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19
2 System Board
Devices on the PCI Bus
The three DMA modes allow the following transfer rates:
Operated in slave mode, the IDE controller saturates the PCI bus with
transfers, thus limiting the actual achieved transfer rate to 10 MBytes per
second. Operated in master mode, though, the IDE controller is allowed to
work autonomously of the processor, and the full 16.7 MBytes per second
transfer rate can be achieved, with less than 33% occupancy of the PCI bus
(so allowing the processor to get on with other work for more than 67% of
the cycle times, whilst the IDE transfers are going on in parallel).
Disk Capacity Versus
Modes of Addressing
The amount of addressable space on a hard disk is limited by three factors:
the physical size of the hard disk, the addressing limit of the IDE hardware,
and the addressing limit of the BIOS. The Extended-CHS addressing scheme
allows larger disk capacities to be addressed than under CHS, by performing
a translation (for example regrouping the sectors so that there are twice as
many logical tracks as is possible under the CHS addressing scheme).
If the
Setup
field has been set to
automatic
, the logical block addressing
(LBA) mode will be selected for each device that supports it.
Mode
0
1
2
Cycle time (ns)
480
150
120
Transfer rate (MBytes/s)
4.2
13.3
16.7
Cylinders per
Device
Heads per
Cylinder
Sectors per Track
Bytes per
Sector
Bytes per
Device
CHS
64
16
1024
512
528 M
ECHS
64
256
1024
512
8.4 G
LBA
-
-
256 M (=2
28
)
512
137 G
Содержание Vectra VE5 3
Страница 1: ...Technical Reference Manual Hardware and BIOS HP Vectra VE series 3 PC ...
Страница 8: ...Contents viii ...
Страница 16: ...8 1 System Overview Documentation ...