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5 Memory Map
The following memory map is broadly used. Specific installations may require alterations but you may forfeit functions in future FIG offerings.
The disc buffer area is at the upper bound of RAM memory. It is comprised of an integral number of buffers, each B/BUF+4 bytes. B/BUF is the number of bytes read from the disc, usually one sector. B/BUF must be a power of two (64, 128, 256, 512 or 1024). The constant FIRST has the value of the address of the start of the first buffer. LIMIT has the value of the first address beyond the top buffer. The distance between FIRST and LIMIT must be N*(B/BUF+4) bytes. This N must be two or more.
Constant B/SCR has the value of the number of buffers per screen; i.e. 1024 / B/BUF.
The user area must be at least 34 bytes; 48 is more appropriate. In a multi-user system, each user has his own user area, for his copy of system variables. This method allows reentrant use of the Forth vocabulary.
The terminal input buffer is decimal 80 bytes (the hex 50 in QUERY) plus 2 at the end. If a different value is desired, change the limit in QUERY. A parameter in the boot-up literals locates the address of this area for TIB. The backspace character is also in the boot-up origin parameters. It is universally expected that "rubout" is the backspace.
The return stack grows downward from the user area toward the terminal buffer. Forty-eight bytes are sufficient. The origin is in R0 (R-zero) and is loaded from a boot-up literal.
The computation stack grows downward from the terminal buffer toward the dictionary which grows upward. The origin of the stack is is in variable S0 (S-zero) and is loaded from a boot-up literal.
After a cold start, the user variables contain the addresses of the above memory assignments. An advanced user may relocate while the system is running. A newcomer should alter the startup literals and execute COLD. The word +ORIGIN is provided for this purpose. +ORIGIN gives the address byte or word relative to the origin depending on the computer addressing method. To change the backspace to control H type:
HEX 08 0E +ORIGIN ! ( byte addresses)
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