Epson created the first “true laptop computer” with the HX-20. It was released in July 1982 and weighed 1.6 Kg. The successor to the HX-20 was in 1984 the 2.3 Kg PX-8 which was now capable to run CP/M due to its Z80-compatible CPU. The next model, the 1985 PX-4 combined features from the PX-8 and the HX-20, was also Z80-based and offered CP/M. I could not find the weight of the PX-4, but it was probably in the range of the HX-20.
The HX-20, the PX-8, and the PX-4 were all laptop computers, i.e. they required a desk or at least a lap to sit on so you can use it with your hands. But there are usage scenarios that require a more mobile device, i.e. one that you can hold in one hand while the other one uses the device. It is technically possible to use e.g. a HX-20 for this purpose, but it’s not comfortable at all.
So if you are a device manufacturer like Epson and want to serve the market that needs that higher mobility, what do you do? You design a version of the PX-4 that is lighter and that you can hold in one hand. Voila the Epson Handy Terminal (EHT)-10 family from 1986 onwards.
The (original?) model, the EHT-10 is a (from a today’s point of view) massive beige brick with an on/off switch at the top and an enormous 7-inch black-and-white display. It is mainly a touchscreen that you use with your finger, no pen required.
The basic usage scenario of the EHT-10s is mobile data entry. But you do not need to develop your application on the EHT-10, in fact, you can’t. You develop it instead on a desktop CP/M machine, and then simply transfer it to the EHT-10. To that end the EHT-10s are equipped with both CP/M 2.2 and the basic runtime environment that allows to run Epson Basic programs (e.g. coming from a PX-4). All you have to take into account are the different display sizes and input possibilities. This does not mean that you can get a CP/M shell on the EHT-10 or an editor to enter Basic programs; the EHT-10 is purely an execution device. You can transfer your programs to an EHT-10 either by serial connection, or by “IC Card”, or burn it on an EPROM and stick it into the conveniently located socket next to the main battery. So, you cannot program on the EHT-10, but you can connect the EHT-10 to your development computer by using a “Development Cartridge” for debugging purposes.
The main battery of the device is a proprietary 4.8V, 700 mAh NiCd module which gives the device a runtime of 8h. In case you have to change the battery, there is a secondary RAM backup battery (4.8V, 45 mAh). Using the stock power supply it takes 10h to load the main battery and a whopping 45h to load the secondary one it was completely empty.
On the sides of the case, at the bottom, there are two massive buttons to which you could strap a ribbon, so the device could go around your neck, thus freeing also the other hand if needed.
The other two models of the family are, first, the EHT-10/2b which looks like an oversized calculator with its 4-line display and its 34 keys (there is even a CALC key which puts the device in basic calculator mode). Apart from that, it’s innards are the same as the EHT-10’s.
The second model is the EHT-10/2 which is a EHT-10/2b without a backlight.
I received my two EHT-10/2bs (plus a printer) together with a simple 5.6V, 0.4A travel power adapter with a connector crudely welded to it. I have a 64 kB and a 128 kB RAM model. Using this power adapter I could never get the 128 kB model to run for more than a few seconds even connected to the power adapter, but the 64 kB model worked fine. And if you think about it, this makes complete sense. There was no main battery in any model (because they would be quite proprietary NiCd modules), but the backup cells were still in there. No, if you load the backup cells, the (battery-buffered) RAM immediately run on the cells, and even if they are full, the power needed by 128 kB is seemingly larger what the backup battery can deliver when switched on. The 64 kB model need less power and can run on my power adapter. The stock adapter had 6.0V anyway.
Epson produces many printers, and there is a clip-on dot-matrix printer model that fits the top of any EHT-10 device (it even uses a tiny ribbon cassette which you find even today on ebay).
There are almost no Internet sources on the EHT-10. The only one is listed below. It contains some photos (actually showing the very devices I ended up with), some (but unfortunately not all) manuals and the development software meant for CP/M or MSDOS desktops.
Epson sold these devices from 1986, but they were not the first company to target the ultra-mobile market. The first company probably was DVW (later on Husky Computers) with their Husky line of devices from 1981. The competition to the EHT-10 at the time was probably the 1984 Husk Hunter 2 which weighed 1.15 Kg, and had to be held in landscape mode, where as the EHT-10 was below 1 Kg, 50% smaller, and could be used hanging from the neck. The CPU and OS on both the EHT-10 and the Husky Hunter 2 was very similar.
Another competitor would have been the much lighter and cheaper Psion Organizer II from 1986, but it was much more proprietary in terms of CPU and OS, had much less RAM, and was much slower than the EHT-10.
Progress cannot be stopped and Epson later on gave up the EHT-10 family for the 1991 EHT-20, EHT-30, and EHT-40, which were PC- and DOS-based devices for the same usage scenario (all looking quite similar to the original EHT-10). The final model was the 1995 EHT-400c which was a small color-screen pen-based Pen Windows 3.1 tablet.
Epson EHT devices are probably quite scarce today because they were probably never distributed over normal computer stores (but to system integrators) and they were very pricey (which they could be in the beginning because there was not much competition). As a piece of industrial equipment, though, only a few people are interested in them.
Models
EHT-10
- CPU: Z80@3.68 MHz (CMOS)
- RAM: 64-256 kB
- ROM: 128 kB System ROM, up to 128 kB Application ROM
- OS: CP/M 2.2
- Batteries: main: backup: NiCd cells
- Interfaces: RS232C, Barcode Scanner, IC cards
- Dimensions: 21.3 x 9.3 x 3.8cm
- Weight: 600g without main battery
- Display: 12 x 14 characters (5 x 14 characters out of which can be used as a touch screen), 84*154 pixels
EHT-10/2
- same data as the EHT-10/2b, but without the backlight
EHT-10/2b
- same data as above except the
- Display: 20 x 4 characters, 120 x 32 pixels, with backlight
- Keyboard: 34-key-calculator keyboard
Rare & Old Computers 