Data Transfers
Basic Data Transfers
   Basic
   Matched Memory
   Matched Memory w/o Wait
Streaming Data Transfers
   32 or 16 bit Streaming
   64-bit Streaming
   64-bit Streaming w/50ns Cycle

Basic Data Transfer Cycle
  The basic transfer cycle works by first defining the address (in memory or I/O space) where a transfer is to occur, and then, in a second operation of equal length actually transferring the data. Each half of the operation (defining the address and data transfer) takes 100ns, or 200ns total. 
   Five such “default” cycles can be performed in a millionth of a second. Each cycle moves four or two bytes per transfer, yielding a data transfer rate of 20MB/sec for 32-bit (4 byte) transfers or 10MB/s for 16-bit (2 byte) transfers.

Basic Data Transfer
Time
100ns
100ns
 
Addr
Data

Matched Memory Cycle
   MMC’s basic transfer cycle works by first defining the address (in memory or I/O space) where a transfer is to occur, inserting a wait state, and then actually transferring the data. Each third of the operation (defining the address, wait, and and data transfer) takes 62.5ns, or 187.5ns total. 
   Five and a third MM cycles can be completed in a millionth of a second. Each cycle moves four or two bytes per transfer, yielding a data transfer rate of 21.33MB/sec for 32-bit (4 byte) transfers or 10.66MB/sec for 16-bit (2 byte) transfers.

Matched Memory Cycle
Time
62.5ns
62.5ns
62.5ns
 
Addr
Wait
Data

MM cycle without Wait State
    Total cycle time is 125ns and for 32-bit transfers this results in a data transfer rate of 32MB/sec. Note that the 16MHz 8580 supports 62.5ns address and data transfer cycles. 

Matched Memory without Wait State
Time
62.5ns
62.5ns
 
Addr
Data



Streaming-Data Transfers
   In Sep 1989, IBM announced three new procedures for higher data transfer rates- 40MB/s, 80MB/s, and 160MB/s. The 80MB/sec streaming-data rate can be obtained with existing hardware (as of 1991!). Streaming data is only effective for applications that transfer large amounts of sequentially arranged data.
   The actual data transfer rate achieved is a function of the total burst (packet) length, where the overhead (arbitration process and the address designation of the burst) is “amortized” over a large amount of data. Applications that can benefit include high speed LAN adapters (FDDI), storage devices (SCSI adapters, DASD), and channel-attached memory (memory cards).
   NOTE: 80 and 160MB/sec streaming is only available on machines / adapters that have dual-path bus capabilities. Both adapters / devices must support streaming.

32-bit or 16-bit Streaming
   This is a refinement of the basic cycle. The data transfer is still preceeded by the address, but the address is designated at the beginning of the transfer and incremented based on the number of bytes of information to be transferred.
   This reduces the cycle time to 100ns and results in an instantaneous data rate of 40MB/sec for 32-bit transfers and 20MB/sec for 16-bit transfers for sequentially ordered data. Note the Address bus has nothing to do after the initial address. The 40MB/sec rate is available on single path systems.

32 or 16 Bit Streaming
Time
100ns
100ns
100ns
100ns
 
Addr
     
   
Data
Data
Data

64-bit Streaming
   The address bus is used at the start of the data transfer for the address but then is used to transfer data, resulting in a 64-bit data path. Transfer rates of 80MB/s can be achieved for sequentially ordered data. The 80MB/s data rate should be attainable with existing hardware. Note that a dual-path system is required. On the 90 and 95 models, the Type 3 and 4 complexes have the enhanced dual path memory buses.

64-Bit Streaming
Time
100ns
100ns
100ns
100ns
 
Addr
Data
Data
Data
   
Data
Data
Data

64-bit Streaming with 50ns cycle
   The address bus is used at the start of the data transfer for the address but then is used to transfer data, resulting in a 64-bit data path. The cycle time has been reduced to 50ns. There is only a 64-bit form of this transfer.
   It can support 160MB/sec for sequentially ordered data. The 160MB/sec may require new signal drivers and recievers. (The Streaming-capable adapters may have it already, like the Fast/Wide, FDDI, FW RAID..). A dual-path system is required.

64-Bit Streaming with 50ns Cycle
Time
50ns
50ns
50ns
50ns
 
Addr
Data
Data
Data
   
Data
Data
Data

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