Electrical computers and digital processing systems: memory – Storage accessing and control – Access timing
Reexamination Certificate
2001-07-18
2003-01-07
Nguyen, Than (Department: 2187)
Electrical computers and digital processing systems: memory
Storage accessing and control
Access timing
C711S150000, C711S151000, C711S167000, C710S058000, C710S060000, C710S061000, C709S208000, C709S211000
Reexamination Certificate
active
06505281
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates in general to computer systems and mass memory systems, and more particularly to a programmed processor controlling a number of memory modules utilizing a high-speed and wide band data bus for sequentially reading and writing data with regard to the memory modules. The invention also relates to a controller operating in conjunction with a host system, but transparent thereto, for controlling the mass memory system.
BACKGROUND OF THE INVENTION
A memory system of some type is a necessity for the operation of a computer or programmed processor. In addition to the need for a scratch pad type of memory, computers are often also provided with a non-volatile media for either the archival storage of data or for the storage of large amounts of data that are periodically required by the processor. The non-volatile media for storing large amounts of data often include magnetic tape stored on reels. The magnetic tape medium is relatively inexpensive, but the reading and writing of data therefrom is slow. Indeed, when used as a back-up medium for archival purposes, it often takes several hours to provide a complete back-up of a day's data. During the back-up operation, the host system is inaccessible to a user and thus dedicated to the archival back-up function. For this reason, the back-up function is usually carried out after business hours. Any memory failure during the normal business hours thus results in lost data, as no back-up is yet available. Moreover, although the magnetic tape medium is somewhat portable, it is bulky, heavy and can be damaged by external magnetic fields.
Another popular non-volatile storage medium comprises magnetic disks and corresponding disk drive systems. Although hard disk drives are well developed and enjoy a high degree of popularity, such a storage medium is nonetheless prone to mechanical failure, neither the hard disks nor the drive systems themselves are removable, the read and write speeds are much slower than the processing systems, and disk drive systems require a disk operating system (DOS) for organizing the data storage on the magnetic disks.
Floppy disks do indeed provide a portable medium for the non-volatile storage of data. The floppy disks themselves provide a low cost medium, but the access time to such type of disks is slower than that of the hard disk drives, the data is less densely stored thereon and it is not practical to store large amounts of data on the floppy-type disk, as many such disks would be required.
There currently are available disk drive systems that provide mirrored back-up data for archival purposes. Such systems are available from Western Digital Corporation and the Connor Peripheral Company. These systems do provide a continuous back-up of data, but such type of systems are not portable to the user, are not easily expandable to accommodate significant amounts of data, and the host computer system must be programmed to mirror the data, thus reducing the time allowed by the system to carry out its normal programming. Another arrangement for storing data on hard disk drives is known as a redundant array of inexpensive disks, i.e., RAID. A redundant array of independent disks is a disk array in which part of the storage capacity over several disks is used to store redundant information about the user data. The redundant information enables regeneration of user data in the event that one of the array's member disks or the access path to it fails. The RAID system employs “striping” which is the storage of different pieces of a portion of data across plural disks. Further, such a system employs exclusive-or parity of the bits and thus is really a fault tolerant system, and does not redundantly store data. The host computer system employing the RAID technique still requires processing time of the host and thus user applications are executed at a slower pace.
There presently exists removable media cartridges that can store upwardly of 100 megabyte-150 megabyte of data. Such systems are known as “Bernoulli” cartridges, obtainable from Cyquest, Inc. The removable cartridges are low cost, but slower than hard disk drives, less reliable, can't be mirrored by the operating system and thus are not continuously mirrored as back-up data. The CD ROM is becoming a well embedded technology for storing upwardly of 500-700 megabytes of data. However, this non-volatile storage medium can only be read and not written, and the data transfer rate is relatively slow. A CD juke box is equipped to handle more than one CD, but such systems are nevertheless large and bulky, expensive and the media is not updatable.
A relatively new medium for the non-volatile storage of mass data is the read/write optical system, better know as a magneto-optical memory system. Although, the storage density of this type of medium is relatively large, i.e., about 1.3 gigabyte, such systems are relatively expensive, bulky and are not known as high speed access systems
Many mass storage memory systems, and particularly the disk drive systems, require a disk operating system for managing and organizing the data stored on the various sectors of a disk. Typical functions carried out by the DOS software are the allocation of appropriate sectors to particular files, the writing of files into various sectors, the compaction of gaps caused by repeated deletion of files, the maintenance of a file directory, the amount of free space left on the disk, the creation of new files, the deletion of old files, the renaming of existing files, etc. Notwithstanding the complexity of the software of a disk operating system, the mechanical movement of the head of the disk drive accounts for the majority of time in accessing data and transferring the data between the disk storage unit and the host system. Because of the overhead involved in controlling disk drives, host CPUs normally include a separate disk controller for carrying out the disk operating system, thus freeing up the CPU for other data processing functions. Hard disk controllers are conventionally available as separate integrated circuits that provide data transfer rates upwardly of 16-25 Mbit/second.
Buses initially developed for interfacing hard disk drives to host computer systems include the small computer systems interface (SCSI) bus. Since the initial development thereof, the SCSI bus has become a general-purpose standard, capable of supporting multiple processors and up to eight peripheral devices. In the SCSI bus, there are eight data lines plus a parity line, in addition to other signal lines. Data transfers in the synchronous mode can take place up to 10 Mbyte/second. Despite the high speed nature of the SCSI bus, it is not fully utilized, due primarily to the mechanical access time of the disk drive, whether it be a hard disk drive or a floppy disk drive. Therefore, unless the host CPU is busy with other data processing functions, it is necessarily involved in waiting for data from the disk drive unit.
From the foregoing, it can be seen that many of the mass storage media is capable of storing large volumes of data, but generally such mediums are slow speed devices which impair the throughput and overall efficiency of the host CPU. It can therefore be seen that a need exists for a data storage and retrieval system that is high speed, continuously mirrored for back-up purposes, is portable to the user, and is adapted for use with any general purpose computer operating with a hard disk drive unit. A further need exists for a hard disk drive replacement unit that operates transparent to the host computer, via a conventional bus, such as an SCSI bus.
Another need exists for a multiple hard disk drive system that can be read or written to supply high speed data to a host computer, via a processor that operates transparent with respect to the host system. An additional need exists for a disk drive replacement unit employing a high speed digital signal processor communicating with multiple, removable hard disk drives, via a high bandwidth data
Chauza & Handley, L.L.P.
Chauza, Esq. Roger N.
Nguyen Than
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