http://www.worldofspectrum.org/ZXSpe.../sp128p09.html - использование из Бейсик-128
http://www.fruitcake.plus.com/Sincla...um128_ROM0.zip - дизасемблер ROM-0 (Бейсик-128) с комментариями (англ.)

В файле с исходным кодом ПЗУ-0 масса информации по теме. Словосочетание для поиска: RAM disk

Вот, например, оттуда:

Код:
; -----------------
; Logical RAM Banks
; -----------------
; Throughout ROM 0, memory banks are accessed using a logical numbering scheme, which
; maps to physical RAM banks as follows:
;
; Logical Bank   Physical Bank
; ------------   -------------
;     $00             $01
;     $01             $03
;     $02             $04
;     $03             $06
;     $04             $07
;     $05             $00
;
; This scheme makes the RAM disk code simpler than having to deal directly with physical RAM bank numbers.
Код:
; ------------------
; RAM Disk Catalogue
; ------------------
; The catalogue can occupy addresses $C000-$EBFF in physical RAM bank 7, starting at $EBFF and growing downwards.
;
; Each entry contains 20 bytes:
;   Bytes $00-$09: Filename.
;   Bytes $0A-$0C: Start address of file in RAM disk area.
;   Bytes $0D-$0F: Length of file in RAM disk area.
;   Bytes $10-$12: End address of file in RAM disk area (used as current position indicator when loading/saving).
;   Byte  $13    : Flags:
;                     Bit 0   : 1=Entry requires updating.
;                     Bits 1-7: Not used (always hold 0).
;
; The catalogue can store up to 562 entries, and hence the RAM disk can never hold more than 562 files no matter
; how small the files themselves are. Note that filenames are case sensitive.
;
; The shadow screen (SCREEN 1) also resides in physical RAM bank 7 and so if more than 217 catalogue
; entries are created then SCREEN 1 will become corrupted [Credit: Toni Baker, ZX Computing Monthly].
; However, since screen 1 cannot be used from BASIC, it may have been a design decision to allow the
; RAM disk to overwrite it.
;
; The actual files are stored in physical RAM banks 1, 3, 4 and 6 (logical banks 0, 1, 2, 3),
; starting from $C000 in physical RAM bank 1 and growing upwards.
;
; A file consists of a 9 byte header followed by the data for the file. The header bytes
; have the following meaning:
;   Byte  $00    : File type - $00=Program, $01=Numeric array, $02=Character array, $03=Code/Screen$.
;   Bytes $01-$02: Length of program/code block/screen$/array ($1B00 for screen$).
;   Bytes $03-$04: Start of code block/screen$ ($4000 for screen$).
;   Bytes $05-$06: Offset to the variables (i.e. length of program) if a program. For an array, $05 holds the variable name.
;   Bytes $07-$08: Auto-run line number for a program ($80 in high byte if no auto-run).