Cito trozo de la explicación (en inglés)
El link para ver más del tema es el siguiente:The ZX97 design goals include:
1. Compatability with 64K stock ZX81 BASIC and machine code software and all varieties of high resolution software including those that require special hardware (static RAM, modified 16K, etc).
Most ZX81 software uses ZX81 ROM routines and the default ZX97 operating system should therefore be a minimally modified ZX81 ROM.
OS extensions including Hires Basic commands can be added using a new ROM address space (ie bank switching) and a few simple hooks in the existing ROM. (also see F.)
2. A flexible character pattern generator: instead of only one set of 64 characters patterns and their inverse, we add additional sets of UDGs (user definable characters).
3. The stock ZX97 of course needs to have 64K memory to meet the basic design objective of (expanded) ZX81 compatability. But a single 128K SRAM is the simplest way to achieve this. By the same token, alternate OS and utility programs in firmware could use a 128Kbyte EPROM. This way we buy a lot of extra power using the same number of chips at little extra cost.
Needless to say the RAM is battery backed up and must be selectively write protected!
4. 256K Memory management: now that we talked ourselves into using 128K RAM and EPROM chips we use a few I/O lines to do the bank switching
5. A flexible memory mapping circuit allows SHADOW RAM to be used instead of EPROM,
for example, in the 0-8K area for experimenting with OS software.
6. ZX81 compatability dictates the ZX97 0-8K ROM is virtually identical to the ZX81 ROM.
However OS extensions need to hook into the existing operating system.
I propose a new set of keywords which use a new "X" cursor mode in addition to the existing "K" , "L" and "F" cursor modes.
Like the "F" mode, the "X" mode uses SHIFT ENTER but is followed by an additional ENTER to chang the cursor to "X" and then a single keystroke selects any of up to 38 new keywords.
7. Serial and parallel I/O enables connecting and comunicating with other computers or printers.
I propose emulating an existing commercial product to take advantage of existing software support.
Espero que le haya sido de su agrado revisar este interesante documento.
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