48
DVX
Instruction
Manual
APPENDIX
LOGICAL BLOCKS AND SECTORS
CD Discs
Data CDs are arranged in sectors, so that the data can be randomly accessed. These sectors are always of a fixed size,
but the amount of user data may vary. Also, each sector may contain additional parity bytes for error correction,
depending on the mode.
Audio discs have no sectors; the data is a continuous stream of music. However, they do have time code that can be
correlated to sectors. The size of a subcode frame is the same as the size of a sector on a data disc. Therefore, it is
possible to convert between Atime and Sector number.
Physical sector numbers start at the beginning of the disc, and continue to the end. However, the first 150 sectors of a
data disc are used for pre-gap, and contain no information. Therefore, the data area begins at physical sector 150, and
is called Logical Block 1. Logical Blocks (abbreviated LBA for Logical Block Address) are the same thing as physical
sectors; the only difference is that they are numbered beginning at physical sector 150. Whenever we refer to a data
disc sector, we mean physical sector unless we say logical block or LBA.
DVX software uses both physical sectors and logical block addresses. When entering START and STOP points, use
physical sectors. When viewing disc data, use logical block addresses.
DVD Discs
All DVD discs are addressed using
L
ogical
B
lock
A
ddresses. DVD locations are never entered in physical sector
numbers or Minutes:Seconds:Frames.
How QuickScan
TM
works
QuickScan
TM
is an exclusive feature of DVX that speeds up testing by 3½ times for CDs and 8 to 10 times for DVDs.
This allows you to test an 80 minute CD in as little as 48 seconds, or a DVD5 in 38 seconds. The
shows test times for various types of discs with and without QuickScan
TM
.
QuickScan works by testing only samples of the disc. If the samples are very close together physically on the disc, no
significant information is lost. Serious errors are caused by physical defects that prevent the drive from reading the
data on the disc. Due to the powerful error correction on CD and DVD discs, a physical defect has to be about 100µm
in diameter to cause serious errors. Therefore, if we sample the disc every 50µm, there is no chance of missing a
significant defect. Samples are designed so that they always cover at least one complete revolution of the disc (and
usually much more). Then the pickup jumps ahead 50µm to the next sample. Any defect in the skipped section would
have to be no more than 50µm in size, and therefore would not generate any serious error. In practice, defects are
usually much larger than this, and may even include the entire disc.
QuickScan works at all test speeds. So 2X becomes 7X, 4X becomes 14X, etc. When QuickScan is enabled, the status
bar shows the current speed as “48X MAX QS” for instance instead of “48X MAX” so you can know when QuickScan
is enabled. The Summary Report also shows whether QuickScan was used for the test.
