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I do not understand why there's an ISA memory card. The 80286 can only address 16MB of RAM. Why not just fill the memory map as standard, then there's no need
by lproven 2y ago
I do not understand why there's an ISA memory card.
The 80286 can only address 16MB of RAM. Why not just fill the memory map as standard, then there's no need for SIMM slots or any other memory expansion?
Give me a few Upper Memory Blocks for DOS, and provision for 32MB of EMS as well, and frankly for a DOS machine there is nothing left to add in terms of memory.
How much is 48 _megabytes_ of RAM in 2024? 5¢? 10¢?
- NikkiA 2y agoI bought 16MB of SRAM for a Z80 project a few weeks back, they were £3/4MB(32Mb) chip
- lproven 2y agoThanks for that! More than I thought, but still, a relatively small amount for what will work out as a quite expensive retro build.
- rasz 2y ago>How much is 48 _megabytes_ of RAM in 2024? 5¢? 10¢? about $500-1000 https://eu.mouser.com/c/semiconductors/memory-ics/sram/?memory%20size=114%20Mbit~~1%20Gbit&rp=semiconductors%2Fmemory-ics%2Fsram%7C~Memory%20Size https://eu.mouser.com/c/semiconductors/memory-ics/sram/?memo... >Why not just he said the magic words!
- moosedev 2y agoThose are SRAMs. A 286 system wants DRAM, which is usually a lot cheaper. https://www.geeksforgeeks.org/difference-between-sram-and-dram/ https://www.geeksforgeeks.org/difference-between-sram-and-dr...
- rasz 2y ago286 doesnt want anything, CPU is ram agnostic. Project author didnt want to mess with implementing DRAM controller, not that its difficult. Here a simple 16 bit controller realized with ten 74xx chips https://amigaprj.blogspot.com/2013/05/amiga-fast-ram-expander-with-simm.html https://amigaprj.blogspot.com/2013/05/amiga-fast-ram-expande...
- moosedev 2y agoOh right, I didn’t read far enough to see there’s no DRAM support - very unusual for a 286 system (at least a PC-compatible one). That’s a big tradeoff, indeed. Thanks!
- rasz 2y agoI wouldnt call it a tradeoff. Author didnt want to design memory controller, and SRAM gets him effortless 0 wait state access. Personally Im also a fan of keeping ram oldschool. I even reverse engineered a ram card for a 386 board just last week https://github.com/raszpl/386RC-16 https://github.com/raszpl/386RC-16
- moosedev 2y agoThe tradeoff would be speed and implementation simplicity against the high cost of SRAM, like you highlighted :) (Re your 386 RAM board: Nice necroproject!)
- lproven 2y agoAh, OK, it is all static RAM? Ouch...
- NikkiA 2y ago> about $500-1000 https://eu.mouser.com/c/semiconductors/memory-ics/sram/?memo https://eu.mouser.com/c/semiconductors/memory-ics/sram/?memo... Only because you're including RAM spec'ed at 75pS access times. If you limit the selection to 133MHz (the slowest 'max speed' - ridiculous, you can still easily purchase NEW 50nS and 70nS SRAM elsewhere, this is why I don't buy from mouser)... Then the price falls to £5 for a 32MB (256Mbit) chip, which isn't excessively priced, but it still more than I paid for similar chips a few weeks ago.
- rasz 2y agoThats a serial Pseudo SRAM you are looking at :)