Home > Articles

Memory: Types and Forms

This chapter is from the book

Terms you'll need to understand:

  • Volatile and nonvolatile
  • Memory register and memory cell
  • BIOS and CMOS
  • Synchronous (synchronized), and asynchronous (not synchronized)
  • Cache hierachy, cache, buffer
  • Fast Page Mode (FPM), Extended Data Out (EDO) memory
  • RAM, DRAM, SRAM, SDRAM, RDRAM, DDR-SDRAM, VRAM
  • DIP, SIMM, DIMM, RIMM
  • Parity, ECC

Concepts you'll need to master:

  • Read-only memory (ROM), Programmable ROM (PROM), and Random Access Memory (RAM)
  • Memory address, grids, and matrix
  • Memory refresh and wait states
  • Clock multipliers
  • Secondary memory caching, internal and external memory
  • Memory pages
  • Chip packaging and modular manufacturing
  • Odd and even parity, error detection

Perhaps the most familiar parts of a computer are the central processing unit and the main memory. The main memory is the same as the "computer's memory," also commonly referred to as system memory, or RAM. In this chapter we examine memory chips and how they're packaged. In Chapter 5, "Processors and Chipsets," we then look at different types of processors.

Memory is only a temporary place to store information until a device can get to it. Essentially, the CPU uses memory to move program instructions and data in and out of that temporary storage area. A typical instruction might be a request to store a data bit somewhere. Another instruction might be to retrieve that bit from a particular place—an address. Data might be a number, a letter, or any other bit of information. Remember that a data bit is also a small charge of electricity.

Data becomes information when it takes on context (surrounding circumstances). 76 means nothing on its own, other than the fact that it's a number. Surround that number with context: "Tomorrow, the temperature is expected to reach 76," and it becomes information. RAM is like a holding tank for data on its way to becoming information.

Storage is any location where information can be placed and retained for some amount of time. Computer memory is temporary storage, in that it generally requires the presence of electrical current. Volatile memory can hold information only when a normal electrical current is present. Nonvolatile memory can hold information in the absence of an electrical current. System memory is, for the most part, volatile.

Compact memory cards, smart memory cards, and memory sticks used in digital photography are examples of nonvolatile memory. Although some amount of current is necessary to change information, that information then remains stored even when there is no further current. Remember that volatile memory requires a continuing supply of current.

NOTE

Volatile, from the Latin "to fly," means that information "flies away" when there's no electricity to keep it in place. Television reporters often refer to an explosive situation as a volatile situation, meaning that it could change at any second. Volatile memory will lose all of its data when electricity is removed. Nonvolatile memory will maintain its data even without electricity.

Floppy disks, fixed disks, optical disks, and card media are all nonvolatile. However, although disks retain information without electrical current, we refer to them as permanent storage, not "memory." The terms volatile and nonvolatile are generally assigned to memory chips.

Permanence is a relative word. A burst of static electricity can completely wipe out any information on a magnetic storage device or in a memory chip. Optical disks store data in structural changes to the media, and so even ESD or close proximity to a magnet (electromagnetic interference) rarely affect that information. Chapter 6, "Basic Electronics," examines both ESD and EMI.

Conceptual Overview

Computer memory is fairly easy to remember when you've grasped the basic concepts. In a nutshell, a CPU uses transistors to handle bits of data. These transistors are grouped together into registers, making for small storage places inside the processor housing (the chip die). At some point, either the registers fill up or the instructions are completed. The CPU then works together with a memory controller to move data bits out to memory cells. Memory cells are typically capacitors that form small storage places on a memory chip. Both processor registers and memory cells have addresses. Every time a bit of data goes somewhere, it crosses a bus of some kind. That's it; now go pass the exam!

All right, so it's a bit—so to speak—more complicated than that. Most memory began as dynamic random access memory (DRAM). The main engineering changes that have taken place have all been attempts to find ways of either speeding up the memory to match CPU speeds, or to speed up the CPU to match memory speeds. The rest of memory technology relates to moving bits of information across buses more quickly.

TIP

When we refer to speeding up memory, we usually mean increasing the speed of the memory chips, increasing the clock speed of associated buses, or handling larger pieces of data.

To understand memory addresses, you should first understand a grid or matrix. We're therefore going to use Table 3.1 to a slightly different fashion, making it into a sort of "mind map." If you can see the way the overall types of memory break down on a grid, then perhaps they'll be easier to remember.

NOTE

A matrix is nothing more than an arrangement of columns and rows, like a spreadsheet or an Etch-a-Sketch. Columns go up and down across the page, and rows go left and right across the page. Remember the word "page." Column addresses are at the top; row addresses are along the side.

Cells going left to right (horizontally) in a row have an X coordinate. Cells going up and down (vertically) in a column have a Y coordinate. The direction of rows is called the X axis, and columns are called the Y axis. Combining X and Y coordinates gives us an address in the grid, like a cell address in a spreadsheet. A memory page is a range (group) of cell addresses within a row.

Table 3.1 Mind Map of Basic Memory Concepts

Permanent Storage/Nonvolatile Memory

Magnetic disks Optical disks Printed paper

Permanent

 

Swap files

Temporary

 

ROM BIOS Programmable ROM (Flash BIOS)

Nonvolatile

 

Memory cards

Nonvolatile

 

Volatile Memory

Acronym

Packaging

Random Access Memory

RAM

 

Dynamic RAM—main memory

DRAM

DIP

Static RAM Cache Memory (L-1 and L-2) CMOS—(uses trickle charge battery)

SRAM

SIMM or chip

Synchronous DRAM—main memory

SDRAM

DIMM

Rambus DRAM—main memory

RDRAM

RIMM

Double Data Rate SDRAM—main memory

DDR SDRAM

DIMM


NOTE

We discuss several additional types of memory in this chapter, but the A+ exam is focused primarily on the types listed in Table 3.1.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020