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Chapter 5
Measurement Definition
Other Measurement Definitions
Other Measurement Definitions
Overwrite Measurement
When old data is overwritten with new data, remnants of previous transitions remain. They
are not completely erased. The overwrite measurement measures the overwrite ratio of a
new data signal with respect to the residual signal from the data previously recorded on the
disk.
As the worst case condition occurs when high frequency (HF) data is written over low
frequency (LF) data, these patterns are usually used for this measurement.
The Agilent E5022/E5023 uses an independent test pattern for this type of test. These are
the overwrite HF and overwrite LF data patterns. Agilent E5022/E5023 measures the RMS
signal amplitudes of the original LF signal and the residual LF signal after overwriting it by
an HF data pattern. They are measured by a spectrum analyzer at the LF fundamental
frequency. In general, high frequency pattern is characterized by having more 111.. 11 bits
than 0’s. And low frequency is characterized by having more 0’s than 1’s in a given pattern.
Overwrite is defined as:
Equation 5-27
Overwrite Definition
Since V
residual
is always less than V
original
the quantity will always be a negative value. In
general, a -30 [dB] and smaller overwrite is considered good while that of less than -25
[dB] is will be unacceptable for commercial drive.
OW dB
(
)
20
V
residual
V
original
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