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**82495DX/490DX DX CPU-Cache Chip Set <Sep91
***Notes:
date source: none direct, however:
InfoWorld Jan 20, 1992 p98 - Compaq Deskpro 486/50L
mentions it has this chip
Network World Sep 2, 1991 p20 - Advert for new Compaq Deskpro 486/50L
mentions 256K cache
so assumed to be sometime before sept 1991.
Information taken from: 82495DX.pdf (Oct '92)
***Info:
The 50 MHz Intel486 DX CPU-Cache Chip Set provides a high performance
solution for servers and high-end desktop systems. This binary
compatible solution has been optimized to provide 50 MHz, zero wait
state performance. The CPU-Cache chip set combines the 50 MHz Intel486
Microprocessor with the 82495DX/82490DX cache subsystem. It delivers
integer performance of 41 V1.1 Dhrystone MlPs and a SPEC integer
rating of 27.9. The cache subsystem features the 82495DX Cache
Controller and the 82490DX Dual Ported Data RAM. Dual ported buffers
and registers of the 82490DX allow the 82495DX Cache Controller to
concurrently handle CPU bus, memory bus, and internal cache operations
for maximum performance.
The CPU-Cache Chip Set offers many features that are ideal for multi-
processor based systems. The Write-Back feature provides efficient
memory bus utilization by reducing bus traffic through eliminating
unnecessary writes to main memory. The CPU-Cache chip set also
supports MESI protocol and monitors the memory bus to guarantee cache
coherency.
The 50 MHz Intel486 DX CPU and 82495DX/82490DX Cache subsystem are
produced on Intel's latest CHMOS V process which features submicron
technology and triple layer metal.
3.0 ARCHITECTURAL OVERVIEW
3.1 Introduction
The Intel486 CPU-cache chip set provides a tightly coupled processing
engine based on the Intel486 microprocessor and a cache subsystem
comprised of the 82495DX cache controller and multiple 82490DX cache
components. Figure 3.1 [see datasheet] diagrams the basic config-
uration.
The cache subsystem provides a gateway between the CPU and the memory
bus. All CPU accesses that can be serviced locally are transparent to
the memory bus and serve to avoid bus traffic. As a result, the cache
chip set reduces memory bus bandwidth to both increase Intel486
processor performance and support efficient multiprocessor systems.
The cache subsystem also decouples the CPU from the memory bus to
provide zero-wait-state operation at high clock frequencies while
allowing relatively slow and inexpensive memories.
The CPU-cache chip set prevents latency and bandwidth bottlenecks
across a variety of uniprocessor and multiprocessor designs. The
processor’s on-chip cache supports a very wide CPU data bus and
high-speed data movement. The second-level cache greatly extends the
capabilities of the on-chip cache resources, enabling a larger portion
of memory cycles to be satisfied independently of the memory bus.
3.2 CPU-Cache Chip Set Description
The chip set is comprised of three functional blocks:
3.2.1 CPU
The chip set includes a special version of the Intel486DX micropro-
cessor at 50 MHz. The Intel486DX Microprocessor Data Sheet provides
complete component specifications.
3.2.2 CACHE CONTROLLER
The 82495DX cache controller is the main control element for the chip
set. providing tags and line states. and determining cache hits and
misses. The 82495DX executes all CPU bus requests and coordinates all
main memory accesses with the memory bus controller (MBC).
The 82495DX controls the data paths of the 82490DX cache components
for cache hits and misses and furnishes the CPU with needed data. The
controller dynamically adds wait states as needed using the most
recently used (MRU) prediction algorithm.
The 82495DX also performs memory bus snoop operations in shared memory
systems and drives the cycle address and other attributes during
memory bus accesses. Figure 3.2 [see datasheet] diagrams the 82495DX.
3.2.3 CACHE SRAM
Multiple 82490DX cache components provide the cache SRAM and data
path. Each component includes the latches, muxes and logic needed to
work in lock step with the 82495DX to efficiently serve both hit and
miss accesses. The 82490DX components take full advantage of VLSI
silicon flexibility to exceed the capabilities of discrete
implementations. The 82490DX components support zero-wait-state hit
accesses and concurrent CPU and memory bus accesses, and they
replicate MRU bits for autonomous way prediction. During memory bus
cycles. the 82490DX components act as a gateway between CPU and memory
buses. Figure 3.3 [see datasheet] diagrams an 82490DX cache component.
3.3 Secondary Cache Features
The 82495DX cache controller and 82490DX cache components provide a
unified, software transparent secondary data and instruction cache.
The cache enables a highspeed processor core that provides efficient
performance even when paired with a significantly slower memory bus.
The secondary cache interprets CPU bus cycles and can service most
memory read and write cycles without accessing main memory. I/O and
other special cycles are passed directly to the memory bus. The cache
has a dual-port structure that permits concurrent CPU and memory bus
operation.
The 82495DX cache controller contains the 8K tag entries and logic
needed to support a cache as large as 256K. Combinations of between 4
and 9 82490DX cache SRAMs are used to create caches ranging from 128K
to 256K, with or without data parity.
The MBC provides logic needed to interface the CPU, 82495DX and
82490DX to the memory bus. Because the MBC also affects system
performance. its design can be the basis of product differentiation.
***Configurations:...
***Features:...
**82495XP/490XP Cache Controller / Cache RAM (for i860) 06/05/91...
**82496/491 Cache Controller / Cache RAM (for P5 Pentium) 03/22/93...
**82497/492 Cache Controller / Cache RAM (for P54 Pentium) <Nov94...
**82498/493 Cache Controller / Cache RAM (for P54 Pentium) <Nov94...
**
**Later chipsets (basic spec):
**440 series:...
**450NX (?) 06/29/98:...
**????? (Profusion) c:99...
**800 series...
*Headland/G2...
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*TI (Texas Instruments)...
*UMC...
*Unresearched:...
*VIA...
*VLSI...
*Western Digital...
**Other Chips:
SYSTEMS LOGIC/PERIPHERAL DEVICES
WD16C451, WD16C551 - Enhanced Asynchronous Communications Element (ACE) with Parallel Port
WD16C452, WD16C552 - Dual Enhanced Asynchronous Communications Element (ACE)
WD16C550 Enhanced Asynchronous Communications Element (ACE) with FIFOs
WD76C10AlLP/LV ISA-Based System Controller for 80386SX and 80286 Desktop and Portable Compatibles
WD76C20/LV Floppy Disk Controller, Real Time Clock, IDE Interface, and Support Logic Device
WD76C30/LV Peripheral Controller, Interrupt Multiplexer, and Clock Generator Device
WD7710/LP ISA-Based System Controller with Cache for 80386SX and 80286 Desktop and Portable Compatibles
WD7910/LP ISA-Based System Controller with Cache for 80386SX and 80286 Desktop and Portable Compatibles
IMAGING DEVICES
ICS90C61A Dual Video/Memory Clock Generator
ICS90C63 Dual Video/Memory Clock Generator
ICS90C64 Dual Video/Memory Clock Generator
WD90C00 VGA Controller (8514/A clone, max 1MB, 1024x768x16, 800x600x256)
WD90C01 8514/A for laptops
WD90C10 VGA, 256KB
WD90C11, WD90C11A Enhanced VGA Controller (max 512KB, 1024x768x16, 800x600x256)
WD90C20, WD90C20A VGA Flat Panel Display Controller (800x600x16, 640x460x256, 32 shades gray)
WD90C22 VGA Flat Panel Display Controller (800x600x16, 640x460x256, 64 shades gray)
WD90C24/A/A2 SVGA, max 1MB, 1280x1024x16, 1024x768x16, LCD, VESA-LB, 3.3 or 5V
WD90C26 VGA Flat Panel Display Controller
WD90C30 High Performance Video Controller (max 1MB, 1024x768x256, 1024x768x16)
WD90C31 Accelerator Video Controller (max 1MB, 1024x768x256, 1280x1024x16)
WD90C33 Same as WD90C31 but with, max 2MB, VESA-LB, 1280x1024x256, 1280x1024x16)
WD90C55 VGA LCD Interface
WD90C56 VLBI (Video Local Bus Interface), for WD90C30/31, VESA not mentioned.
WD9710 Pipelined, 32bit core, 64bit RAM, 24bit RAMDAC, PCI/VLB
WD9712 similar to WD9710
STORAGE DEVICES
WD10C01A Winchester Disk Controller
WD10C27 Data Separator
WD33C92A Enhanced SCSI Bus Interface Controller
WD33C93B Enhanced SCSI Bus Interface Controller
WD33C95A, WD33C96A Enhanced Single-ended and Differential SCSI Bus Interface Controller
WD37C65C Floppy Disk Subsystem Controller Device
WD42C22C Winchester Disk Subsystem Controller Device
WD60C318 Optical Disk Drive Encoder/Decoder
WD60C40A Peripheral Cache Manager Device
WD60C80 Error Detection and Correction Chip (EDAC)
WD61C23A High Performance Hard Disk Controller
WD61C40A Peripheral Cache Manager Device
WD7000 ESDI Controller (16-bit ISA)
WD7193 Fast SCSI-II PCI adapter, 33C296A-ZX chip
WD7197 Fast Wide version of WD7193
WD7296A Fast Wide SCSI-II (PCI?), possibly WD34C296 chip
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