Data processing: database and file management or data structures – Database design – Data structure types
Reexamination Certificate
1998-04-30
2001-02-27
Amsbury, Wayne (Department: 2771)
Data processing: database and file management or data structures
Database design
Data structure types
C370S394000
Reexamination Certificate
active
06195663
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a data server and, more particularly, to a data server having a packet token generator that facilitates the high speed transfer of data over an SCSI (small computer system interface) bus.
BACKGROUND OF THE INVENTION
A hard disk based data server offers high speed random data accessing capability which is useful, for example, in digital video applications such as interactive video processing, non-linear video editing, test video stream generation, and the like. The data servers that have been developed in the past for these applications primarily involve the use of the SCSI protocol because the SCSI protocol has many advantages including compatibility, expandability, and exchangeability. However, these data servers have been either low speed, low cost data servers, or high speed, high cost data servers.
A typical data server
10
implementing the SCSI protocol is illustrated in FIG.
1
. The data server
10
includes an SCSI disk
12
for storing data which must be accessed and processed by an application
14
. The application
14
accesses the data stored on the SCSI disk
12
through a host computer
16
and an SCSI bus adapter
18
. The host computer
16
communicates with the SCSI bus adapter
18
over a host bus
20
, and the SCSI bus adapter
18
is connected to the SCSI disk
12
by way of an SCSI bus
22
.
One typical requirement demanded for the design of the data server
10
is that the host computer
16
, the SCSI bus adapter
18
, and the host bus
20
be able to handle the data flow at substantially the same data rates of the SCSI disk
12
and the application
14
. While this requirement is technically feasible when the data rate is high, satisfying this requirement at high data rates results in the data server
10
being complicated and costly.
Moreover, unless the data server
10
is highly complicated, the data server
10
is not flexible, simple, or fast, because only the SCSI bus adapter
18
communicates with the SCSI disk
12
. For example, as the application
14
processes data stored on the SCSI disk
12
, it repeatedly starts and stops data flow from the SCSI disk
12
because the SCSI disk
12
delivers data at a rate which is faster than the processing rate of the application
14
. However, all start and stop instructions from the application
14
must be passed to the SCSI disk
12
through the host computer
16
and the SCSI bus adapter
18
, which tends to slow down data transfer.
Furthermore, the application
14
may issue data requests at a frequency which is higher than the required data transfer rate of the data file on the SCSI disk
12
. The data server
10
must be able to compensate for the difference between the frequency of the data requests from the application
14
and the data transfer rate of the data file on the SCSI disk
12
.
In order to develop a low cost and high performance data server, the present invention takes the approach of directly controlling the data flow of the SCSI disk by the application hardware. However, if the application hardware is to control the data flow, care must be exercised so that the data rate is controlled in a simple way and with the required jitter performance and so that the data rate is controlled at any given data rate in a wide range.
Accordingly, the present invention is directed to a packet token generator which achieves these performance requirements. The data server based on the present invention is fast, flexible and/or low cost compared to prior art data servers, particularly to prior art video servers.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a data server includes a token generator. The token generator generates tokens. The data server is arranged to send data to an output if a token is generated so as to be substantially coincidental with a data request, and the data server is arranged to send null data to the output if a token is not generated so as to be substantially coincidental with a data request.
In accordance with another aspect of the present invention, a data server comprises a memory, a data bus connected to the memory, and a bus controller connected to the bus. The bus controller includes a token generator that generates tokens. The bus controller is arranged to transfer data from the memory to an output of the data server if a data request and a token are substantially coincident, and the bus controller is arranged to transmit null data to the output of the data server if a data request and a token are not substantially coincident.
In accordance with yet another aspect of the present invention, a data server comprises an SCSI storage disk, an SCSI bus connected to the SCSI storage disk, an SCSI bus adapter connected to the SCSI bus, a host computer arranged to control the SCSI bus adapter, and an application connected directly to the SCSI bus. The application is arranged to receive the data transferred by the SCSI bus and to control these transfer of the data from the storage disk. The application includes a token generator that generates tokens. The application is arranged to transfer data from the SCSI storage disk to an output of the data server if a data request and a token are substantially coincident, and the application is arranged to transmit null data to the output of the data server if a data request and a token are not substantially coincident.
REFERENCES:
patent: 4792926 (1988-12-01), Roberts
patent: 5548790 (1996-08-01), Mayer
patent: 5561791 (1996-10-01), Mendelson et al.
patent: 5566169 (1996-10-01), Rangan et al.
patent: 5668811 (1997-09-01), Worsley et al.
patent: 5742599 (1998-04-01), Lin et al.
patent: 5878041 (1999-03-01), Yamanaka et al.
Amsbury Wayne
Zenith Electronics Corporation
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