3 ms·

>72pin simm in 1988 Afaik other companies picked up 32bit simms very slowly. SUN in 1991 in SPARCstation IPX. First x86 support showing up in 1992 on 486 board

by rasz 4y ago

>72pin simm in 1988 Afaik other companies picked up 32bit simms very slowly. SUN in 1991 in SPARCstation IPX. First x86 support showing up in 1992 on 486 boards just before introduction of VLB slots. Apple was year later with LC III/520 and Centris in 1993.

hakfoo 4y ago
I have a 386SX that has a single 72-pin SIMM socket. It xseems to be a 1991 design by the stickers on components. Even more weirdly, the machine could be equipped with a 286 daughterboard instead of the 386SX. I wonder if it just discarded half of each memory access to fill the 16-bit bus.
- rasz 4y ago
  brand/model? There was also Compaq DeskPro 386/20N, came out in ~December 1991 https://books.google.com.au/books?id=KT0EAAAAMBAJ&pg=PA106&lpg=PA106 https://books.google.com.au/books?id=KT0EAAAAMBAJ&pg=PA106&l...
  - hakfoo 4y ago
    Magnavox Headstart/SX. Here's the mainboard diagram http://www.uncreativelabs.de/th99/m/P-R/34385.htm http://www.uncreativelabs.de/th99/m/P-R/34385.htm (although they claim it's 20MHz, the one I have is 16) It's strangely overbuilt-- very feature rich BIOS, almost tool-less chassis, 72 pin memory socket, lots of surface mount parts, but paired with the slowest 386 on the market and a hard disc that was probably about 3 years out of date (Seagate ST351A/X-- capable of running in that weird 8-bit IDE mode) I have to figure it was Philips flexing their last few years of being a premium electronics manufacturer-- they can make a nice PCB and chassis but still have to buy the computery stuff from elsewhere.
    - rasz 4y ago
      Indeed appears to be middle of 1991 design. Nice!
lproven 4y ago
Sure, yes, because the purpose of 72-pin SIMMs was for 32-bit wide memory access. Before 72-pin SIMMs were 30-pin SIMMs. Simple arithmetic shows you that you can't route a 32-bit memory bus over 30 pins. You need banks of SIMMs and that means they need to be matched. But the 386DX was too expensive, because it needed a 32-bit memory bus. So it didn't sell well and was mainly used in PCs used as servers. PC servers didn't really exist yet in 1985. That's why the 386SX was invented, with a 16-bit memory bus. It meant the motherboard only needed a 16-bit memory bus, meaning it was much cheaper. But that means it doesn't really need 72-pin RAM. It wasn't until the 486 (and 68040) went mainstream that ordinary desktop computers needed 32-bit memory buses and therefore 72-pin RAM, but over time, economies of scale drove down the cost of 72-pin RAM so it became cheaper and gradually got adopted, and the 16-bit-bus 386SX (and derivative chips with the 486 instruction set, such as the 486SL and 486SLC) gradually went away.
- rvense 4y ago
  68020 and 68030 were fully 32 bit, wasn't it? They had the dynamic sizing thing so they could boot of one EPROM, but they had the full bus expose AFAIK.

by rasz 4y ago

hakfoo 4y ago

I have a 386SX that has a single 72-pin SIMM socket. It xseems to be a 1991 design by the stickers on components. Even more weirdly, the machine could be equipped with a 286 daughterboard instead of the 386SX. I wonder if it just discarded half of each memory access to fill the 16-bit bus.

rasz 4y ago
brand/model? There was also Compaq DeskPro 386/20N, came out in ~December 1991 https://books.google.com.au/books?id=KT0EAAAAMBAJ&pg=PA106&lpg=PA106 https://books.google.com.au/books?id=KT0EAAAAMBAJ&pg=PA106&l...
- hakfoo 4y ago
  Magnavox Headstart/SX. Here's the mainboard diagram http://www.uncreativelabs.de/th99/m/P-R/34385.htm http://www.uncreativelabs.de/th99/m/P-R/34385.htm (although they claim it's 20MHz, the one I have is 16) It's strangely overbuilt-- very feature rich BIOS, almost tool-less chassis, 72 pin memory socket, lots of surface mount parts, but paired with the slowest 386 on the market and a hard disc that was probably about 3 years out of date (Seagate ST351A/X-- capable of running in that weird 8-bit IDE mode) I have to figure it was Philips flexing their last few years of being a premium electronics manufacturer-- they can make a nice PCB and chassis but still have to buy the computery stuff from elsewhere.
  - rasz 4y ago
    Indeed appears to be middle of 1991 design. Nice!

lproven 4y ago

Sure, yes, because the purpose of 72-pin SIMMs was for 32-bit wide memory access. Before 72-pin SIMMs were 30-pin SIMMs. Simple arithmetic shows you that you can't route a 32-bit memory bus over 30 pins. You need banks of SIMMs and that means they need to be matched. But the 386DX was too expensive, because it needed a 32-bit memory bus. So it didn't sell well and was mainly used in PCs used as servers. PC servers didn't really exist yet in 1985. That's why the 386SX was invented, with a 16-bit memory bus. It meant the motherboard only needed a 16-bit memory bus, meaning it was much cheaper. But that means it doesn't really need 72-pin RAM. It wasn't until the 486 (and 68040) went mainstream that ordinary desktop computers needed 32-bit memory buses and therefore 72-pin RAM, but over time, economies of scale drove down the cost of 72-pin RAM so it became cheaper and gradually got adopted, and the 16-bit-bus 386SX (and derivative chips with the 486 instruction set, such as the 486SL and 486SLC) gradually went away.

rvense 4y ago
68020 and 68030 were fully 32 bit, wasn't it? They had the dynamic sizing thing so they could boot of one EPROM, but they had the full bus expose AFAIK.