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Old 26 August 2018, 13:30   #216
plasmab
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Quote:
Up to at least 1984 there were no fast page mode, only page mode. Fast memories had a minimum cycle time of about 230ns with full RAS/CAS, down to about 120ns in page mode (there were however at least one chip with an 100ns page mode timing in 1984).
Most of the DRAM was much slower.
This is wrong (EDIT: Or at least partially wrong.. see below). Ram timings arent quoted in FPM times. How could they be before FPM was invented. Its a part of the random access time. The BBC used 100ns ram before 1984.

Quote:
Originally Posted by roondar View Post
But now I think I do. What's happening is that these systems don't use page mode. They use random-access mode. And memory used for random access is much slower than it's rated (page mode) speed.
I thought that was well known. AFAIK only Jens cards use Fast Page mode (on the amiga... maybe he's using the EDO variety). The TF328 doesnt even use it. Fast page mode is when you read a burst out and you can do that without starting the whole cycle again.

The headline RAM numbers are for random access. Not FPM or EDO.

Quote:
Just check the datasheets: the KM4164B-10 used in the BBC Micro has a random access cycle of 190ns. That's a lot closer to the actual memory access speed of the system than 100ns is. Similarly, for the 41256-15 commonly used in the early Amigas the random access cycle is 260ns. That is really close to the 280ns the system accesses memory at.
Maybe then the RAM speeds are quoted in RAS to CAS times...

EDIT: Haynie wanted to use it on something A3000 related but he got told not to for reliability or something. I forget the exact reason.

Last edited by plasmab; 26 August 2018 at 13:38.
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