HP Palmtop 95LX - Technical information
Contents of this page:
The HP 95LX was the first MS-DOS-based palmtop PC by Hewlett Packard and
has been introduced in April 1991. Project name at HP was
The 95LX has MS-DOS 3.3 in ROM, along with powerful PIM applications.
Hardware is based on a NEC V20 CPU (CMOS version) running at 5.37 MHz.
There are 512kB and 1MB RAM models available,
graphics adapter is an MDA, not CGA as the newer HP Palmtops have,
with 16 x 40 characters and 128 x 240 pixels.
The pictures show the mainboard of a 95LX with 512 kB RAM. The IC
with "© 1990-HP" is the ROM, you can also see
the NEC V20 CPU, the Intel chip which probably includes bus controller etc.,
and the RAM chip next to the ROM. Note that there is room for one more RAM chip,
please see next section for info about a memory upgrade!
The next picture shows the memory configuration of the 1 MB version of the 95LX:
If your 95LX doesn´t say "1 MB" in the upper right corner of the screen
edge, it is a 512kB unit or it has been upgraded to 1MB RAM by a third party.
In order to definitely know how much RAM it really has, either open it
and look for the RAM chips (compare to the pictures above), or go into
Filer, press Menu, Dos (or System, language dependent) and execute the command chkdsk.
If the total amount of disk space (which includes the ROM contents!) is reported as
922624 bytes, you have a 1MB unit. If it is reported as 777216 bytes,
you have 512 kB.
There is only one upgrade which can be applied to a 95LX with 512kB:
You can solder in another 512kB RAM chip to upgrade the unit to
1 MB of RAM.
The required RAM chip should cost not more than 10-15 US$. Since this is a quite old kind of RAM chips, it may be hard to get such a RAM chip.
Arne Christensen described how to do it.
Read his instructions here!
Arne writes that you do not need to move the ROM chip from the middle
to the top position, but that you can solder the new RAM chip at the top
position, which is not the factory-default for 1MB 95LXs (see pictures above).
There is no backlight upgrade available for the 95LX.
It may be possible to adapt the backlight upgrade
for the 100LX / 200LX / 1000CX to work with the 95LX, but
nobody has done this yet.
Please report, if you did it!
Storage cards (SRAM, ATA flash, Compact Flash)
Actually, the 95LX was designed to work only with SRAM cards for storage,
these cards are available in capacities up to 4 MB (or are there even 8MB SRAM cards?),
and they are fairly expensive. The 95LX can handle
up to 2 MB without any problem, for larger SRAM cards,
you may need the
SRAM cards need a battery to keep their data,
some cards use a lithium coin battery, some have an internal rechargeable
battery, which is charged by the device they are used in.
The PCMCIA interface of the 95LX follows the standard PCMCIA 1.0
(don´t confuse that with the PCMCIA type, the slot of the 95LX
is PCMCIA type II, i.e. you can use cards with a thickness of 3,3mm or 5mm),
thus it is designed to work only with "memory mode" PCMCIA cards.
No "device mode" cards, such as modems or many flash cards, are recognized
(There is one exception: NewMedia designed a PCMCIA modem for the 95LX).
SRAM cards are memory-mode cards, but Flash cards, no matter if full-size ATA cards or
Compact Flash cards, are generally device mode cards, but some better ones
can also be used in memory mode, and those are the cards which work in the 95LX.
However, these cards require a special
The highest capacity the 95LX can handle is 32MB, since the MS-DOS 3.3 in
ROM only handles partitions up to 32MB.
The original "Sundrv" driver is made by Sundisk (which is now Sandisk), and thus only
works with Sandisk or Sundisk flash cards. The link above also points to a modified version
of that driver, which doesn't check for the card manufacturer anymore,
so it will also work with other cards, but still only with cards which
support that memory mode, of course.
There is one more problem with using flash cards in the 95LX: SRAM cards always need
a power supply to keep their data, and as long as they are inserted into the 95LX,
they get their power from the palmtop, so the battery of the card lasts longer.
So the 95LX is designed to always supply power to the card which is inserted,
no matter which type of card. Thus it permanently supplies power to flash cards, too.
cards need way much more power from the 95LX than
SRAM cards, and the 95LX, thinking it is an SRAM card which needs the power,
supplies power even during it is switched off.
Leaving the 95LX switched off with a flash card inserted will deplete
the batteries within days or even hours! So always pull out the flash card if
you don´t use the 95LX!
Christian Felique tried a hardware hack to solve this problem, and it was successful. He writes:
The PCMCIA interface has three voltage lines: Vcc, Vpp1 and Vpp2.
Vcc is always powered, Vpp only when reading from or writing to the memory card.
If you cut the Vcc line, the power problem with Flahs cards is solved. However,
it may be that you cannot use SRAM cards anymore.
Another problem with Flash cards is that they need much power for read/write operations,
which can make the screen flicker during such operations. This is not dangerous, but it can be annoying.
Some things to take care of
The 95LX doesn´t charge rechargeable batteries, as the newer HP palmtop
Make sure that you never put batteries in the wrong direction into the
battery tray! Even one battery wrongly placed can destroy the motherboard, especially
if you use rechargeables, which provide a much higher current when shortened than Alkalines.
Note that in the HP palmtops, a contact spring does not necessarily mean the minus pole of the battery!
The Infrared port of the 95LX works only up to a data rate of 2400 baud, but the
IR diode is much more powerful than the IR diodes of the other palmtop models.
So it can be used very well for remote-control the TV or HiFi using
Last Updated on Tuesday, 16 March 2010