Preamplifier And Write Driver; Firmware Features; Disk Caching - Quantum FIREBALL PLUS AS 10.2 Product Manual

5.2.3 5.2.3 5.2.3 5.2.3

PreAmplifier and Write Driver

PreAmplifier and Write Driver PreAmplifier and Write Driver PreAmplifier and Write Driver
The PreAmplifier and Write Driver provides write driver and read pre-amplifier
functions, and R/W head selection. The write driver receives precompensated write
data from the PreCompensator module in the Read/Write ASIC. The write driver
then sends this data to the heads in the form of a corresponding alternating current.
The read pre-amplifier amplifies the low-amplitude voltages generated by the R/W
heads, and transmits them to the VGA module in the Read/Write ASIC. Head select
is determined by the controller. The preamp also contains internal compensation
for thermal asperity induced amplitude variation.
5.3 5.3 5.3 5.3

FIRMWARE FEATURES

FIRMWARE FEATURES FIRMWARE FEATURES FIRMWARE FEATURES
This section describes the following firmware features:

• Disk caching

• Head and cylinder skewing
• Error detection and correction
• Defect management
5.3.1 5.3.1 5.3.1 5.3.1 Disk Caching Disk Caching Disk Caching Disk Caching
The Quantum Fireball Plus AS AT hard disk drives incorporate DisCache, a
1.9 MB disk cache, to enhance drive performance. This integrated feature is
user-programmable and can significantly improve system throughput. Read
and write caching can be enabled or disabled by using the Set Configuration
command.
5.3.1.1 5.3.1.1 Adaptive Caching Adaptive Caching
5.3.1.1 5.3.1.1 Adaptive Caching Adaptive Caching
The cache buffer for the Quantum Fireball Plus AS drives features adaptive
segmentation for more efficient use of the buffer's RAM. With this feature, the
buffer space used for read and write operations is dynamically allocated. The cache
can be flexibly divided into several segments under program control. Each segment
contains one cache entry.
A cache entry consists of the requested read data plus its corresponding prefetch
data. Adaptive segmentation allows the drive to make optimum use of the buffer.
The amount of stored data can be increased.
5.3.1.2 5.3.1.2 5.3.1.2 5.3.1.2 Read Cache Read Cache Read Cache Read Cache
DisCache anticipates host-system requests for data and stores that data for faster
access. When the host requests a particular segment of data, the caching feature
uses a prefetch strategy to "look ahead", and automatically store the subsequent
data from the disk into high-speed RAM. If the host requests this subsequent data,
the RAM is accessed rather than the disk.
Since typically 50 percent or more of all disk requests are sequential, there is a high
probability that subsequent data requested will be in the cache. This cached data
can be retrieved in microseconds rather than milliseconds. As a result, DisCache
can provide substantial time savings during at least half of all disk requests. In these
instances, DisCache could save most of the disk transaction time by eliminating the
seek and rotational latency delays that dominate the typical disk transaction. For
example, in a 1K data transfer, these delays make up to 90 percent of the elapsed
time.
Quantum Fireball Plus AS 10.2/20.5/30.0/40.0/60.0 GB AT
Basic Principles of Operation
5-10