Frontiers of Supercomputing II "d0e7491"

Transfer Rate

Table 2 lists the peak MFLOPS rate for various machines, as well as the peak transfer rate (in megawords per second).

Recall that the operation we were doing requires three references and returns two operations. Hence, to run at good rates, we need a ratio of three to two. The CRAY Y-MP does not do badly in this respect. Each

Table 2. MFLOPS and Memory Bandwidth
Machine	Peak MFLOPS	Peak Transfer (megawatts/ second)	Ratio
Alliant FX/80	188	22	0.12
Ardent Titan-4	64	32	0.5
CONVEX C-210	50	25	0.5
CRAY-1	160	80	0.5
CRAY X-MP/4	940	1411	1.5
CRAY Y-MP/8	2667	4000	1.5
CRAY-2S	1951	970	0.5
CYBER 205	400	600	1.5
ETA-10G	644	966	1.5
Fujitsu VP-200	533	533	1.0
Fujitsu VP-400	1066	1066	1.0
Hitachi 820/80	3000	2000	0.67
IBM 3090/600-VF	798	400	0.5
NEC SX-2	1300	2000	1.5

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processor can transfer 50 million (64-bit) words per second; and the complete system, from memory into the registers, runs at four gigawords per second. But for many of the machines in the table, there is an imbalance between those two. One of the particularly bad cases is the Alliant FX/80, which has a peak rate of 188 MFLOPS but can transfer only 22 megawords from memory. It is going to be very hard to get peak performance there.