Electrical computers and digital processing systems: memory – Storage accessing and control – Specific memory composition
Reexamination Certificate
1997-05-30
2002-05-14
Nguyen, Than (Department: 2759)
Electrical computers and digital processing systems: memory
Storage accessing and control
Specific memory composition
C711S003000, C711S004000, C711S111000, C711S112000, C711S115000, C711S117000, C711S118000, C711S138000, C711S150000, C711S170000, C711S171000, C711S172000, C711S173000, C710S022000, C710S023000, C710S027000
Reexamination Certificate
active
06389509
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention pertains to the field of performance enhancing devices for CD-ROM devices and other slow access memory devices.
CD-ROM devices, and other devices like magneto-optical disk drives and tape drives are notoriously slow in accessing data. For example, in so called 1×CD-ROM devices typical access times are 390 milliseconds (hereafter msec) and data transfer rates are typically 150 kilobytes/second (hereafter KB/sec). Even so called 2×CD-ROM drives are not much faster, averaging 200-290 msec access times and 300 KB/sec transfer rates, and 4×devices average 190 msec access time and 600 KB/sec transfer rates.
In an attempt to alleviate this problem, manufacturers of CD-ROM devices have been incorporating random access memory into their devices to help speed up access. The random access memory is managed as a cache. Typical cache sizes of up to 256 kilobytes of random access memory have been used. The probem with this approach is that the capacity for data storage in CD-ROM devices is so huge, that a 256 kilobyte (hereafter KB) cache does not significantly speed up access. For example, typical data transfer rates for a 1×CD-ROM with a 256 KB cache are only speeded up to 170-180 KB/sec and 4×device have their data transfer rates speeded up to only 700 KB/sec.
In another approach to solving this problem, some manufacturers such as Insignia Software Solutions, with its RapidCD software product, have introduced drivers for CD ROM devices which use the hard disk and RAM of the host computer as look-ahead cache memory. Another example of this type of product is the CD-ROM Toolkit by FWB Software, Inc. The problem with this approach (which will be called the software cache approach herein) is that using part of the host hard disk and RAM for cache purposes for the CD-ROM device lowers the capacity of the host hard disk and RAM for other purposes such as storing application programs and data. In many cases, especially where a multitasking environment is in effect such as in Windows and Macintosh environments, the remaining space on the host hard disk and RAM is insufficient to support all necessary operations. Further, although a program may initially run, it may ultimately crash as more demands on the host RAM and hard disk for storage are made. This can lead to loss of whatever data is currently displayed which has not yet been saved to hard disk.
The software cache approach also requires that the host CPU be used to manage the cache such as reading the least recently used table, storing data into the cache, intercepting read requests and examining the cache map and extracting data from the software cache or from the CD-ROM as appropriate.
The software cache approach also utilizes the file operating system of the host. Typically, such operating system functions require a fairly large amount of overhead even for a simple data transfer.
Also, software cache operation is not universally compatible with all operating systems and hardware platforms.
The software cache approach is also not terribly efficient, because to store data in the host hard disk cache area, the data is first transferred from the CD-ROM into the host RAM, and from there into the host hard disk cache area. This two step process involves overhead for each of the two storage transactions and ties up the host CPU, the host RAM and the host hard disk thereby precluding these assets from being used for other multitasking purposes during the transactions.
Accordingly, a need has arisen for a method and apparatus to vastly speed up access times and data transfer rates for slow access time rotating media bulk storage memory devices which solves the above noted problems and is completely transparent to the host computer.
SUMMARY OF THE INVENTION
According to the teachings of the invention, there is disclosed herein a controller for a slow access time rotating media bulk storage memory devices such as a CD-ROM drive or magneto-optical read/write drive which uses a conventional large-capacity, rotating-magnetic-media type hard disk as a cache.
The bulk memory storage device controller system comprises the following elements in combination. A first bus controller for the rotating media bulk storage memory device is located within the controller and is coupled to an external rotating media bulk storage memory device via a first bus and a first bus port. In some embodiments, the rotating media bulk storage memory device may be integrated within the same housing which contains the bulk memory storage device controller system. Typically, the rotating media bulk storage memory device is coupled to the first bus controller by a SCSI bus but the bus can be any known bus or any bus developed in the future. The first bus controller serves to manage data transfers to and from said rotating media bulk storage memory device in the manner said data transfers are normally accomplished over the first bus.
A second bus controller is located within the controller system and is coupled to a second bus port. A conventional large-capacity, rotating-magnetic-media type hard disk is coupled to the second bus controller via the second bus port and a second bus. This conventional large-capacity, rotating-magnetic-media type hard disk may be integrated within the bulk memory storage device controller system or may be external to it.
A third bus controller is located within the controller system and is coupled to a third bus port. A conventional host computer such as a PC, Macintosh etc. is coupled to the third bus controller via the third bus port. The function of the third bus controller is to control data transfers back and forth between the host computer and the controller system via the third bus and to present to the host computer a conventional CD-ROM etc. interface. That is, if the bulk storage device is a CD-ROM, the third bus controller serves to present a conventional CD-ROM interface to the host computer such that the fact that a hard disk cache is used is transparent to the host computer in the sense that the CD-ROM driver software need not include any instructions or commands that accomodate the presence of the hard disk cache. To the host computer CD-ROM driver software, the controller system according to the invention looks simply like a CD-ROM drive except it is faster.
A memory within the system controller stores program instructions and data needed by the microprocessor to be described next. In most embodiments, the program instructions are stored in non-volatile memory such as EPROM, and the data is stord in volatile static RAM. In alternative embodiments, the program may be stored on the conventional rotating-magnetic-media type hard disk and read out and stored in the RAM at power-up.
A microprocessor is coupled to the memory and the first, second and third bus controllers via data, control and address buses and serves to execute the program instructions stored in the memory. The program controls the microprocessor to manage the controller system such that the conventional rotating-magnetic-media type hard disk implements a cache memory function for the conventional rotating media bulk storage memory device. The program controls the microprocessor to copy at least some of the data from said rotating media bulk storage memory device to said conventional rotating-magnetic-media type hard disk whenever a new rotating media is inserted into said rotating media bulk storage memory device. The program also controls the microprocessor to keep a record in said memory of what blocks of data from said rotating media bulk storage memory device have been stored in said rotating-magnetic-media type hard disk and the addresses thereof in the rotating-magnetic-media type hard disk. In the preferred embodiment, the hard disk cache has one area devoted to cloning, i.e., making a duplicate of all or some subset of the blocks of data on a CD-ROM disk, and has another area managed as a cache memory. In such an embodiment, there is a clone map which consists of approximately 1400 bytes in a
Berenguel Leo
Korpi James E.
Lin Conne
Hill Robert Charles
Nguyen Than
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