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Description  |
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BACKGROUND
1. The Field of the Invention
This invention relates to systems and methods for transferring digital data
within computer systems. More particularly, the present invention pertains
to a high speed communication path that allows one or more remote
computers to share the resources of a high speed host computer, thereby
increasing the speed of operation of the remote computers.
2. The Background Art
Modern digital computers have become essential to business, science,
industry, and military operations throughout the industrial world. In
particular, the widespread availability of microcomputers, also often
referred to as "personal computers", has made digital computers accessible
to more people than ever before.
The affordability and widespread use of the microcomputer has caused a
myriad of different microcomputer application programs to become available
directed to those tasks that the microcomputer is best adapted. Many such
applications, however, require the additional power of a mini or mainframe
computer system unavailable in a microcomputer. Thus, many facilities are
equipped with both a powerful mainframe or minicomputer, as well as a
plurality of remote microcomputers located on the site.
Disadvantageously, the operating systems, architectures, and standards that
have been developed for the microcomputer have differed from those
developed for larger computer systems In view of the desire to retain
efficient operations, these differences have made the interfacing of the
different types of computers quite difficult.
Moreover, the internal and peripheral devices used with larger computers
are often faster than the corresponding devices associated with each of
the microcomputers. For example, while it is not generally economical to
provide each microcomputer with a high capacity, fast-access magnetic hard
disk drive memory device, it is effective to provide such a magnetic hard
disk drive in connection with a mini or mainframe computer. Also, it is
common for a high speed, high quality printer to be associated with a mini
or mainframe computer, while not with a microcomputer.
Large computer systems often have excess space on their disk drive memory.
Also, the printers associated with larger computers often sit idle much of
the time. For these reasons, and because it is generally desirable to
allow remote microcomputers to communicate with larger host computers,
there has been a yet unfulfilled need for an effective communication link
between a plurality of remote microcomputers and a larger host computer,
whereby the remote computers could utilize directly the resources of the
host computer.
Unfortunately, previously available computer systems do not provide for
communication between a remote and a host computer in a manner that
permits the remote computer to efficiently use the resources of the host
computer. For example, data transmission systems such as local area
networks and terminal communication systems, utilize serial data
communication techniques that transmit data bits between computers one at
a time over cables. This severely limits the speed of communication making
impractical the transmission of data on a "clock cycle" basis, which is
necessary for memory accesses by a microprocessor. The arbitration and
managing functions exercised by local area networks slow communications
even further. Thus, it has long been a need in the art that a remote
computer and a host computer be able to communicate fast enough to share
resources efficiently.
In view of the foregoing, it would be advantageous to develop a system and
method for allowing a remote computer to share the resources of a host
computer by providing high speed communication between the two. It would
be a further advance if such a system were to allow a remote computer to
access the disk drive of a host computer as a virtual disk drive. It would
further benefit the users of smaller computers to provide a communication
system for allowing a plurality of remote computers to off-load printing
tasks to a host computer and to allow a remote computer to organize files
into virtual disk partitions in a host computer disk drive. A data
communication system for allowing one or more networks of remote computers
to share the resources of a host computer, such as sharing of printers and
file transfer functions, would be even a further step forward.
OBJECTS AND BRIEF SUMMARY OF THE INVENTION
In view of the foregoing, it is a primary object of the present invention
to allow one or more remote computers to share and access the resources of
a host computer. Such resources could include, for example, a plurality of
operating systems available on the host computer.
Yet another object of the present invention is to increase the overall
throughput of one or more remote computers.
An additional object of the present invention involves allowing one or more
remote computers to share a peripheral device, such as a printer, that is
associated with a host computer.
It is a further object of the present invention to decrease disk access
times for a plurality of remote computers.
The present invention also has an objective of providing a high-speed
communication path between a host computer and a remote computer.
It is yet another object of the present invention to enable one or more
networks of remote computers to share the resources of a single host
computer.
Still another object of the present invention is to allow one or more
remote computers to act independently of a host computer, or to act as
virtual terminals for the host computer.
These and other objects of the present invention will be further
appreciated by an examination of this disclosure and by practicing the
invention.
The present invention provides a high-speed digital communication path
between a host computer and at least one remote computer by establishing a
communication path directly between the internal bus of a host computer
and the internal bus of a remote computer. The system of the present
invention may be described as an interprocessor communication system,
since the communication link established is essentially between the
central processor of a host computer and the central processor of a remote
computer.
In the embodiment of the present invention disclosed herein a host
interface is installed in the host computer and a remote interface is
installed in each remote computer of the system. The host interface allows
digital data and control signals on the bus of the host computer to be
transferred between that host bus to one of several host ports located at
the host interface. Similarly, the remote interface allows digital data
and control signals to be transferred between the bus of each remote
computer and a corresponding remote port located on the remote interface
at that remote computer.
A cable interconnects one of the host ports to each remote port. The
interconnecting cable includes a sufficient number of conductors as to
convey control signals and transmit data in a parallel mode on individual
pairs of conductors. The bus of the remote computer is effectively
rendered an extension of the host bus through the host interface, the
interconnecting cable, and the remote interface.
A multiplexing means is provided in the host interface to sequentially
multiplex either an address or digital data that is to be presented at the
host port and thereafter, by way of the interconnecting cable, to the
remote port. Control means in the form of control circuits are provided on
both the remote interface and the host interface.
An address select/decode circuit in conjunction with the control means of
the host interface causes one of several host ports to be selected from an
address presented on the bus of the host computer. Thus, the most
significant bits of an address presented on the bus of the host computer
serves to select which host port is to be accessed. The remaining bits of
an address presented on the bus of the host computer are used to select a
location in a memory means or random access memory, which in the preferred
embodiments is located on the remote interface. In this manner, the host
computer is able to address the remote computer as if it were any other
logical device in association with the host computer.
In the preferred embodiment of the invention disclosed herein, the host
control circuit also regulates the operation of a byte-swapping means, or
byte-swapping data buffer, which corrects the ordering of data bytes to
overcome differences between the byte ordering schemes of the remote and
host computers.
As disclosed herein, the remote computer is an IBM model PC/AT, an IBM
model PC/XT computer, or an equivalent. A remote interface is provided at
each remote computer which includes one remote port that is connected to
the interconnecting cable. The remote interface includes a random access
memory which functions as a temporary storage location for digital data
received from the host computer. Digital data destined to the host
computer from the remote computer is also stored temporarily in the random
access memory. Such digital data is transmitted to the host computer by
way of the remote port, the interconnecting cable, and the host interface.
A control circuit included in the remote interface regulates the transfer
of digital data between the random access memory and the remote port and
bus of the remote computer.
When digital data is being both received by and transmitted from the remote
computer, accesses to the random access memory by the host and remote
computers is interleaved. The structure and speed of operation of the
interfaces produce virtually no delay in the system. The operation of both
the host interface and the remote interface is thus transparent, not only
to a user, but to the remote and host computers.
The structure of the remote interface, the host interface, and the cable
interconnecting the two enables the remote computer to efficiently share
the resources of the host computer and to carry out functions which it
otherwise could not. With the present invention supplemented by suitable
software, a remote computer can access the memory devices of a host
computer and also share the use of peripheral devices, such as printers.
Moreover, the present invention allows for efficient file transfers
between different operating systems and establishes the remote computer as
a very fast terminal for the host computer.
BRIEF DESCRIPTION OF THE DRAWINGS
In the description which follows, and in the accompanying drawings, some of
the figures have been divided into two or more parts in order to increase
their clarity. Where a figure has been divided into two or more parts, a
number designation has been added as a suffix to the figure number for
each part into which the figure has been divided. For example, in the
detailed schematic diagram provided in FIG. 5, the figure has been divided
into two parts designated as "FIG. 5-1" and "FIG. 5-2." In the case of
figures which have been divided into two or more parts, the complete
figure may be reassembled by placing the first part of the figure in an
upper left position, the second part in an upper right position, and the
third part in a lower right position. Boxed letters at the margins of a
figure that has been divided into parts indicate electrical
interconnections between the parts of that figure.
FIG. 1 is a schematic representation of one arrangement of a host computer
and a plurality of remote computers interconnected by a preferred
embodiment of the system of the present invention.
FIG. 2 is a schematic representation of one arrangement of a host computer
and a local area network including a plurality of remote computers, one of
which is interconnected to the host computer by the system of the present
invention shown in FIG. 1.
FIG. 3 is a schematic representation of one arrangement of a host computer
and a local area network including a plurality of remote computers, two of
which are interconnected to the host computer by the system of the present
invention shown in FIG. 1.
FIG. 4 is a block diagram representing the structure of the host interface
of the system of the present invention shown in FIG. 1.
FIGS. 5-1 and 5-2 provide a detailed schematic diagram of the control
circuit of the host interface represented in FIG. 4.
FIG. 6 is a block diagram showing the structure of the byte swapping data
buffer of the system of the present invention represented in FIG. 4.
FIG. 7 is a block diagram showing the structure of the host ports of the
system of the present invention represented in FIG. 4.
FIG. 8 is a block diagram representing the structure of the remote
interface of the system of the present invention shown in FIG. 1.
FIGS. 9-1, 9-2, and 9-3 provide a detailed schematic diagram of the control
circuit of the remote interface represented in FIG. 8.
FIG. 10 is a block diagram showing the structure of the remote port of the
system of the present invention represented in FIG. 8.
FIG. 11 is a state machine diagram for the state machines implemented in
the components shown in FIGS. 9-1, 9-2, and 9-3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In the following description, like structures will be identified by like
reference characters. It is to be understood that the structures described
herein merely represent a presently preferred embodiment of the invention.
Thus, the present invention may be implemented in many ways and
incorporated into many computer systems, other than those described
herein.
General Overview
As indicated earlier, the need has long existed in the computer industry
that one or more remote computer systems be able to share the resources of
a host computer, such as magnetic disk drives and printers. High-speed,
high-quality magnetic disk drives and printers are mechanical devices that
are particularly expensive to acquire and maintain. Thus, it is important
that a computer system make maximum use of these devices. Allowing a
plurality of remote computers to share these resources is much more cost
effective than providing each remote computer with its own magnetic disk
drive and printer of the same capacity as that provided to the host
computer.
The sharing of resources, such as disk drives and printers, between a host
and remote computer requires, however, that a very fast communication path
be established between the two. The present invention provides such a
high-speed communication path in the form of an interface provided at both
the host computer and each of the remote computers for enabling a
high-speed, processor-to-processor communication path. This allows many
other functions to be carried out which would otherwise not be possible.
FIG. 1 illustrates one possible application of the present invention. A
host computer 10 is shown as being provided with a host interface 12 that
is preferably fabricated on a single circuit board that is selectively
insertable and removable from host computer 10.
In the illustrated embodiment, host interface 12 is provided with six (6)
host ports 14A-14F. In the application represented in FIG. 1, each of host
ports 14A-14F is connected individually by a corresponding one of
interconnecting cables 16A-16F to individual remote interfaces 20A-20F,
respectively. Each of remote interfaces 20A-20F is preferably fabricated
on a distinct circuit board to allow for its easy installation into host
computer 10. Remote interfaces 20C-20F are designed to be readily
installed in a number of different remote computers, two of which are
shown in FIG. 1 by way of illustration as remote computers 22A and 22B.
In the presently preferred embodiment of the invention, remote computers
22A and 22B are IBM model PC/AT or model PC/XT computers, their
equivalent, or another work station which incorporates the expansion bus
of the IBM model PC/AT or model PC/XT computers. While the embodiment
described herein is particularly adapted for use with such remote
computers, the present invention may be implemented in many different
forms and used with many different host and remote computer systems.
The embodiment of the present invention represented in FIG. 1 affords many
advantageous capabilities to a user and many different benefits. Among
these are (1) a virtual disk function, (2) a virtual terminal function,
(3) a file transfer function, and (4) a print spooling function. Each will
be explained below.
Each remote computer 22A-22B is given access to the disk drive of the host
computer 10. This is the virtual disk function carried out by the system
of the present invention. Using appropriate software, the system shown in
FIG. 1 makes it appear to the processor of remote computers 22A-22B that
the disk drive of host computer 10 is internal to each respective remote
computer 22A-22B. Thus, the system of the present invention is transparent
to the central processing units of the host computer 10 and to remote
computers 22A-22B.
In the embodiment of the inventive system shown in FIG. 1, remote computers
22A-22B utilize the MS-DOS operating system. In such an operating system
each virtual disk drive of host computer 10 simply appears to remote
computers 22A-22B as a different internal designated disk drive, such as
drive C, drive D, and so forth. The virtual disk drive function provided
by the present invention may be organized and partitioned as any other
MS-DOS disk drive for easy access and information sharing.
The host disk drive can be a very large, fast and efficient device. For
example, a host disk drive may use a disk cache scheme. In such a disk
cache scheme, often accessed data is moved from disk into a dedicated
random access memory where it can be accessed in much less time than if a
disk access were required. Furthermore, multiple disk drives may be
included in the host computer.
The communication path between the remote computers and the host computer
is also fast. Therefore, the use of the virtual disk drive function allows
a remote computer to effect disk drive accesses faster than might
otherwise be possible using a disk drive internal to the remote computer.
This results in responsive remote computer operation.
The virtual terminal function of the inventive system allows the remote
computers 22A-22B to be connected to the central processing unit of host
computer 10 and act as terminals thereof. The extremely fast communication
path between host computer 10 and remote computers 22A-22B provides screen
updates that are effectively instantaneous.
A file transfer function may also be efficiently carried out using the
present invention. The file transfer function allows a user to easily move
files between different operating system environments. For example, in the
presently preferred embodiment, file transfers may be effected between the
UNIX, PICK, and MS-DOS operating system environments.
With the high-speed communication pathway provided by the present invention
between each remote computer 22A-22B and host computer 10, the sharing of
a printer or "print spooling" may also be accomplished. This feature
permits the sharing of expensive printing devices, such as laser printers.
The spooling for each printer occurs on a first-come, first-served basis,
and the data to be printed is stored in the file system of the host
computer. The remote computers may thus continue processing without
waiting for printing to be completed.
FIG. 2 illustrates the embodiment of the present invention shown in FIG. 1
adapted to allow a local area network (LAN) of remote computers to
function more efficiently by affording to a network file server remote
computer 22A access to the fast disk drive of host computer 10. Remote
computers 22B, 22C, and 22D are the other computers in the network. Each
remote computer 22A-22D is provided with a LAN card 26 which is connected
to an active hub 24 by a plurality of LAN cables 28. One local area
network preferably adapted for use with the present invention is available
from Novell, Inc. of Provo, Utah as the NETWARE.RTM. 286 2.0a system.
In the data communication system illustrated in FIG. 2, file server remote
computer 22A may be based on an Intel 80386 microprocessor. By utilizing
the host disk drive according to the system of the present invention, file
server remote computer 22A realizes up to a three-fold increase in
throughput. In addition, delays which are often experienced in file
transfers and data base applications are reduced. Furthermore, the present
invention improves the performance of some application programs by an
order of magnitude.
In FIG. 2, file server remote computer 22A is provided with a direct
connection to the resources of host computer 10 through interconnecting
cable 16A. A file on the host disk drive thus takes the place of the disk
drive that would normally need to be resident on file server remote
computer 22A. As files on the large host disk drive can be accessed at
very high speed, the present invention allows the local area network to
operate more efficiently.
FIG. 3 shows yet another arrangement of the present invention used in an
alternate manner with the local area network already described. File
server remote computer 22A continues to be connected to host computer 10
by way of interconnecting cable 16A. Another of the remote computers, a
host gateway remote computer 22A, is also provided with a direct
connection to the host computer through remote interface 20B and
interconnecting cable 16B. With one remote computer serving as a file
server remote computer to share the disk drive of the host computer, host
gateway remote computer 22B functions as a gateway to allow all other
remote computers 22C-22D connected to the local area network to have
access to the resources of the host computer and exercise the advantageous
functions mentioned earlier.
A number of remote computers can be added to a local area network, such as
that provided by Novell, Inc. This not only allows a number of remote
computers to have access to all other remote computers on the local area
network, but by way of host gateway remote computer 22B, to also have
access to the resources of host computer 10. Due to the speed at which
data is transferred between host gateway remote computer 22B and host
computer 10, the only delay experienced by the user of a remote computer
on the local area network is due to the delay inherent in the local area
network itself.
All of the above are possible because the present invention establishes a
high-speed communication path between the host and the remote computers.
While the inventive embodiment disclosed incorporates some network-like
functions, it is not a substitute for a local area network, such as that
represented in FIGS. 2 and 3. Rather, the presently preferred embodiment
augments and enhances the functions of a local area network.
A specific structure of a presently preferred embodiment of the present
invention will now be described as adapted for use with host computers
available from Icon International, Inc. of Orem, Utah utilizing the
Motorola MC 68020 microprocessor.
Host computers incorporating the MC 68020 microprocessor must include a
host bus structure meeting minimum structural and operational
requirements. Complete information concerning the MC 68020 microprocessor
can be found in the publication entitled MC 68020 32-bit Microprocessor
User's Manual, 2d. Ed. (1985), and later editions, which are available
from Prentice Hall Publishers, which are incorporated herein by reference.
Particular information concerning the bus structure of the host computer
systems available from Icon International, Inc. is available from
documentation pertaining to each specific computer system and in United
States patent application Ser. No. 074,310, which is incorporated herein
by reference.
As will be explained shortly, extremely fast data transmission between a
host computer and one or more remote computers is possible according to
the teachings of the present invention by creating a parallel data
transmission path from the host bus in the host computer to the remote bus
in the remote computer. The use of the structures herein described to form
this "bus-to-bus" communication pathway allows extremely fast data
transfer between a host computer and one or more remote computers without
the time-consuming bottlenecks often found in local area networks,
bottlenecks resulting from time-intensive tasks such as packetization and
network arbitration.
The Host Interface
FIG. 4 is a block diagram showing the structures of one embodiment of host
interface 12 incorporating teachings of the present invention. Consistent
with FIGS. 1-3, it is preferred that host interface 12 be placed on a
single circuit board, and that six (6) host ports 110A-110F be provided on
each board. Other numbers of host ports, as well as other configurations
for the host interface, are considered to be within the scope of the
present invention.
A host bus 100, including thirty-two (32) lines serving as address lines,
thirty-two (32) lines serving as data lines, and other control lines, is
the principle bus of host computer 10. The MC 68020 microprocessor is
connected to host bus 100, and when access to a remote device is desired,
the address of that device is first presented on host bus 100 followed by
the presentation thereon of digital data from or destined to the addressed
device. With a host computer 10 utilizing a MC 68020 microprocessor, the
host bus structure is dictated by the requirements of the MC 68020
microprocessor.
Host interface 12 receives all thirty-two (32) of the address lines and
sixteen (16) of the data lines contained on host bus 100. A control
circuit 104 in host interface 12 receives bits 16-31 of the address by way
of an upper address bus 130. The remaining address bits 0-15 are presented
to a multiplexer 116 by way of a lower host address bus 126. As will be
explained in greater detail shortly, bits 16-31 on upper host address bus
130 select one host port 110A-110F, while bits 0-15 on lower host address
bus 126 are passed directly by way of multiplexer 116 to the selected host
port 110A-110F for selecting one address of a location in the random
access memory location provided on the remote interface.
For maximum efficient and versatile operation, each host port 110A-110D
provided in host interface 12 is addressed as a logical device, just as
any memory space is addressed in the logical memory space of host computer
10.
In the inventive embodiment using the host computers previously identified,
address space has been reserved for host interface 12 beginning at
hexadecimal address E0000000 and extending through hexadecimal address
E0FFFFFF. Each host port 110A-110F is allocated 128K of logical memory
space. With the previously indicated address space being reserved, in host
interface 12 there may be a maximum of 128 host ports on the embodiment
disclosed.
Provided below in Table A is the summary of potential address allocations
for a representative number of the host ports.
TABLE A
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HOST PORT 0 E0000000 TO E001FFFF
HOST PORT 1 E0020000 TO E003FFFF
HOST PORT 2 E0040000 TO E005FFFF
. . .
. . .
. . .
HOST PORT 127 E0FE0000 TO E0FFFFFF
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The addressing scheme suggested in Table A allows communication between the
host computer and the host interface to occur at the port level. That is,
there are no special address spaces associated with the functions between
the host computer and the various host interface cir | | |
