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- From: dwilliam@jabba.ess.harris.com (David Williams)
- Subject: Cached DRAM from Mitsubishi
- Message-ID: <1992Jul29.214908.7876@trantor.harris-atd.com>
- Keywords: yow!
- Sender: news@trantor.harris-atd.com (News stuff)
- Organization: Harris Information Systems Division, Melbourne, FL
- Date: Wed, 29 Jul 1992 21:49:08 GMT
- Lines: 38
-
- I was flipping through the May issue of Electronic Design, and an
- ad from Mitsubishi caught my eye. They have a DRAM chip now available
- with built-in cache. This looks interesting - a 1M by 4 DRAM with a
- built-in 4K by 4 SRAM cache. Apparently, the chip has an internal bus
- that lets the SRAM cache do a line copy to/from the DRAM portion at
- 64 bits. (16 x 4bit internal bus) Speed is claimed to be 10ns when a
- cache hit occurs, 70ns in case of a miss (actually, a miss causes a
- 280ns DRAM cycle, but the SRAM can start doing stuff again in 70ns while
- the DRAM is busy)
-
- The reason I bring this up is the recent discussion about high-bandwidth
- main memory systems. At 10ns, this critter has a seriously fast
- cycle time. For a minimum system, you'd use 8 of them to get a 8M x 32bit
- memory array, which gives you a 32K x 32bit (128K x 8) cache. What kind
- of performace could we really expect from this configuration? Aren't most
- secondary caches quite a bit larger than this? I guess I need to go do
- some simulation.
-
- I guess the performance is really going to depend on the hit rate of
- the cache, but this thing looks like an excellent candidate for burst mode
- access. If no miss, the cycle can be 2-1-1-1, and if a miss, we have to
- add 60ns for the first access (4-1-1-1 ?) since the DRAM has to load the
- cache line to the SRAM inside the chip. An aside - with 8 chips, this
- is the equivalent of a 512-bit load from main memory to cache in 70ns,
- since each chip loads 64 bits internally.
-
- Anyone have any more information on this type of device?
-
-
- Dave Williams My
- dwilliam@jabba.ess.harris.com opinions
- "Huh? What? Could you repeat the question?" only.
-
- --
- Dave Williams My
- dwilliam@jabba.ess.harris.com opinions
- "Huh? What? Could you repeat the question?" only.
-
-