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More than 640K in an IBM PC

Great Hierophant

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I recently acquired an Everex Systems EV-138 Memory Board. I am going to try to use it to boost my system to more than 640K of RAM. It has three banks, 2 with 64kx1 modules, 1 with 256Kx1 module. What I will do is to remove one of the 64Kx1 modules and replace the other 64Kx1 with a 256Kx1 module. With some fiddling of the motherboard's switches and the Everex's jumpers, it should work.
 

Anonymous Coward

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It's possible...but I wouldn't count on it. Depending on which graphics display adapter you are using, most of the free UMBs will reside in the D and E regions. Installed in a 256k motherboard, you'll only make it up to the C region. Assuming you can actually get a UMB manager working at most you'd free up 32kb. If you really want to do something like this, I recommend a LIM 4.0 EMS board and a copy of QRAM 2.0.
 

gerrydoire

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It's possible...but I wouldn't count on it. Depending on which graphics display adapter you are using, most of the free UMBs will reside in the D and E regions. Installed in a 256k motherboard, you'll only make it up to the C region. Assuming you can actually get a UMB manager working at most you'd free up 32kb. If you really want to do something like this, I recommend a LIM 4.0 EMS board and a copy of QRAM 2.0.

What benefit would more than 640k do in a computer that runs at 4.77 mhz?

My QRAM Card has more than 640k, but I've never used that feature.
 

Trixter

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What benefit would more than 640k do in a computer that runs at 4.77 mhz?

Disk cache and loading TSRs out of the 640K memory area are the obvious benefits. I wish I could program my hobby projects on a 768K machine because they're getting big enough that I run out of memory in my programming IDE.
 

per

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Disk cache and loading TSRs out of the 640K memory area are the obvious benefits. I wish I could program my hobby projects on a 768K machine because they're getting big enough that I run out of memory in my programming IDE.

Can't somebody make a card that got RAM adressable above 640K? I know 4164/41256 are Dynamic RAM and require some extra logic to work, but aren't the Static RAMs getting quite fast therse times?

Static RAM doesn't really require to much additional logic, only some logic that trigers Chip-enable when it's addres range is selected. A single TTL chip can do that job correctly.
 

vwestlife

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The 5150's motherboard DIP switches limit the maximum addressable RAM to 640K (or even 544K on early BIOS versions) regardless of how much extra RAM you physically put in. Special software driver programs may be able to get around this. With CGA, the total addressable "conventional" RAM would be 736K.
 

per

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The 5150's motherboard DIP switches limit the maximum addressable RAM to 640K (or even 544K on early BIOS versions) regardless of how much extra RAM you physically put in. Special software driver programs may be able to get around this. With CGA, the total addressable "conventional" RAM would be 736K.

By hardware, all the DIP switches do is to determine what of the four banks of RAM IC's on the motherboard that's enabled on certain addresses.
By software, the switches can be read and examined.

The switch setting does not have anything to do with how much memory in the system. There is usually no way software can read switches on RAM expansion cards.

The BIOS will only count the first 640Kb anyways, because it is programmed to do so, but it can easly be modified to count higher if you got an EPROM burner for the spesiffic EPROM type.

I don't think DOS cares what the BIOS count to, however, I'm not sure.
 

Chuck(G)

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There were some PCs with more than 640K base RAM. One that comes to mind is one of the Visual boxes (maybe the Commuter)? Something like 918K.

I don't see why the "hole" between D0000-F0000 couldn't be filled with expansion RAM and used for buffers, cache, TSRs, etc., given the right memory card.
 

per

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There were some PCs with more than 640K base RAM. One that comes to mind is one of the Visual boxes (maybe the Commuter)? Something like 918K.

I don't see why the "hole" between D0000-F0000 couldn't be filled with expansion RAM and used for buffers, cache, TSRs, etc., given the right memory card.

You can also put an EEPROM somewhere in there and use it as permanent data storage :D , but you'll rather want to put that into the BIOS extension area (with a dummy BIOS Extension header of course!)
 

Anonymous Coward

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If you search the internet, there are instructions to install 1mb on the XT planar and access up to 896k by reprogramming a ROM to rearrange the reserved regions about 640k. If you want to be able to use memory above 640k as conventional, it must be contigious. Non-contigious memory can still be made available, but only to load drivers.

An easy way to get 736k conventional on an XT is to use the TSR provided with PC DOS 2000. If you have a VGA card, this allows you to turn off the graphical features and get access to 736k. However, this makes use of memory on the graphics adapter itself, which is said to be several times slower than main memory. If you use this trick in conjunction with LIM 4.0 board using QRAM, you can make the 896k available with 736k acting as conventional memory.
 

vwestlife

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Many later Tandy 1000s (including my 1000RL) allow for up to 768K to be installed on the motherboard, but only up to 640K is addressable to DOS. The memory above 640K is permanently reserved for use as video RAM, even when the video is not using all of that extra 128K.

On the other hand, my Ampro "Little Board/PC" provides three 256K SIMM sockets, and with the full 768K RAM installed, it does provide extra DOS-accessible RAM above 640K: up to 704K when you have its video controller in MDA mode, or up to 736K when it is in double-scan CGA mode (text mode resolution increased to 640x400 on an EGA-spec monitor, plus standard 320x200 and 640x200 graphics modes). It has a NEC V40 CPU at 7.16 MHz, intergrated serial, parallel, floppy, and SCSI hard drive controllers, and one 8-bit ISA slot. It has a socket for a proprietary NEC V-series math co-processor (not pin-compatible with the 8087) which was ultimately never released by NEC. It has a semi-high density floppy controller: it supports 1.2MB 5¼" drives, but only 720K 3½" drives, since the 1.44MB format hadn't been invented yet when it was introduced.

The Ampro is also the only PC I've seen with a functioning "System Request" key implemented in BIOS: pressing the SysReq key on your keyboard (a.k.a. Alt-Print Screen) at any time pops up its hardware configuration screen.
 

vwestlife

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OMG, you have an Ampro LB/PC? Do you have the software for it? Could I beg a copy?
Yes, I have the original 5¼" disks buried somewhere in my collection. I'm actually about to begin retrieving data from all my old 5¼" PC disks and copying it to CD-R for safe storage, so I guess I'll add the Ampro disks to the list.
 

Trixter

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An easy way to get 736k conventional on an XT is to use the TSR provided with PC DOS 2000. If you have a VGA card, this allows you to turn off the graphical features and get access to 736k. However, this makes use of memory on the graphics adapter itself, which is said to be several times slower than main memory. If you use this trick in conjunction with LIM 4.0 board using QRAM, you can make the 896k available with 736k acting as conventional memory.

I only have CGA, and losing graphics just to gain 12K of RAM doesn't sit well with me :)

All of this goes away with a 386 and a memory manager. I remember using 386max and "turning off" graphics with a VGA card to get nearly 896KB conventional DOS ram.
 

vwestlife

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I only have CGA, and losing graphics just to gain 12K of RAM doesn't sit well with me :)
On that CGA system, installing a Hercules monochrome graphics card and using UMBHERC.SYS from PC DOS 6.1 or higher would give you 60K of UMB space for loading drivers and TSRs -- and you'd still be able to use the Hercules card in MDA text mode on a monochrome display. Or at least that's how it's supposed to work; it's been years since I had a Hercules-compatible card.
 
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