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1991-09-27
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Stac Electronics
5993 Avenida Encinas
Carlsbad, CA 92008
(800) 225-1128 [ordering information number]
Reproduction of Press Release dated 09/16/91
Announcing Stacker version 2.0
STACKER PRODUCT FAMILY
Technology ------------------------------------------------------
* Operating Systems DOS 3.x and above, Compaq DOS
3.1, DR DOS
* Operating Environments Microsoft Windows 3.0
* Utilities Norton Utilities, PC Tools
* Disk Caching Programs PC Tools, Super PC-Kwik
* Disks and Drives Floppy, Bernoulli, RAM, IDE, MFM,
SCSI, RLL
Performance -----------------------------------------------------
* Compression Ratio 2:1 average; up to 18:1 on some files
* Speed Up to 5 megabytes a second
Installation ----------------------------------------------------
* Includes Symantec/Norton Speed Disk
* Detects Coprocessor Board Being Installed
* Performs System Recognition and Diagnostics
* Program Loadable Into High Memory
* Improved User Interface
* No Reformatting
* No DMA Channels or Interrupts to Set
* No Jumpers or Switches on Board to Set
Utilities -------------------------------------------------------
* Defragmenter
* Grow and Shrink Stacker Drives
Selection -------------------------------------------------------
* STACKER 2.0
Software Only
30K-byte program
Suggested retail: $149
Ideal for laptop, notebook and portable computers
* STACKER XT/8
8-bit coprocessor card
Stacker 2.0 included -- 21K-byte program
Suggested retail: $199
Designed for IBM PCs, XTs and compatibles
* STACKER AT/16
16-bit coprocessor card
Stacker 2.0 included -- 21K-byte program
Suggested retail: $249
Designed for all 80286-, 80386-, and 80486- based PCs
and compatibles
* STACKER MC/16
16-bit coprocessor card
Stacker 2.0 included -- 21K-byte program
Suggested retail: $299
Designed for Microchannel-based IBM PS/2s and compatible
STACKER TECHNOLOGY
What is Stacker -------------------------------------------------
The Stacker[TM] MS-DOS device driver implements a virtual disk
with twice the capacity of the physical disk. It works by
reducing the number of sectors required to hold an MS-DOS
cluster.
How Stacker Works -----------------------------------------------
As the Stacker device driver is called upon to write a cluster
of data, it calls upon the Stac compression technology in
either hardware or software to compress the data in the
cluster. Once compressed, the data is allocated to the
minimum integral number of sectors necessary to contain the
compressed cluster.
Stacker uses either a 4K or 8K byte cluster. Normally, MS-DOS
would require eight 512-byte sectors to store a 4K cluster.
By compressing the data by a factor of 2, on the average,
Stacker uses only half the number of sectors to store the same
amount of data. In the case of a 4K cluster, 2:1 compression
yields four sectors per cluster rather than eight. The result
is a doubling of capacity on a compressed volume.
The Stacker Algorithm Consists of Two Elements ------------------
* An MS-DOS device driver that compresses all data before it
is written to a storage device and decompresses all data
as it is read.
* Stacker LZS[TM], a high-speed lossless compression
algorithm, is implemented in a coprocessor chip or in
software.
The Stacker LZS algorithm looks for repeated string in a
window. The window within which string matches can be found
always contains the most recently processed 2,048 bytes. The
technique employed gets its name, sliding window, because the
window slides forward through a file as bytes are processed.
Useful Definitions ----------------------------------------------
Algorithm: A predetermined set of instructions for solving a
specific problem in a limited number of steps.
Cluster: Unit of storage allocation used by MS-DOS, usually
consisting of four or more 512-byte sectors.
Lossless: No information is lost or altered in the
compression process.
LZ: Lempel Ziv is a lossless adaptive compression
algorithm first published in 1977. LZ looks for
matches in a file it is compressing or
decompressing and replaces occurrences of
repeated strings with shorter tokens. The
tokens are used during decompression to
reconstruct the original strings.
Real Time: Compressing all data on the way to the disk as it
is written, and decompressing the data as it is
read back from the disk as quickly as the host
computer can move it.
Sector: A unit of allocations used by Winchester disk
drives, usually 512 bytes.
Sliding
Window: A 2,048-byte sliding segment of a file where the
Stacker algorithm looks for repeated strings.
Strings: A sequence of bytes.