4,868,737

4,868,737
United States Patent [191
[11]
[45]
Soederlund
Patent Number:
Date of Patent:
[54] METHOD AND ARRANGEMENT IN WHICH
CAPACITY OF A RELATED STORAGE
MEDIUM IS CHECKED WHEN BUFFERING
DATA
[75] Inventor:
Tom 0. Soederlund, Oslo, Norway
[73] Assignee:
Tandberg Data A/S, Oslo, Norway
[22] Filed:
[30]
dently of the physical storage capacity of the buffer
memory, the logical storage capacity thereof is dynami
[51]
01001.4 .............................................. .. soar 3/00
us. 01. ................................... .. 364/200; 364/239
[58]
Field of Search
364/200 MS File, 900 MS File
U.S. PATENT DOCUMENTS
Heath ...................... ..
4,486,854 12/1984 Yuni et a1.
4,618,926 10/1986
cally adapted to the storage capacity of the data store
which is still available. As long as the available storage
capacity of the data store is greater than a maximum
physical storage capacity of the buffer memory, the
buffer memory remains unmodi?ed. When, however,
the storage capacity still available in the data store be
References Cited
3/1981
ABSTRACT
Fed. Rep. of Germany ..... .. 3644008
[52]
4,258,418
Simpson
provided in the data store and its storage capacity is
exhausted, the data still contained in the buffer memory
might not be recorded on the storage medium. Indepen
Foreign Application Priority Data
[56]
“System for Control of Residual Byte Counting”, Jun.
7, 1983, vol. 7, No. 130.
“Buffer Register”, Jun. 29, 1982, vol. 6, No. 116.
Primary Examiner-Raulfe B. Zache
Attorney, Agent, or Firm—I-Iill, Van Santen, Steadman &
In a system for buffering data, a buffer memory is pro
vided for buffering data output from a data source to an
asynchronous data store. When a storage medium is
Jul. 6, 1907
Dec. 22, 1986 [DE]
Sep. 19, 1989
OTHER PUBLICATIONS
[57]
[21] Appl. No.: 70,056
4,868,737
.. 364/200
.. 364/900
Kubo et al. ....................... .. 364/200
comes less than the maximum storage capacity of the
buffer memory, its logical storage capacity is reduced
so that all data intermediately stored in the buffer mem
ory can still always be stored on the storage medium.
FOREIGN PATENT DOCUMENTS
9 Claims, 1 Drawing Sheet
0017670 10/1980 European Pat. Off. .
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Patent
4,868,737
Sep. 19, 1989
BUFFE
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1
4,868,737
2
The modi?cation of the possible storage capacity of
the buffer memory can occur linearly or in steps, and in
METHOD AND ARRANGEMENT IN WHICH
CAPACITY OF A RELATED STORAGE MEDIUM
IS CHECKED WHEN BUFFERING DATA
the simplest case, in one step.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block circuit diagram illustrating a trans
mission of data to a data store;
FIG. 2 is a schematic illustration of a magnetic tape;
FIG. 3 is a schematic illustration of the possible stor
age capacity of the buffer memory;
FIG. 4 is a graphic illustration of the possible storage
capacity of the buffer memory dependent on the avail
BACKGROUND OF THE INVENTION
1. Field of the Invention:
The invention is directed to a method for buffering
data wherein data are transmitted from a data source to
a data store and are stored there on a storage medium
having a variable available storage capacity. A buffer
memory is provided for intermediate storage of the
data. The buffer memory has a prescribed physical
storage capacity.
2. Description of the Prior Art:
able storage capacity of the storage medium; and
FIG. 5 is a block circuit diagram of an arrangement
15 for the implementation of the method.
In a transmission of data from a data source to an
DESCRIPTION OF THE PREFERRED
asynchronous data storage, the use of a buffer memory
EMBODIMENTS
between the data source and the data storage is re
In the illustration in FIG. 1, data to be stored in a
quired. The data storage records the data on a storage 20 storage medium of a data store DST are output as data
medium which can be designed as a magnetic storage
D from a data source D8 which can be a computer or a
medium such as a magnetic tape, ?oppy disk or mag
host. The data store DST is fashioned as an asynchro
netic disk, or which can be fashioned as an optical plate
nous storage and the data D are supplied to the data
or paper. When the storage medium is full, i.e. when
store DST as write data Dl via a buffer memory B in
there is no longer any space for storing data, there is the
order to adapt the transmission rate of the data D output
risk that data which are still situated in the buffer mem
from the data source DS to the recording speed of the
ory could be lost. This problem increases with increas
data store DST.
ing size of buffer memory.
There is then the risk in such a transmission that,
when the available storage capacity on the storage me
SUMMARY OF THE INVENTION
30 dium is smaller than the storage capacity of the buffer
It is therefore an object of the invention to specify a
memory B, all data intermediately stored therein can no
method and an arrangement with the employment of
longer be recorded on the storage medium.
which it is assured that all data present in a buffer mem
The buffer memory B is therefore operated such that
ory are still always capable of being recorded on the
it should never contain more data D than can still be
storage medium.
35 recorded on the storage medium. Otherwise the risk is
In a method of the type initially cited, this object is
present that the data D are lost, when, for example, the
achieved by modifying the currently available storage
storage medium is taken from the data store DST, or the
capacity of the buffer memory dependent on the avail
buffer memory B does not have its own power supply
able storage capacity of the storage medium. Accord
ingly, the currently available storage capacity of the
buffer memory is equal to its physical storage capacity
which is independent of the power supply of the data
40 store DST, or when a transmission of the data D which
could does not provide a renewed transmission of the
data D which could no longer be recorded.
In the illustration in FIG. 2, a magnetic tape is pro
as long as the available storage capacity of the storage
medium is greater than this physical storage capacity of
the buffer memory. The currently available storage
capacity of the buffer memory is dynamically dimin
ished when the available storage capacity of the storage
medium is less than the physical storage capacity of the
buffer memory. Thus, all data stored in the buffer mem
ory are always storable on the storage medium.
Printers or plotters which record the data on paper,
magnetic data stores which record the data on a mag
netic tape, on a ?oppy disk or on a magnetic disk, and
optical storages which record the data on an optical
disk can also be employed as data stores.
As long as the storage capacity still available on the
recording medium is greater than the physical storage
45
vided as storage medium M, this magnetic tape, for
example, being contained in a cassette. At the beginning
and at the end, the magnetic tape contains holes BOT
which identify the beginning of the magnetic tape, one
hole LP which identi?es a loading point, one hole EW
which represents an early warning, and holes EOT
which identify an end of the magnetic tape. For exam
ple, the magnetic tape is written in nine tracks and the
last track will then end with the recognition of the ?rst
hole EOT. Although the end of the medium is de?ned
as the early warning EW of the last track, it is possible
that about 90 data blocks each having QKB are still to be
recorded onto the magnetic tape after this point has
been reached When, in the least favorable case, all
capacity of the buffer memory, then in this situation, the
entire logical storage capacity of the buffer memory is
blocks must be recorded 15 times before they are cor
available. When, however, the storage medium only has
rectly recorded, then only two to three blocks can be
an available storage capacity which is smaller than the 60 recorded. It would thus not be possible to still record all
physical storage capacity of the buffer memory, then
90 data blocks on the magnetic tape. There is thus the
risk that data blocks will be lost and this risk increases
the entire storage capacity of the buffer should no
with increasing size of the buffer memory. Existing
longer be used. Rather, the possible logical storage
magnetic tape recorder devices for magnetic tape ac
capacity of the buffer memory is dynamically reduced
in accordance with the storage capacity of the storage 65 commodated in cassettes have buffer memories up to 16
KB, and there is the risk that given such large buffer
medium which is still available. It is assured in this way
that all data present in the buffer memory are still al
ways capable of being recorded on the storage medium.
memories, not all data contained therein can still be
recorded on the storage medium M.
3
4,868,737
4
than the physical storage capacity P of the storage unit
The illustration in FIG. 3 schematically shows the
possible logical storage capacity of a storage unit ST
present in the buffer memory and shows the respec
ST. In a magnetic tape recorder, for example, this can
occur since the clock pulses that are output by a drive
motor for the magnetic tape are counted, or since the
time during which the magnetic tape is moved in one
direction at nominal speed is measured. It is also possi
ble, for example, to count the drive pulses of a motor
designed as a stepping motor. In any case, the length of
tively occupied storage capacity R and the available
storage capacity A of the storage medium M. When the
available storage capacity of the storage medium M is
greater then the physical storage capacity P of the stor
age unit ST, the possible or currently available logical
storage capacity L corresponds to the physical storage
the magnetic tape already recorded is measured and,
since the full length of the magnetic tape is known, the
capacity P. This is the case is the two illustrations at the
left. When the available storage capacity A is smaller
than the physical storage capacity P of the buffer stor
age unit ST, the possible or currently available logical
storage capacity L of the buffer storage unit ST is corre
spondingly limited, so that the full physical storage
capacity P thereof is no longer available. This is shown
storage capacity A which is still available can be identi
?ed therefrom. When this available storage capacity A
is less than the physical storage capacity P, the data
store DST emits a signal S1 to the buffer memory so
that it is set to a smaller logical storage capacity L by
use of the control unit CU. Whenever the storage unit
ST is full, the storage control CU emits a signal S2 to
the data source DS in order to inform the latter that the
buffer memory B cannot accept any further data. It is
This relationship is graphically shown in the illustra 20 assured in this may that all data intermediately stored in
tion in FIG. 4. The available storage capacity A of the
the buffer memory B can always still be recorded onto
storage medium M is shown in the abscissa direction
the storage medium M.
in the two illustrations at the right. What is assured in
this way is that the full content of the storage unit ST
can still always be stored on the storage medium M.
and the logical, possible storage capacity L of the buffer
The buffer memory B can then contain a storage unit
memory B is shown in the ordinate direction. As long as
ST whose storage capacity is signi?cantly greater than
the available storage capacity A is greater than the 25 16 kilobytes and it can nonetheless be assured that no
physical storage capacity P of the storage unit ST, the
data will be lost in the buffer memory B.
physical storage capacity P is also the logical, possible
Although various minor changes and modi?cations
storage capacity L of the buffer memory B. When,
however, the available storage capacity A of the stor
might be proposed by those skilled in the art, it will be
age medium M becomes smaller than the physical stor 30 understood that I wish to include within the claims of
the patent warranted hereon all such changes and modi
age capacity P of the storage unit ST, the logical, possi
?cations as reasonably come within my contribution to
ble storage capacity L of the storage unit ST is corre
the
art.
spondingly reduced. This reduction can occur linearly
I claim as my invention:
dependent on the storage capacity A, or can also occur
in steps, for example, in single-stepped fashion.
35
When recording data D1 onto the storage medium M,
the storage capacity of the buffer memory B is always
equal to the logical storage capacity L of the storage
unit ST as seen proceeding from the data source DS,
whereas the data store DST always sees the buffer
memory B with its full physical storage capacity P. A
data transmission from the data source DS to the buffer
memory B is only possible when fewer data are stored
in the buffer memory B then corresponds to the respec
tive logical storage capacity L. It is thus assured that no 45
more data than can be recorded on the storage medium
M are stored on the buffer memory B at any time. When
the storage medium M is full, the buffer memory B is
employ and no data are lost.
Given the arrangement shown in FIG. 5 for the im
plementation of the method, the data output from the
data source D8 are supplied to the buffer memory B
which has a control unit CU in addition to the storage
unit ST, this control unit CU controlling the write-in
1. A method for buffering data, comprising steps of:
transmitting data from a data source to a data store
via a buffer memory, a storage medium of the data
store having a variable available storage capacity
and the buffer memory having a prescribed physi
cal storage capacity; and
modifying a currently available storage capacity of
the buffer memory dependent on the available stor
age capacity of the storage medium such that the
currently available storage capacity of the buffer
memory is equal to said physical storage capacity
thereof as long as the available storage capacity of
the storage medium is greater than said physical
storage capacity of the buffer memory, and
wherein the currently available storage capacity of
the buffer memory is dynamically diminished when
the available storage capacity of the storage me
dium is less than said physical storage capacity of
the buffer memory, so that all data stored in the
buffer memory are always storable on the storage
medium.
and the read-out of the data D. Buffer memories B 55
2. A method according to claim 1 wherein the cur
which have a constant logical storage capacity are gen
rently available storage capacity of the buffer memory
erally known and are fashioned, for example, as what
is modi?ed in steps.
are referred to as FIFO memories (First In First Out
3. A method according to claim 1 wherein the cur
Memories). The control unit CU is modi?ed in compari
rently available storage capacity of the buffer memory
son to a known control unit such that it is also possible
is modi?ed in single steps.
to write the data D in at some other location, given, for
4. A method according to claim 1 wherein the avail
example a FIFO memory, in order to modify the logical
able storage capacity of the storage medium of the data
storage capacity L.
store is identi?ed and is communicated to the buffer
The data store DST, for example, is designed as a
magnetic tape recorder and contains a magnetic tape as 65 memory.
a storage medium M. The data store DST further con
5. A method for buffering data, comprising steps of:
tains a detector DE which recognizes when the avail
able storage capacity A of the storage medium M is less
transmitting data from a data source to a data store
via a buffer memory, the data store having a stor
5
4,868,737
6
control means can reduce the currently available
age medium having a variable available storage
storage capacity of the storage unit.
capacity; and
reducing available storage capacity of the buffer
7. A system according to claim 6 wherein said storage
medium of said data store is selected from a group con
memory to be less than said maximum storage ca
sisting of a magnetic storage, an optical storage, a
printer, or a plotter.
pacity dependent on the available storage capacity
of the storage medium such that the maximum
8. A system according to claim 6 wherein said data
store storage medium comprises a magnetic tape re
storage capacity of the buffer memory is provided
corder and said detector means identi?es a length of a
as long as the available storage capacity of the
buffer memory, and wherein the available storage
magnetic tape serving as said storage medium which is
still respectively available for recording on.
capacity of the buffer memory is dynamically di
minished below the maximum capacity when the
variable storage capacity of the storage medium is
less than said maximum storage capacity of the
9. A system for buffering data, comprising:
a data source connecting to a data store through a
buffer memory;
said buffer memory having a control means and a
buffer memory, so that all data stored in the buffer
memory are always storable on the storage me
storage unit, said control means selectively reduc
ing a currently available storage capacity of said
storage unit below a maximum storage capacity
thereof; and
dium.
6. A system for buffering data, comprising:
a data source connecting to a data store through a 20
buffer memory;
said data store having a storage medium and a detec
tor means, said detector means identifying an avail
able storage capacity of the storage medium and
said buffer memory having a control means and a
outputting a signal to said control means when the
storage capacity of said storage unit; and
said data store having a storage medium and a detec 25
tor means, said detector means identifying an avail
able storage capacity of the storage medium and
available storage capacity is less than said maxi
mum storage capacity of said storage unit so that
said control means can then reduce the currently
available storage capacity of the storage unit so
outputting a signal to said control means when the
that all data stored in the buffer memory can be
available storage capacity is less than a physical
storage capacity of said storage unit so that said 30
stored in the storage medium.
35
45
55
65
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