Static information storage and retrieval – Powering – Data preservation
Reexamination Certificate
2000-12-01
2002-10-29
Elms, Richard (Department: 2824)
Static information storage and retrieval
Powering
Data preservation
C365S229000, C700S293000, C714S014000, C714S022000
Reexamination Certificate
active
06473355
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to electronic data storage and, more particularly, to structures for long-term storage of data in volatile memory.
BACKGROUND OF THE INVENTION
Computer systems, regardless of manufacturer or size, typically employ at least the following fundamental components: a central processing unit (CPU); a display device; at least one user input device; and memory for data storage.
There are two basic classifications of memory: volatile memory and non-volatile memory. The primary difference between volatile memory and non-volatile memory is that a volatile memory needs to be supplied with external power in order to hold and refresh data while a non-volatile memory can maintain data for extended periods of time without any power being supplied to the device. Consequently, data stored in volatile memory are typically lost when power to the host computer system is removed or cut-off, while data stored in non-volatile memory are typically retained when power to the host computer system is removed or cut-off.
Most computer systems utilize both volatile and non-volatile memory in the same system or device. For instance, in a typical computer system, data intended for high-speed short-term access, such as on-chip memory for the CPU, and often first and second level off-chip memory, are typically stored in volatile memory devices such as a cache or random access memory (RAM, DRAM, SRAM etc.) which typically have nanosecond to microsecond access times. However, in the same computer system, data intended for long-term storage or “mass storage” are typically stored in non-volatile storage devices such as magnetic disks, hard disk drives, zip drives, floppy disk drives, tape drives and optical storage media which typically have access times on the order of milliseconds or seconds.
As discussed above, volatile memory devices typically have significantly faster access times and higher data transfer rates than non-volatile storage devices. This, coupled with the decreasing cost of volatile memory over the past few years, makes volatile memory devices more desirable than non-volatile storage devices for use with high-speed systems. One reason non-volatile storage devices are so much slower than volatile memory devices is that non-volatile storage devices, such as disk drives, typically have moving parts and mechanical components such as rotating hard disks, rotating optical disks, rotating floppy disks, optical or magnetic readers, floating heads, lasers, tape drives and tape.
The mechanical components associated with non-volatile storage devices are problematic for several reasons. First, mechanical components slow down data transfer significantly because no mechanical mechanism is capable of achieving data transfer rates approaching the speed of a pure signal transfer between electronic components, i.e., electrical signals travel faster than any mechanical device can move. Second, mechanical components are subject to friction and motion stress and, therefore, even the best components physically wear out and degrade over time. This fact creates a long-term reliability problem and virtually guarantees that parts will need to be replaced in the field. In addition, to overcome friction and other mechanical forces, mechanical components typically require more power and therefore use up power resources faster. This is particularly disadvantageous in the present market that stresses compact size, including smaller battery packs and power supplies, as well as portability, lightweight and extended operation capability.
For the reasons discussed above, non-volatile storage devices are typically slower, less reliable and need more power to function than volatile memory devices. In contrast to non-volatile storage devices, volatile memory devices typically do not employ any moving parts or mechanical components. Therefore, volatile memory devices are faster, more reliable and need less power for operation than non-volatile storage devices. Consequently, volatile memory devices are potentially more desirable than non-volatile storage devices and represent an appealing alternative to non-volatile memory for computer systems requiring highly reliable data access at high-speeds with minimal power used.
As discussed above, volatile memory has numerous advantages in terms of speed, reliability and power consumption over non-volatile memory and non-volatile storage devices. However, the vast majority of long-term memory devices used in the prior art were non-volatile storage devices such as hard disk drives, zip drives and optical media. This industry-wide use of non-volatile memory for long term storage, despite the potential advantages of volatile memory, is primarily the result of the fact that using prior art volatile memory devices for long-term data storage involved unacceptable inherent risks, slow transfer rates between the host computer system and the memory and the addition of significant equipment resulting in significant additional cost.
FIG. 1
shows a typical prior art sub-system
100
. Prior art sub-system
100
includes: motherboard
110
; host computer system power supply
101
; DC power connector
112
, coupling motherboard
110
to power supply
101
; AC power connector
157
, coupling commercial AC power from outlet
199
to host computer system power supply
101
; DC power connector
103
, coupling power supply
101
to a non-volatile storage device
105
(typically a hard disk drive or optical storage device); disk controller
109
; and a single data cable
107
that facilitates the exchange of data between non-volatile storage device
105
and disk controller
109
.
In prior art sub-systems, such as sub-system
100
of
FIG. 1
, when power to sub-system
100
was shut down in a controlled and orderly manner no data were typically lost However, when power was cut-off to the computer system, for any reason, the volatile memory lost all its data. Thus, using prior art volatile memory devices: if power was cut-off to the computer system in an unplanned manner, such as the user inadvertently unplugging the computer system or, in the case of a laptop or other portable system, allowing the battery to run down, all the data were lost; if power was interrupted by a local power failure such as a blown fuse or circuit breaker, all the data were lost; or if power was interrupted by a major power failure at a relay station or other power company source, all the data in volatile memory were lost. Consequently, using prior art volatile memory devices for long term data storage meant running the risk that even a temporary interruption of power would mean losing data forever.
In some prior art systems, a standard disk bus was used in an attempt to back up volatile memory to a dedicated disk drive. These prior devices addressed some of the problems discussed above. However, since these prior art devices employed dedicated disks and used standard disks buses, the devices were typically expensive to employ and had relatively slow data transfer rates between the host computer system and the memory device.
What is needed is a structure that allows a host computer system to use volatile memory as the storage media, i.e., allows use of volatile memory as if it were a disk drive. The structure should also provide the stability and security of non-volatile memory and, ideally, connect to an expansion bus of the host computer system, such as a PCI bus, to provide a sub-system that is faster than prior art systems at a relatively low cost.
SUMMARY OF THE INVENTION
According to the principles of the present invention, volatile memory devices are provided that are used by the host computer system as the storage media, i.e., they are used as if it were a disk drive. The volatile memory devices of the invention include an integrated controller and volatile memory storage media.
The volatile memory devices of the invention also include a volatile memory device power supply and back up system to provide power to both the volatile memory and non-volatile memory in the e
Genatek, Inc.
Gunnison McKay & Hodgson, L.L.P.
McKay Philip J.
Nguyen Van-Thu
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