Abstract:
In a storage system having a main storage and a buffer storage accessable by a plurality of requesters, the buffer storage comprises a buffer storage data area having a plurality of storage areas for storing a portion of data of the main storage as a copy of the main storage for each predetermind storage unit, and a buffer storage addess area for storing addresses of the predetermined storage units coresponding to the storage areas. The buffer storage address area is divided into a plurality of addres area banks each interleaved by storage unit, and the buffer storage data area is divided into a plurality of data area banks each interleaved by an access width unit.

Description:
This application is a continuation of our prior co-pending U.S. application Ser. No. 148,859, filed Jan. 27, 1988, now U.S. Pat. No. 4,949,244, issued Aug. 14, 1990. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a storage system having a buffer storage, and more particularly to a storage system suitable for use when a plurality of requesters simultaneously access the buffer storage. 
     In a storage system having the buffer storage, the buffer storage is selected to be of smaller capacity and higher speed than a main storage, and a portion of data stored in the main storage which is most frequently used is stored in the buffer storage so that the data can be quickly accessed through the buffer storage. The buffer storage has a data area for storing the data as well as a buffer storage address area. The buffer storage address area stores addresses of the data stored in the data area and indicates whether or not the data at the accessed address is present in the data area. 
     Where such a buffer storage is directly accessed by a pipelined instruction processor, instruction fetch, operand fetch and operand store requests may be independently issued to the buffer storage and hence those requests may be issued simultaneously. In this case, lower priority instructions are reserved and the execution performance of the instruction processor is lowered. In order to resolve this problem, in USP 4,168,926, each of the address area and the data area of the buffer storage is divided into an instruction fetching area and an operand fetching area which are independently accessible, and an address area for only the operand store is provided. 
     NIKKEI ELECTRONICS, Nov. 18, 1985, pages 241 to 243 discloses a three-hierachy storage system in which an intermediate buffer storage is added between the buffer storage which is directly accessed by the instruction processor and the main storage. Usually, an input/output processor, in addition to the instruction processor, is connected to the intermediate buffer storage. Thus, access requests from those processors may be simultaneously issued. In this case, again, the lower priority access request is reserved. 
     A multi-processor system is disclosed in NIKKEI ELECTRONICS, Nov. 18, 1985, pages 243 and 244. A plurality of instruction processors and a plurality of input/output processors are connected to an intermediate buffer memory and hence the competition between of access requests increases. In order to resolve this problem, it is proposed to provide a plurality of intermediate buffers which are independently operable in order to reduce the competition of access requests. 
     In those prior art systems, a plurality of buffer storages are provided to improve the system throughput. However, in those systems, the amount of hardware increases and a complex control is required to keep the contents of the plurality of buffer storages consistent. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a storage control system which minimizes increase of hardware and reduces competition for access in a buffer storage by a relatively simple control. 
     In order to achieve the above object, in accordance with the present invention, a buffer storage address area is divided into a plurality of banks which are interleaved by a block (a second predetermined storage unit), and a buffer storage data area is also divided into a plurality of banks which are interleaved by an access width (a first predetermined storage unit). 
     With such an arrangement, when a plurality of access requesters access different banks of the buffer storage address area, the buffer storage accesses by the plurality of access requesters can be simultaneously processed and the throughput is enhanced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a block diagram of a computer system to which the present invention is to be applied, 
     FIG. 2 shows a block diagram of a prior art buffer storage, 
     FIG. 3 shows a block diagram of a buffer storage in one embodiment of a storage system of the present invention, and 
     FIG. 4 shows a detailed configuration of the buffer storage of FIG. 3. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Prior to the explanation of the present invention, the configuration of a prior art buffer storage system is explained. FIG. 1 shows a block diagram of a computer system to which the present invention is to be applied. A buffer storage (BS) 6 is connected to a main storage (MS) 8 and to two processors, for example, an instruction processor (IP) 2 and an input/output processor (IOP) 4. 
     FIG. 2 shows a configuration of an address area and a data area of the buffer storage 6 of the prior art system. The buffer storage 6 is connected to two processors 2 and 4. 
     In FIG. 2, the buffer storage comprises a buffer address area 1 and a data area divided into four banks 20-23. Where an access width to each of the banks 20-23 of the data area is 8 bytes, each bank is interleaved by a first predetermined storage unit, i.e. 8 bytes. The processors 2 and 4 independently request accesses of the address area 1 by a first address line 30 and a second address line 31, respectively. Since the address area 1 can process only one request at one time, if two requests are simultaneously issued, one of them is reserved. The request which refers to the address area 1 selectively accesses the banks 20-23 of the data area via data area address lines 40-43. When data is to be read, if the processor 2 requests the access, data read from the accessed bank is transferred to the processor 2 through data lines 500, 510, 520 and 530, and if the processor 4 requests the access, data read from the accessed bank is transferred to the processor 4 through data lines 501, 511, 521 and 531. 
     In the prior art system of FIG. 2, when the two processors simultaneously issue access requests, the lower priority request is reserved. 
     An embodiment of the storage system of the present invention is now explained. FIG. 3 shows a block diagram of a buffer storage in the embodiment in which the present invention is applied to the computer system shown in FIG. 1. 
     In the present embodiment, the address area 1 of FIG. 2 is divided into a plurality of banks, for example, two banks 12 and 13 and the banks are interleaved by a second predetermined storage unit (block). Assuming that one block consists of 64 bytes, addresses of even numbered blocks are registered in an address area bank 12 while addresses of odd numbered blocks are registered in an address area bank 13. Address lines 300, 301 and 310, 311 of first and second access requesters or processors 2 and 4 are connected to the address area banks 12 and 13. When the address of the first access requester specifies an even-number block, the address area bank 12 is referred to by the address line 300, and when it refers to an odd-number block, the address area bank 13 is referred to by the address line 301. For the second access requester, when the address specifies an odd-number block, the address area bank 12 is referred to by the address line 310, and when it specifies an odd-number block, the address area bank 13 is referred to by the address line 311. Data area addresses generated by referencing the address area banks 12 and 13 are supplied to the data area banks 20-23 by data area address lines 400, 410, 420, 430 and the data area address lines 401, 411, 421, 431. In this manner, different data area banks 20-23 can be simultaneously accessed. Further, one of the data area banks can be selectively accessed by the data area address. 
     The operations of the data areas 20-23 and the data lines 500, 510, 520, 530, 501, 511, 521 and 531 are same as those in FIG. 2. 
     In the system of FIG. 3, if the addresses of the first access requester and the second access requester specify different blocks of the address area, the address area banks 12 and 13 can be simultaneously referred to and one of the access requests need not be reserved. Accordingly, the system throughput is improved and the present embodiment is superior to FIG. 2. Further, the amount of hardware of the address area banks 12 and 13 is essentially the same as that of the address area 1 of FIG. 2. 
     Datails of the buffer storage address area banks 12 and 13 and the data area banks 20, 21, 22 and 23 of FIG. 3 are shown in FIG. 4. 
     In FIG. 4, the requester address lines 300, 310, 301 and 311, the address area banks 12 and 13, the data area address lines 400, 410, 420, 430, 401, 411, 421 and 431, the data area banks 20-23, the data lines 500, 510, 520, 530, 501, 511, 521 and 531 are identical to those of FIG. 3. 
     The address area bank 12 comprises a selector 120, an address register 121, address arrays 1230-1233, comparators 1250-1253, a hit row detector 126 and a data area address register 128. The address array is of fourrow structure and the address arrays 1230-1233 correspond to the rows 0-3, respectively. When the addresses on the address lines 300 and 310 of the first and second access requesters specify even-number blocks, the selector 120 selects a higher priority one of the addresses and supplies it to the address register 121. The selection is done by a known priority determination circuit (not shown) which compares the addresses or the address lines 300 and 310, detects the higher priority one and indicates it to the selector 120. The output of the address register 121 is divided into a high order address line 1220 which is connected to rows 1230-1233 of the address array and comparators 1250-1253 for outputs 1240-1243 of the rows, a low order address line 1221 connected to address inputs of the rows 1230-1233 of the address array, and a low order data area address line 1222 connected to the low order of the data area address register 128. The addresses held in the corresponding columns of the rows 1230-1233 of the address array are supplied to the outputs 1240-1243 by the low order address line 1221. The comparators 1250-1253 compare the addresses of the high order address lines 1220 and the addresses supplied from the address array 1230-1233, and when an address specified by the address register 121 is registered in the address array, the row in which it is registered is indicated to the hit row detector 126, which encodes it to generate a row address and supplies it to the high order portion of the data area address register 128 via the row address line 127. The content of the low order data address line 1222 is supplied to the low order portion of the data address register 128 so that the data area address is defined. 
     The configuration of the address area bank 13 is similar to that of the address area bank 12 and it comprises a selector 130, an address register 131, address arrays 1330-1333, comparators 1350-1353, a hit row detector 136 and a data area address register 138. The address area bank 13 operates independently from the address area bank 12. When addresses on the address lines 301 and 311 of the first and second access requesters specify odd-number blocks, the address area bank 13 examines which ones of the address arrays 1330-1333 the addresses are registered in. If they are registered, the data area address is established in the data area address register 138. 
     The data area addresses from the address area banks 12 and 13 are supplied to the selectors 200, 210, 220 and 230 of the data area banks 20-23 and used to access the data area banks. For example, in the data area bank 20, when the data area addresses on the data area address lines 400 and 401 from the address area banks 12 and 13 simultaneously specify the bank 20, the selector 200 selects a higher priority address and supplies it to the data area address register 201 to access the data array 202 of the bank 0. The selection of the higher priority address is done by providing in the data area a priority determination circuit similar to that used in the address area. 
     When the data area addresses from the address area banks 12 and 13 specify different ones of the data area banks 20-23, the data arrays of those banks can be simultaneously accessed. 
     When data is to be read from the data area, for example, when data is to be read from the data area bank 20, the data read from the data array 202 is supplied to the data register 203 and it is sent to the access requester, that is, the processor 2 or 4 through the data line 500 or 501. The operations of other data area banks 21-23 are similar to that of the data area bank 20. 
     All data area banks 20-23 may be simultaneously accessed by the addresses from the address area banks 12 and 13 to simultaneously read the 32-byte data. 
     In the above embodiment, the priority of the address area banks 12 and 13 and the priority of the data area banks 20-23 are separately determined. Alternatively, when the priority of the address area banks 12 and 13 is determined, the priority of the data area banks 20-23 may be taken into account so that the address area banks 12 and 13 are simultaneously activated only when different 8-bytes of data area banks of different access requesters are accessed. 
     In the above embodiment, there are two access requesters and the address area is divided into two banks (even-number block and odd-number block). However, the present invention is not limited to such an embodiment but m (m ≧ 2) requesters and an address area having n (n ≧2) banks may be used. 
     The access requesters or processors are not limited to IP&#39;s or IOP&#39;s. 
     In accordance with the present invention, the address area of the buffer storage is divided into a plurality of banks each of which is interleaved by blocks. Accordingly, even if the blocks specified by the addresses of a plurality of requesters are different, the plurality of address areas may be simultaneously accessed, and the competition between accesses in the bank storage address area can be reduced without increasing the hardware.