ZX 16K RAM Pack - Instructions for use

    This RAM Pack Will expand the memory capacity of your Sinclair Personal Computer to 16K
bytes (1k byte = 1024 units of storage, i.e. 1024 characters) - which is the maximum it can handle.
The Zx 16K RAM is not expandable in stages and so is supplied with the 16K of memory build it. All
you have to do is plug it onto the expansion edge connector at the back of your computer. It will take its
power from the existing power supply.

    IMPORTANT - Make sure that the computer is switched off before plugging or unplugging the memory.
Otherwise you may damage the RAM pack or computer - also the computer's operation will
be interrupted for a short while and it may get stuck in a 'non communicative' state. You will then
need to switch off and on again anyway. Any program that was in the computer will certainly be lost;
so if you think a particular program may need alot of memory, it is wise to plug the RAM pack
before entering it. As a guide,the computer's internal memory can handle 30-60 lines of program, but
things like large arrays or a lot of data can cut this down considerably.

    A little mental arithmetic should show that the computer can theoretically handle up to 960 program
lines when fitted with the expansion pack. In practice no program is likely to need this much
(no prizes for trying!) except programs with a lot of data. In fact, the only evidence the user sees of
the RAM pack's operation - apart from almost never running out of memory - is that the inverse 'K'
takes a little longer to appear after switching on. This is because the computer tests the memory after
switch on to see how much there is. The results of the test aren't directly available, but a simple mac-
hine code program can be used to reassure the operator that he or she really has got the memory avail-


1 POKE 18000, 33
2 POKE 18001, 11
3 POKE 18002, 0
4 POKE 18003, 57
5 POKE 18004, 68
6 POKE 18005, 77
7 POKE 18006, 201
8 PRINT (USR (18000) - 16373)/1024;"K"

If run on your computer without ram the RAM pack the answer will be 1K - the ammount of memory
present in the system. With the 16K RAM pack, however, the answer will be 16K. Note that this
program does not say how many bytes free for a program, only how many are available to the
computer, which will use some of them for the display file stack, etc.

This was donated to me from a good friend, It is an near-exact copy of the original document.


Actually, 32k ,48k, and 64k RAM modules were available for the TS1000/ZX81. However, only 16k was available for Basic programs; the rest could store data or machine code.

A third party also offered a 16k ram board with non-volutile memory, meaning that its memory was retained even when the computer was turned off. Small programs could be stored in this memory, and run later by transferring them to normal ram. No need to load from tape! The board could also be wired to replace the system ROM, so you could actually rewrite the computer's operating system, if you were really, really bored.


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