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Hyundai Super 16 XT machine - more than 512kB RAM possible?

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First post, by smoke86

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Hi,
I recently finished putting back to life my first ever XT desktop system, although I had to build my own case for it.
It is based on Hyundai Super 16 board, which - according to retroweb - only has 4,77 MHz bus and 512 kB of RAM.
I was wondering if it is possible to make it a little bit faster - I already put NEC V20 CPU and 8087 FPU in it, but I 'd really like to give it at least 640kB RAM total (mayba a RAM addon card?).
I understand that turbo mode is probably out of question - maybe swapping clock crystal (which will overclock ISA bus as well) is a way to go?

Current setup is:
- Hyundai Super 16 motherboard https://theretroweb.com/motherboards/s/hyundai-super-16
- NEC V20 (swapped from AMD 8088)
- Intel 8087 FPU
- VGA Paradise video card (MDA and CGA cards as spares)
- ESS Es488 audio card
- 20MB MFM HDD (XT-CF card as spare)
- 1,44 MB FDD drive acting as 720kB drive
- MS-DOS 3.30a

I'm looking for a way to give irt at least more RAM, some games like Prince Of Persia in VGA and Adlib mode are quite demanding.

Reply 1 of 7, by Babasha

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PicoMEM? I think is most advanced and not so expensive solution or you can search for authentic ISA8 RAM card but they are rare.

Need help? Begin with photo and model of your hardware 😉

Reply 2 of 7, by Jo22

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Hi, I think there once were 512KB to 640KB RAM cards.
They were part of certain PC/XT multi i/o cards with Real-Time Clock etc.

Then there are modern solutions, such as the Lo-tech 1MB RAM Board or the "microRAM" card (Monotech).
The latter is a daughtercard for the XT-IDE Deluxe card but it can be used stand-alone, too.

Then there's the aforementioned PicoMEM card, but I have little experience with it.

The modern altternatives have the advantage that they can be used to create upper memory (UMBs).
By using USE!UMBS.SYS it's possible to make DOS see these blocks as available.

"Time, it seems, doesn't flow. For some it's fast, for some it's slow.
In what to one race is no time at all, another race can rise and fall..." - The Minstrel

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Reply 3 of 7, by wierd_w

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lotech 1mb RAM card has user selectable DIP switches which let you turn certain banks on and off.

Has a bonus feature of being able to put ram in the UMB area, that HIRAM/USE!UMBS can turn on, which is useful on an XT.

Reply 4 of 7, by Many Bothans

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Interested to know what you did for the case? The side keyboard connector is unusual, even for a time before industry standards.

Reply 5 of 7, by smoke86

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So, the solution regarding RAM is a RAM card, but mind the fact that 8088 can handle only 1 MB of RAM and I only actually need extra 128 kB. Real question is, can the BIOS handle more than 512k, as the machine is designed to have 512k max.
About the case, I actually made it from scratch using furniture construction boards. I decided to have keyboard connector at the front of a case and ISA cards at the side - see photos attached.

Reply 7 of 7, by wierd_w

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The main sources of limitations for an XT, conserning base system memory, are as follows:

XT class machines can address a maximum of 1mb of address space.

The system memory portion must be all one big piece (contiguous)

Any ROM starting before the end of the 640k area will prohibit reaching the full 640k size, as a result.

This includes various video devices, which usually park themselves *just* outside the 640k area, but can 'start sooner' on certain 'not fully XT compatible' systems.

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