Hi,
I am going to share how I enabled option 1M on a Tektronix TDS754A. This can be done without opening the case. I am going to take you through the process that I used step by step.
*** Edit: This has also been tested successfully on a TDS744A ***Equipment ListCompaq Deskpro 2000 Pentium 133 MHz PC with an ISA bus slot
National Instruments GPIB PC II/IIA card
GPIB cable
SoftwareBorland C was used to compile the C program
The NI GPIB software drivers for DOS
Computer PreparationThe GPIB board was installed in the PC with the switches and jumpers set like this:

The board is configured for No DMA, IRQ 7 and base address 0x02E1.
The NI instrument drivers were installed. This puts the following line in Config.sys:

I then ran the NI utility IBCONFIG. I had to adjust the address to match the board address:
SoftwareI wrote a small program in C that will send the following commands to the scope.
send_scope("PASSWORD PITBULL");
send_scope("WORDCONSTANT:ATPUT 327686,1");
These are the lines in the program that actually enables the option.
I have attached the C code below in a file options_c.txt
I compiled the program with Borland C to make a DOS executable.
You will probably have to modify the program for other GPIB adapters. I made it work with the GPIB hardware that I already had.
Using the ProgramConnect the scope to the GPIB board with a cable.
Turn on the scope and wait for the boot to complete.
Access GPIB address menu from Utility -> I/O.
Set the GPIB address to 1: ( I hard coded the address to 1 in my program)

You now need to
unprotect the NVRAM. There is a switch located behind two holes in the cover as shown in this diagram:

Run the DOS program
Now set the
switch back to the protected position.
Turn the scope off and then back on. You should see 1M added to the options list:

If you go to the horizontal menu you should now be able to set the record length to 500,000 points for a single channel, 250,000 points for two channels and 125,000 points for four channels.

This process worked for me with the two TD754A scopes in my collection. It should be considered as experimental. You are advised to perform a back-up of your NVRAM. My scope had 32 AS7C164 RAM chips on each side of the board. The chips are 8K x 8 so 64 chips is 512K of acquisition memory.
Enjoy !!!
Regards,
Jay_Diddy_B
Acknowledgement: This process was pieced together from information found on this forum, Tek's forum and the Yahoo Group Tekscopes. Without this information this would have not been possible. Many thanks !!