Tandy 1000 and 1000SX upgrades

Last Updated on January 24, 2023 by Dave Farquhar

I watched a YouTube video recently about a Tandy 1000sx and he inquired about what kind of upgrades he should try. So let’s explore some options for upgrading a Tandy 1000 SX, or the models it replaced, the Tandy 1000 and Tandy 1000A.

The Tandy 1000 and Tandy 1000SX have ISA expansion slots, giving them more options for upgrading than the IBM PCjr or the compact all-in-one Tandy 1000EX or HX. But the Tandy 1000SX with five slots can go a step further than the 1000 or 1000A, which only have three slots.

Considerations for Tandy 1000 and Tandy 1000SX upgrades

Picture of a Tandy 1000SX motherboard with more room for upgrades than the original Tandy 1000
The Tandy 1000SX has five slots, giving it more room for upgrades than a Tandy 1000 or Tandy 1000A had.

The 1000SX has five ISA expansion slots, so you’ll run out of IRQs before you run out of room to plug in expansion cards. You can plug in an XT IDE card, an I/O card, a network card, and still have two slots left.

An earlier Tandy 1000 or 1000A only has three ISA slots, so by the time you add an XT IDE card and a memory card, you have one slot left. There used to be a version of the XT IDE card that would let you piggyback a MicroRAM board so the combination only took a single slot, but I can’t locate them anymore. So by the time you add memory and storage to a 1000 or 1000A, you’ll have to decide whether an I/O card or a network card is more useful to you in the remaining slot. I’d go with the I/O card, but you have a better idea how you’re going to use the machine than I do.

Also, the 1000 and 1000A don’t have room for an 8087 math coprocessor. There were daughtercards to plug into an 8088 processor socket to give you room for an 8087, but as far as I know those have not been reproduced. So adding an 8087 to a Tandy 1000 or 1000A is probably more trouble than it’s worth.

So even though the Tandy 1000 and 1000A outwardly look a lot like a 1000SX, a fully loaded 1000SX has a fair bit more capability than an original 1000.


The first upgrade you absolutely want is an XT IDE-CF. This allows you to use a compact flash card as a hard drive.

You can get a 2 GB compact flash card for $10, but that doesn’t mean it’s the best match for an 8088-class machine like a Tandy 1000. But there’s a solution for that.

The BIOS on the card supports a drive that size. But keep in mind DOS versions prior to 3.31 were limited to 32 MB partitions. And if you do run a newer DOS version, that first write or directory listing induces a 25-second delay as the lumbering 8088 CPU calculates the free space. One workaround is limiting your C partition to 128 or even 32 megabytes to keep things tolerable.

Another solution is the utility FREESP written by a Canadian programmer and retro enthusiast who goes by Chartreuse. FREESP precalculates the free space using a faster method than the one built into DOS. You can run FREESP C in your autoexec.bat to reduce the delay to closer to 2 seconds and move it into your boot sequence. And if you can spare 1.2K of conventional RAM, you can use the terminate-and-stay-resident version, FREESPT, which intercepts the DOS routine, quickly performs the calculation, and populates the disk parameter block.

You can probably fit every title you would want to run on a Tandy 1000 on a 512 MB or 1 GB compact flash card.

Note that the original Tandy 1000 BIOS isn’t compatible with this card, so you will need to upgrade that model to the 1.01.00 BIOS. You can burn the replacement BIOS onto a pair of 28C256 EPROMs but unfortunately I don’t know where to get an image of the 1.01.00 BIOS.

More memory

This is the major point where the 1000 and the 1000SX diverge. You can install 2.6 megabytes of RAM in a 1000SX, though there’s not a lot of point in it. And the way you expand the two differs.

Tandy 1000SX memory upgrades

The 1000SX can be upgraded to 640K by adding 8 additional 4256 RAM chips. Remove jumper E1-E2 after you install the 8 additional chips.

And since the 1000SX has more expansion slots than you’re likely to know what to do with, you could put an EMS board in one of the additional slots. This board gives you 2 megabytes of expanded (EMS) memory, which was a trick for adding memory beyond 640K in 8088 based PCs. But if you’re using your 1000 as a games machine, there were no DOS games from its heyday that needed EMS. Of the 19 known titles that need EMS, all of them date from 1991 to 1994 and are more appropriate for a 386 or 486 machine. So I think EMS on a Tandy 1000SX is good more for bragging rights than for actual usefulness. You could use RAMDRIVE.SYS with the /A parameter to create a ramdisk out of some or all of that expanded memory. That’s what I would do if I had one.

Original Tandy 1000 and Tandy 1000A memory upgrades

The original 1000 needs a plug-in card for more RAM. The original Tandy board is rare and expensive so your best bet to get to 640K (and a bit beyond) is probably a MicroRAM board or a Lo Tech 1 MB board. The nice thing about these boards is you can also map some of their memory into upper memory, giving you UMBs if you run DOS 4.0 or later.

Network card

I recommend the Intel LAN adapter 8/16, because it works fine on an 8088 CPU like a stock Tandy 1000, and it’s still reasonably easy to find. You may need to run its configuration utility on a newer PC, and configure it for IRQ 9. This will make it use IRQ 2 on the Tandy 1000. You can then load a packet driver and the MTCP suite, which will then allow you to connect to FTP servers from the Tandy 1000, or have the Tandy 1000 operate as an FTP server so you can copy data to the Tandy 1000 from a newer machine over Ethernet.

This isn’t something you will use all the time, but I find it easier than messing around with removing the compact flash card, putting it into a modern system, and copying files. I find it easier to just boot the two machines and send the files to the vintage machine from a modern computer. This is the one thing I miss because I have a Tandy 1000 EX.

I/O card

This is more of a luxury, since not a lot of Tandy 1000 software used a mouse, but if you have some Tandy 1000 titles that did, having a mouse does help. Any 8-bit I/O card will work. The serial port is really what you want and need, but many I/O cards had a serial port, a parallel port, and sometimes a second serial port.

If the card has just a single port, you can stick with the default settings. If it has a printer port, you will need to change the printer port to IRQ5 and LPT2 to avoid conflicting with the built-in printer port on the motherboard. You won’t use this for much, but if you have a parallel port zip drive, you can connect it to that port and use a special version of the driver, Palmzip, and then you can use a zip drive to move software to and from your Tandy. Alternatively, if you prefer to use the original driver rather than paying for palm zip, the Iomega driver will work if you upgrade the CPU to an NEC V20. We’ll get back to the V20.

You can use an RS 232 serial mouse connected to one of the serial ports. I use the Cutemouse driver from the FreeDOS project, since it doesn’t use a lot of memory, but I find on my Tandy that it works better with Mouse Systems compatible mice better than Microsoft, unless I run DOS 6.22. Cheap serial mice with 3 buttons were Mouse Systems compatible, as was the so period-correct as to be over the top Logitech C7.


You can upgrade your Tandy 1000 a bit by installing a V20 CPU. It runs about 10% faster than an 8088 at the same clock speed, so some games will run a little bit nicer on a V20. And the V20 allows you to do things like use a Zip drive, with the native Iomega drivers. Or the very popular 3com 3c509 network card.

Like many things in retro computing, a V20 is a trade off. The V20 lets some software run that wouldn’t run otherwise, but at the expense of some degree of backward compatibility.

I do think a V20 helps more than it hurts. Software that doesn’t like the V20 is likely to also not like some of the  Tandy 1000’s other hardware quirks. Rumors of V20 compatibility problems persist, but the only confirmed compatibility issues I’ve seen are with the 8088 MPH demo for the IBM PC, which depends on the 8088 CPU, and early revisions of the IBM BIOS when used with an AST 6 Pack card. The Tandy 1000 uses a different BIOS and the AST 6 Pack is too large to fit in the Tandy 1000 case, so that problem won’t affect a 1000 either.

I haven’t tried this, but while we’re on the subject of CPUs, you can put a PC Sprint upgrade in an original Tandy 1000 to run it at 7.16 MHz. The 1000SX already runs at 7.16 MHz.

What about sound and VGA?

You could install a Soundblaster or an Ad Lib sound card and a VGA card compatible with 8-bit slots, but that point, you’ve just turned the Tandy 1000 into any other XT clone with sound and video that is really more appropriate for a 286 or 386 system. I would skip it and stick with the Tandy graphics and sound, personally. If I want OPL sound and VGA graphics, that era is much more enjoyable on a 386 or 486 system.

If I had an available slot, I could be persuaded to install an Adlib card or modern reproduction, since there were a few later titles that supported Tandy graphics but not Tandy sound, and you can install a sound card without losing Tandy sound. Installing a VGA card does come at the cost of Tandy graphics compatibility.

Second floppy drive

If your Tandy 1000 only came with a single floppy drive, installing a second floppy drive can be a nice upgrade. If you are adding a second drive, you might as well install a 3.5″ drive since some software did come on the 3.5″ disks. You can put a high density drive in these systems, but it will operate as a 720K drive. You will need to make sure the drive has a drive select jumper since the Tandy does not use the twist on the cable to determine drive A or B. If the drive you have doesn’t have a drive select jumper, keep in mind the default is DS1, so it will be your B: drive. Whichever drive you set to DS0 will be your A drive.

8087 co-processor

The 1000 SX has a socket for a math coprocessor. Not a lot of software uses it, and in some cases the co-processor being there introduces overhead that can actually slow the machine down very slightly. So I will leave it up to you whether you want to populate that socket, but if you are trying to max out your Tandy 1000 and that empty socket bothers you, an 8087-1 or -2 is the right chip to use, since either of those chips can run at 7.16 megahertz without issue. Remove the jumper at E3-E4 on the 1000SX mainboard after installing an 8087.

8087s used to be dirt cheap but demand has increased, so expect to pay $15 for one.

CGA monitor

Tandy CM-5 monitor
The Tandy CM-5 monitor was an entry level monitor at an entry level price, but its fuzzy .63mm dot pitch is offputting today.

The entry level Tandy CM-4 and CM-5 monitors match the Tandy 1000 styling, so they look good together, but their sharpness left a lot to be desired. Tandy used below-spec picture tubes in them with a dot pitch more appropriate for a television or a composite monitor. Those monitors are fine for games that use 320×200 resolution graphics modes. But for higher resolution graphics or text, they’re not optimal. If you plan to play Infocom games, you’ll tire of those monitors.

The Tandy CM-10 or CM-11 monitors were fine, if you can find one.

Most third party CGA monitors were comparable to the higher end Tandy monitors and give a nicer display than the CM-4 or CM-5. A Commodore 1084 is a popular choice because it works with a lot of other machines too, and has a speaker built in, but any PC CGA monitor from the 1980s will work.

You can also use a modern solution that converts CGA to VGA or DVI so you can use a more common VGA monitor, if you want a CRT tube, or a much more common (and modern) flat panel display. Although Tandy graphics had more colors than standard CGA in most modes, electrically the Tandy signal is completely compatible with standard CGA.

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