives can spin the disc as fast as 50x or 75,743 rpm. This also means that DVD drives can read CDs at an increased speed. For
example, a DVD drive spinning at 16x can read a CD at the same speed as a 43x CD drive. Big difference... Many DVD drives list both
speeds for DVD and speeds for CD. DVD drives also use CLV, CAV, and ZCLV the same way as CD drives. The faster drives are mainly
for reading and writing data and not video, however, while watching a video from a dual-layer disc you may not notice the drive changing
from one layer to the other. If the spiral track was unwrapped and laid flat, it would be 7.35 miles in length.
Some things that determine the CD/DVD drive's speed are Access Times, vibrations, and the CD/DVD's condition. No disc is perfect. Disc
vibrations while it spins become worse as it spins faster, which forces the drive to slow down for more accurate disc reading and writing.
Some vibrations are due to some type of label that was added to the disc, throwing it off balance. Some of the faster CD/DVD drives are
equipped with auto-balancing or vibration-control means to solve the problem. Access Times refer to the amount of time it takes the drive
to locate and read the file on the disc. Optical drives are much slower than hard drives with access times ranging from 400ms to 85ms or
less. This is due to the fact that hard drives have multiple heads reading the disc while optical drives only have one optical pick-up
reading the disc. The Disc's condition is another factor in drive speeds (scratches, dust, finger prints, etc.) that affect the accuracy of the
This isn't talked about much. CPU Utilization refers to the amount of CPU resources required by the hardware or software for processing data. The less the
hardware/software depend on the CPU, the more the CPU can attend more important tasks. The drive speed, buffer size, and interface type play a big role in
the CPU utilization. The faster the drive and the larger the buffer memory, the less CPU processing required. Drives with a SATA interface uses less CPU
resources than IDE drives, and drives using Ultra Direct Memory Access (UDMA) modes also requires less CPU interaction.
Direct Memory Access / Ultra Direct Memory Access:
DMA / UDMA allows the drive to access the system memory without having to use the CPU. This reduces CPU usage to 10% or lower, therefore increasing
the drive's efficiency and speed.
Digital Audio Extraction:
Earlier versions of CD drives used 2 separate cables; the IDE cable and the CD audio cable. When these drives played an Audio CD,
the drive would convert the digital information on the disc into analog then send it to the sound card via the audio cable. If you wanted to
record the CD, you had to use a recording software that would revert the audio back to digital to save on the computer which could result
in the loss of sound quality. Newer CD drives can now perform Digital Audio Extraction. This process, a.k.a. ripping, reads the Digital
Audio directly from the disc without having to convert to analog and back to digital allowing the audio file to be exactly what was on the
disc (within the ability of the error correction standards of the drive).
Access Time refers to the amount of time, in milliseconds, it takes from the moment the drive receives the command to the drive reading
the first bit of data. Many CD/DVD drives today have an average access time of 90ms or less. The actual access time will depend where
the data is located on the disc. For example, data that is closer to the center of the disc will have a faster access time than if it was
located closer to the outer edge. It will also depend if the drive is using the CLV or CAV method to retrieve the data.
making Recordable CDs harder to read in DVD drives. Today, DVD drives may contain a dual-laser optical pickup that would allow a
DVD drive to read CDs. This became known as the MultiRead Standard. To identify a Drive's capabilty to recordable medias look for the
MultiRead logo on the drive. All CD medias can be read in MultiRead and MultiRead2 drives whereas DVD medias can only be read in
MultiRead2 drives. MultiRead2 DVD drives are more expensive since they have a dual laser pickup. There is another standard called
MultiPlay for standalone CD and DVD players. These devices can read recordable discs even if they were burned using packet writing.
All drives have buffer memory built in to the drive ranging from 2MB to 16MB that allows improved performance. In earlier burner drives, users sometimes
experienced the Buffer Under-run Error. The error was caused by the failure of the computer to keep up with the drive during a burn session and basically
made the disc unusable. With Buffer Under-run Protection, the drive could actually stop in the event the buffer is empty, wait for the computer to send more
data then resume writing where it left off.