FLASH DISK


Flash Disk,  named for its speed and its effect on the screen, is 
a ram disk with a difference - it lets an Amstrad 1512 use up  to 
700K of RAM.

The  key  is the Amstrad's 64K of display memory,  of which  many 
programs  use  only  4K.  This device driver makes  the  graphics 
memory behave as a DOS disk.

Flash  disk  is  installed by putting the  file  FLASH.SYS  on  a 
bootable disk and adding a line to CONFIG.SYS as follows:

                        device=flash.sys

Flash  disk will be assigned the next free drive letter,  usually 
d:  if the machine has a hard disk, c: if it hasn't. A message is 
displayed during booting that says which it is.

The  normal  text  screen appears on the flash disk as  the  file 
SCREEN0.SYS,  with  three  extra text screens as  SCREEN1.SYS  to 
SCREEN3.SYS.  These  files  are place-holders  that  prevent  DOS 
overwriting  the  part of screen memory actually used by text  or 
medium  resolution  graphics.  This leaves 48K free for  the  ram 
disk. 

If the extra text screens and medium resolution graphics are  not 
required,  the  SCREEN1.SYS  to SCREEN3.SYS files can be  deleted 
(with  normal DOS delete commands) increasing the free  space  to 
60K.  The  SCREEN0.SYS  file  should  only be  deleted  for  very 
specialised systems that do not use the screen at all.

A  side  effect of the SCREEN files is that screen dumps  can  be 
made  very  easily from a program in any language by  reading  or 
copying the screen file.  The screen can similarly be loaded from 
file  by writing to SCREEN0.SYS.  The vital point to remember  is 
that the SCREENn files are at fixed positions in memory - copying 
to  them would change their position and cause chaos.  They  must 
only be written to in situ (eg by a Pascal reset, or an assembler 
open  handle,  never by a Pascal rewrite or an  assembler  create 
handle).

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In case the flash disk is not big enough, conventional RAM can be 
added to it.  This is controlled by a parameter in the CONFIG.SYS 
file,  a  slash  followed by the number of K memory to  add.  For 
example, to make a 100K disk using the 60K from screen memory and 
40K from normal RAM, put this line in CONFIG.SYS

                      device=flash.sys /40

and these in AUTOEXEC.BAT

del d:screen1.sys
del d:screen2.sys
del d:screen3.sys

(this assumes a hard disk is c: and the flash disk is d:)

Flash disk can optionally include error checking on all reads  to 
detect corruption of its memory by other programs.  This  feature 
is included by adding the parameter /c to the CONFIG.SYS file, as 
follows:

                       device=flash.sys /c

The  SCREENn  files should not be read when  using  this  option, 
because  they  will usually have been modified by  direct  screen 
output. This is corruption from Flash disk's point of view and it 
will report read errors through DOS.