NEC MH4500 - Manual (Page 17)

System Overview 1-9
The IDE controller features:
T PIO and IDE DMA/bus master operations
T Mode 4 timings
T transfer rates up to 22 MB/second
T buffering for PCI/IDE burst transfers
T master/slave IDE mode.
SCSI Controllers
The system board contains two SCSI controllers: a narrow SCSI controller
(SYM53C810AE) on the PCI-A bus, and a dual-channel wide LVD/SE
(Ultra2/Ultra) SCSI controller (SYM53C896) on the PCI-B bus. The narrow
controller provides support for legacy 8-bit SCSI devices in the 5 1/4-inch drive
bays, including the factory installed SCSI CD-ROM drive. The wide controller
drives one SCSI backplane and provides support for external expansion.
Internally, each wide channel is identical, capable of operations using either
8- or 16-bit SCSI providing 10 MB/sec (Fast-10) or 20 MB/sec (Fast-20)
throughput, or 20 MB/sec (Ultra), 40 MB/sec (Ultra-wide) or 80 MB/sec
(40 MHz) (Ultra-2).
The SYM53C810AE (narrow) contains a high-performance SCSI core capable
of Fast 8-bit SCSI transfers in single-ended mode. It provides programmable
active negation, PCI zero wait-state bursts of faster than 110 MB/sec at 33 MHz,
and SCSI transfer rates from 5 to 10 MB/sec. The narrow SCSI comes in a
100-pin rectangular plastic quad flat pack (PQFP).
The Sym53C896 (wide) contains a high-performance SCSI bus interface. It
supports SE mode with 8-bit (10 or 20 MB/sec) or 16-bit (20 or 40 MB/sec)
transfers and LVD mode with 8-bit (40 MB/sec) or 16-bit (80 MB/sec) transfers
in a 329-pin ball grid array (BGA) package.
Each controller has its own set of PCI configuration registers and SCSI I/O
registers. As a PCI 2.1 bus master, the SYM53C896 supports burst data
transfers on PCI up to the maximum rate of 132 MB/second using on-chip
buffers.
In the hot-swap bay, the system supports up to six, one-inch high SCSI hard disk
drives. Also, in the 5 1/4-inch bays, the system supports three SCSI or IDE
devices (the SCSI controller itself supports more devices, but the 5 1/4-inch bay
can only hold a maximum of three devices).
A wide SCSI cable provides two connectors for Ultra SCSI devices, one of
which is used for the SCSI backplane. However, SCSI devices do not need to
operate at the ultra transfer rate. All drives on the bus must be Ultra-2 (LVD) to
run at 80 MB/sec (40 MHz). The 5, 10, and 20 MHz operations can coexist on
the bus and each device interacts at its appropriate speed.