Transcript Chapter Overview

HW3
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Name some of the third-party CMOS
save-and-restore utility programs ?
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CHAPTER 7
MEMORY
Chapter Overview
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ROM and RAM
Memory Mapping
Defining Memory
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Memory is the area within a computer where
information is stored while being worked on.
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Information is stored by using 0s and 1s as
switches.
By stringing a series of switches together, larger
numbers and code values can be represented.
Nonvolatile and Volatile Memory
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Computer memory includes two major
classes.
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Nonvolatile: computer retains data when the
power is shut off
Volatile: computer loses data when the power is
shut off
Completion: CMOS ROM is firmware or ……..?
Read-Only Memory (ROM)
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Is nonvolatile memory, generally installed during manufacturing
Protects the information required to start and run the computer
Holds instructions for performing the power-on self test (POST)
and basic input/output system (BIOS) information
Requires attention only if it needs to be replaced or upgraded
Random Access Memory (RAM)
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It Is a volatile memory
Used to hold temporary instructions and data for
manipulation while the system is running.
Term random is applied because the CPU can
access or place data to and from any addressable
RAM on the system.
DRAM and SDRAM
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Includes two common forms
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Dynamic RAM (DRAM)
 Works by using a microscopic capacitor and a microscopic transistor to store each
data bit. A charged capacitor represents a value of 1 and a discharge capacitor
represents a value of 0. it holds the charge and then releases it.
 DRAM needs complete set of circuitry just to keep the capacitors charged.
 The process of recharging these capacitors is called refreshing.
 DRAM is called volatile because without refreshing the data would be lost.
transistor
capacitor
Refreshing Circuit ++++++++
Capacitor
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A capacitor is an electrical device that can store energy in the
electric field between a pair of closely-spaced conductors (called
'plates'). When voltage is applied to the capacitor, electric charges of
equal magnitude, but opposite polarity, build up on each plate.
Synchronous DRAM (SDRAM)
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Other dynamic random access memories (DRAM)
have an asynchronous interface which means that
it react as quickly as possible to changes in control
inputs. SDRAM has a synchronous interface,
meaning that it waits for a clock signal before
responding to its control inputs. It is synchronized
with the computer's system bus, and thus with the
processor
Memory
SDRAM memory
DRAM memory
DDR memory
RAM cont.
Data integrity
There are two primary methods of ensuring that the data
received is the same as the data sent.
Parity
Error-correction encoding (ECC)
Parity
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Is a method of ensuring data integrity that add an extra bit ( the parity bit) along
with each 8-bit bus cycle.
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Two kinds of parity: even and odd
set the value of the parity bit based on the even or odd number.
The string goes into DRAM
The parity circuit checks the math. if the parity bit of the number that represents
the sum of the binary string sent, the data is passed on.
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ECC( error-correction coding)
It adds extra information about the bits, which is then evaluated
to determined if there are problems with individual bits in the data string.
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Bus Cycle
Access speed
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Denoted in nanoseconds (ns), is the amount of time
it takes for the RAM to provide requested data to the
memory controller.
Most 486 and Pentium based machines use either
70ns or 60 ns.
Please check page 123
RAM Packaging
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Early versions of RAM were installed in a single chips usually 1
bit wide DIP ( dual inline package).
To upgrade or add memory new chips had to be individually
installed on the M/B ( 8 or 9 chips per row- 9 if using parity)
SIPP (single inline pinned package)
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Is a printed circuit board with individual DRAM chip
mounted on it.
RAM Packaging
Various RAM
packages. From top
to bottom:
 DIP 16-pin,
 SIPP,
 SIMM 30-pin,
 SIMM 72-pin,
 SDRAM DIMM,
 DDR DIMM.
Memory Configuration
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8-bit data bus requires memory in 8-bit
chunk.
16-bit data bus requires memory in 16-bit
chunks.
32-bit data bus requires memory in 32-bit
chunks.
Memory Configuration Cont.
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Bank: it is used to describe the necessary rows of chips
as well as the slots into which they are inserted.
To calculate the number of SIMMs needed to make one
bank use the following formula: divide the number of
data bits per CPU cycle by the bit width of the module
32/8=4 modules per bank
Check page 126
There are some rules to follow when banking
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All rows in a bank must be either completely filled or
completely empty.
Each bank is numbered starting with bank 0.
In most system, DRAM should be installed in bank 0
before any other bank is used.
Refer to the motherboard documentation for bank
numbering and installation direction.
Specifying SIPPs and SIMMs
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Two values to determine how much memory
a unit can hold :
Width: 1 bit, 4-bit, 8-bit, 16 bit
Depth: how deep the chip is : 256KB, 1
MB…32MB.
You can determine the size of the DRAM chip
by combining the depth and width of the chip
Installing SIMMs
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Check the memory module voltage ( 5 or
30.3 volt).
Use electrostatic discharge (ESD) protection
and handle single inline memory modules
(SIMMs) carefully.
Insert the SIMM at a 45-degree angle and
click it into place. (The notch in the SIMM
prevents improper installation.)
DIMM( dual inline memory module)
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Package with 168 pins.
One card can form a complete bank.
Provide larger amount of RAM on a single
module and easy to install.
Cache Memory
 Caching in PC terms, is the holding of a recently or frequently used code or data in a
special memory location for rapid retrieval.
 Static RAM( SRAM): the high speed memory chip generally used for caching .
 SRAM uses a special circuit called a flip-flop.
 SRAM fast and it doesn't have to be refreshed .
 SRAM is more expensive than DRAM.
Internal cache (L1) : a cache has been included on every CPU.
External Cache(L2): this cache amounted directly on the M/B
Write back and write through: the primary use of a cache is to increase the speed of data
From RAM to the CPU.
Write through: CPU send all data directly to RAM.
Write back: send data directly to cache.( some caches store data
For a time and send it to RAM later.
Check page 132
Memory Mapping
Identify and Manage Memory (how memory is allocated)
Hexadecimal Code
Memory Allocation
Uses hexadecimal addresses to define ranges of memory.
The original processors developed by Intel were unable to use
more than 1 MB of RAM.
This 1 MB of memory divided into two sections: the First 640
KB was reserved for the O.S and applications ( designated as
conventional memory).
The remaining 384 KB of RAM (designated as upper memory)
used for BIOS, video and ROM.
Memory Allocation
Types of Memory Access
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Extended memory specification (XMS): RAM above the 1MB address is
called extended memory.
Extended memory is accessed through an extended memory manager
(HIMEM.SYS).
80286 up to 16 MB
80386 up to 4GB.
Conventional memory : is the amount of RAM typically 640 KB, addressable
by an IBM PC or compatible machine operating in real mode( real mode is the
only operating mode supported by MS-DOS)
MS-DOS protected mode interface
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Is a specification that allows multiple applications to access extended memory
at the same time.
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Expanded memory specification ( EMS):
Uses a 64KB section of memory to provide a “ window” in which data can be
written, the data is paged or swapped to and from the CPU through this window.
HMA( High Memory Area):
Intel chip architecture allowed MS-DOS to address the First 64KB of extended
memory, this special area is called HMA.
Protected mode and real mode
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In protected mode multiple tasks can take
place at the same time.
In real mode only one operation at a time.
Shadow RAM
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Shadow RAM is a copy of Basic Input/Output
System (BIOS) routines from read-only
memory (ROM) into a special area of random
access memory (RAM) so that they can be
accessed more quickly.
Shadow RAM
Determining Usable Memory
MEM.COM Display
Important Notes
I/O ports addresses start from 00 to FFh.
 Memory location and their locations.
 Example:
Keyboard send its data through port, address of
the port is 06H and CPU send the O/P to
printer through port 03H
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Chapter Summary
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The two basic computer memory types are
ROM (nonvolatile) and RAM (volatile).
RAM is packaged in a variety of designs.
Installing SIMMs requires ESD protection and
careful handling.
Cache memory enhances performance.
Hexadecimal code simplifies binary code
notation.
Memory allocation has been simplified under
Microsoft Windows.
Quiz 3
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Sunday, 22nd of April ( LAB time)
 Quiz Materials: Chapter 7
( Memory)
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