ACT apricot - Multi-Sector Reads and Writes; Tri-Buffer

SOFTWARE
Multi-sector Reads and Writes
The 8089 Input/Output Processor has been programmed
to perform submerged (in the 'background' or simultaneous
with 8086 operations) disk read and write functions on
multiple sectors. This increases the speed of most disk
operations
and fits into the philosophy of MS-DOS 2.0
multiple driver request operations.
Tri-buffer
1. Disk Cache Memory. The cache memory is used by the
disk driver to hold a number of disk sectors, and operates in
the following manner:
Disk
READ
Disk
WRITE
The disk driver, on receiving a request for a
sector
to be read, first examines the cache to
find out if the sector is resident in memory. If
resident, the sector is immediately returned to
the DOS. If not resident, the sector will be read
from disk and if there is room within the cache,
the sector is saved, as well as returned to the
DOS. If there is no space, the cache overwrites
the sector image within the cache which has
not been accessed for the longest period of time
with the new sector.
When a disk write request is made to the disk
driver,
the sector is written to disk as well as
being saved
within the cache. If there is no
space, again the sector image within the cache
not accessed for the longest period of time is
overwritten with the new one. All sector writes
to disk are performed in the background, so the
BIOS does not need to wait around until the
operation is complete before returning to the
DOS. This background operation is possible
because of
the 8089 lOP and the cache.
2. Print buffer. The Print buffer has the same effect on
printing as the disk cache on disk writes. To the DOS and
the user, printing occurs at a much faster rate.