DayStar Digital TURBO 040, User Manual

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Full Speed Memory Locking
- (The
Default is on.) The Mac ROM on the Ilci and
older m achines provides a feature w hich
allows add-in hardware to lock sections of
m otherboard m em ory so that they can
write to it directly. On the Quadras, Mac
IIvx and others, this function causes a page
(8K) of m em ory to be marked as not
cacheable. All other parts of RAM are still
cacheable and still operate at full speed. The
locked page of memory, however, will
always remain uncacheable and thus will
not benefit from the internal (on-chip) or
secondary caches.
On the older machines, however, the m em o­
ry locking is very inefficient. If any block of
m em ory is ever locked, the Mac will
turn
off the 68040’ s internal data cache
while
the M acintosh is running. Since the majori­
ty of the speed increase of the 68040 is due
to the on-chip caches, there will only be a
very small perform ance increase w hen any
m em ory is locked and the Turbo 040 is
installed. The instruction cache is still
enabled, so program s will EXECUTE faster,
but all data operations will be uncacheable
and will not even benefit from the sec­
ondary caches.
Full Speed Memory Locking
- Gives Ilci
and older Mac ow ners the sam e capabilities
as those with newer Macintoshes. W hen
this feature is enabled, it leaves the data
cache on for all parts of m em ory except the
m em ory that was specifically locked. This
option takes effect immediately, so reboot­
ing is not required.
Note:
Owners of the Apple 8-24 GC must
remove the GC software from their System
Folder in order to use Full Speed M emory
Locking.
C H A P T E R 9
Installing The Turbo 040 Software