1

HW3

Name some of the third-party CMOS save-and-restore utility programs ?

CHAPTER 7

MEMORY

Chapter Overview

ROM and RAM Memory Mapping

Defining Memory

Memory is the area within a computer where information is stored while being worked on. 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

Computer memory includes two major classes. 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) 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)

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 Includes two common forms

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.

capacitor

transistor

Refreshing Circuit ++++++++

Capacitor 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)

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

DDR memory

SDRAM memory

DRAM memory

Data integrityThere are two primary methods of ensuring that the data received is the same as the data sent.

Parity Error-correction encoding (ECC)

RAM cont.

Parity

Is a method of ensuring data integrity that add an extra bit ( the parity bit) along

with each 8-bit bus cycle.

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.

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.

Bus Cycle

Access speed

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

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)

RAM Packaging

SIPP (single inline pinned package)

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

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.

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

Memory Configuration Cont.

There are some rules to follow when banking

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

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

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)

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 MappingIdentify and Manage Memory (how memory is allocated)

Hexadecimal Code

Memory AllocationUses 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 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 Is a specification that allows multiple applications to access extended memory

at the same time.

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 In protected mode multiple tasks can take

place at the same time. In real mode only one operation at a time.

Shadow RAM

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 DisplayMEM.COM Display

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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

Chapter Summary 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.

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Quiz 3 Sunday, 22nd of April ( LAB

time) Quiz Materials: Chapter 7

( Memory)