1. What is Memory?
2. What do I need RAM For?
3. What's the difference between memory and storage?
4. Can you tell by looking at a module if it is SDRAM, FPM, EDO etc?
5. What is the difference between ECC and parity?
6. What is a refresh rate and self refresh?
7. What is the difference between Gold and Tin contacts?
8. What is the difference between buffered and registered?
9. What is the difference between 2-clock and 4-clock?
10. What is CL or CAS Latency?
11. What is the difference between CL2 and CL3?
12. What is an EPROM or EEPROM?
13. What is the difference between SPD and PPD?
14. What is OEM Memory?
15. What is Credit Card Memory?
16. What is PCMCIA Memory Card?
17. What is Flash RAM?
18. What are a few examples of Flash memory?
19. What is BIOS and how does it work?
20. What is ReadyBoost and how does it work?
21. What is PIO Mode and how does it work?

1. What is memory?

People in the computer industry commonly use the term "memory" to refer to RAM (Random Access Memory). RAM is a temporary storage area used to load program instructions and to store files currently in use. Random comes from the fact that the CPU can retrieve information from any single location, or address, within the RAM.

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2. What do I need RAM for?

While a computer is running, it uses its memory to hold the operating system, the applications you're working in (word processing, database, illustration program, etc.) and the files or documents you're working on. If you don't have enough RAM to hold all of this information at once, many computers can be set up to use the hard drive to store the overflow. This is known as using virtual memory, the swap file, or the scratch disk. The data path from the computer's Central Processing Unit (CPU) to the hard drive is much slower than the data path to the RAM chips. Also the RAM chips move data around inside themselves much faster than hard drives can. As a result, a computer with less RAM may take significantly longer to perform tasks than a computer with an identical CPU and more RAM. Also, computers with insufficient RAM may have more memory errors, more general protection faults, more system crashes.

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3. What's the difference between memory and storage?

People often confuse the terms memory and storage, especially when describing the amount they have of each. The term memory refers to the amount of RAM installed in the computer, whereas the term storage refers to the capacity of the computer's hard disk. RAM is only active when the computer is operating properly. Information stored on the hard drive, on the other hand, remains intact whether the computer is running or not. This is why it is important to save your work often, so that if the computer crashes, or if power is interrupted and your computer suddenly shuts off, you only lose what you've done since you last saved.

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4. Can you tell by looking at a module if it is SDRAM, FPM, EDO etc?

SDRAM, EDO and FPM chips look similar to each other. By looking at a memory module one cannot tell what it is. The best way to tell the difference is to reference the part number on the chip. Most DRAM manufacturers have reference books or lists on their WEB sites.

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5. What is the difference between ECC and parity?

Parity is a form of error detection, which can detect memory errors and halt the system to prevent data corruption. ECC memory is more complex form of error detection which not only detects, but also corrects most memory errors while your system is running.

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6. What is a refresh rate and self refresh?

A memory module is made up of electrical cells. The refresh process recharges these cells, which are arranged on the chips in rows. The refresh rate refers to the number of rows that must be refreshed. The common refresh rates are 2K, 4K and 8K. The 2K components are capable of refreshing more cells at a time and they complete the process faster, therefore 2K components use more power that 4K or 8K refresh. The 4K components are capable of refreshing less cells at a slower time, but they use less power. Some specially design DRAMs feature self refresh technology, which enables the components to refresh on their own -- independent from the CPU or external refresh circuits. Self refresh, which is built into the DRAM itself, reduces power consumption, and it is commonly used in notebook computers.

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7. What is the difference between Gold and Tin contacts?

The general overall rule is to match gold leads with gold contacts and tin leads with tin contacts. When you mix the two metals you speed up the natural process of corrosion. During this corrosion process a small electrical current can be formed (much in the way of how batteries work. Batteries contain an acid that is in a chamber with metal discs, the acid excels the corrosion process to create an electrical current.) and can cause problems with the way your RAM functions. When upgrading, confirm what type of connectors and leads you have, then order the same. This rule will not always work since it may not be possible to get the correct match of gold leads with gold contacts and tin leads with tin contacts.

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8. What is the difference between buffered and registered?

A buffer is a device used on EDO or Fast Page Mode modules. A register is used on SDRAM modules. Registers and buffers “re-drive” or “amplify” signals as they enter the memory module.

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9. What is the difference between 2-clock and 4-clock?

SDRAM requires clock lines running from the system clock to the memory module. Two clock means there are two clock lines running to the module, and four clock means there are four clock lines running to the module. Four clock designs are faster because they allow less chips per clock line, enabling a quicker interface with data.

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10. What is CL or CAS Latency?

CL stands for CAS Latency. It is a programmable register in the SDRAM that sets the number of clock cycles between the issuance of the READ command and when the data comes out. Smaller number for CL indicates faster SDRAM within the same frequency.

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11. What is the difference between CL2 and CL3?

CL2 (CAS Latency 2) is a little bit faster than CL3 (CAS Latency 3) because during one step in the column accessing process you only have to wait two clock cycles instead of three clock cycles. The overall performance difference is minor, but some systems are designed to only support one type of memory or the other. When ordering memory, use memory.com’s configuration tools to find the part number you need. memory.com’s system- specific part numbers guarantee that you will get the correct technology based on what your motherboard supports.

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12. What is an EPROM or EEPROM?

EPROM (Erasable Programmable Read-Only Memory) was designed to allow changes to the ROM chips through the use of ultra-violet light. A window on the top of an EPROM chip allows you to reprogram the chip using a chip burner. This system works, but because outside equipment was required not many people used this system. The chip can be programmed with various types of information about the memory module, and the CPU uses this information when booting up to understand what kind of memory is in the system and adjust its settings accordingly.
EEPROM (Electrically Erasable Programmable Read-Only Memory) allows technicians to flash an electric charge through the ROM chip to reprogram it's code. Most current BIOS's have EEPROMs, and can be flashed while still connected to the motherboard. This means that a simple software utility can re-write an entire BIOS.

EPROM's are used on most present day SDRAM modules. When a memory module is assembled, in addition to the precision SDRAM chips, there must also be a correctly programmed SPD (Serial Presence Detect) EEPROM. The SPD EEPROM is a small little black chip found near the edge of the module. It is normally located on the right hand corner of the module, near pin 84 if you count from left to right.

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13. What is the difference between SPD and PPD?
When a computer system boots up, it needs to “detect” the configuration of the memory modules in order to run properly. PPD (Parallel Presence Detect) is the more traditional method of using a number of resistors to relay the required information, and SPD (Serial Presence Detect), a more recent method, uses an EPROM to store information about the module. SPD can store over 400 times as much information as PPD, and is becoming more prevalent.

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14. What is OEM Memory?

OEM is an acronym for "original equipment manufacturer" and OEM memory means that the memory chips and PCB boards are made by the semiconductor manufacturer themselves, and the same memory that the largest PC manufacturers worldwide such as Dell, Compaq, Apple buy for use as original equipment in their systems.

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15. What is Credit Card Memory?

Credit card memory is a proprietary self-contained DRAM memory module that plugs into a special slot for use in notebook computers.

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16. What is PCMCIA Memory Card?

Another self-contained DRAM module for notebooks, cards of this type are not proprietary and should work with any notebook computer whose system bus matches the memory card's configuration.

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17. What is Flash RAM?

Flash RAM is a generic term for the small amount of memory used by devices like TVs, VCRs and car radios to maintain custom information. Even when these items are turned off, they draw a tiny amount of power to refresh the contents of their memory. This is why every time the power flickers, the VCR blinks 12:00. It's also why you lose all presets on your radio when your car battery dies! Your computer has Flash RAM to remember things like hard disk settings.

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18. What are a few examples of Flash memory?

Your computer’s BIOS Chip
Compact Flash (most often found in digital cameras)
Smart Media (most often found in digital cameras)
Memory Stick (most often found in digital cameras)
PCMCIA Type I and Type II memory cards (used as solid-state disks in laptops)
Memory cards for video game consoles

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19. What is BIOS and how does it work?

One of the most common uses of Flash memory is for the basic input/output system of your computer, commonly known as the BIOS (pronounced "bye-ose"). On virtually every computer available, the BIOS makes sure all the other chips, hard drives, ports and CPU function together.

Every desktop and laptop computer in common use today contains a microprocessor as its central processing unit. The microprocessor is the hardware component. To get its work done, the microprocessor executes a set of instructions known as software. You are probably very familiar with two different types of software:

The operating system - The operating system provides a set of services for the applications running on your computer, and it also provides the fundamental user interface for your computer. Windows 98 and Linux are examples of operating systems.

The applications - Applications are pieces of software that are programmed to perform specific tasks. On your computer right now you probably have a browser application, a word processing application, an e-mail application and so on. You can also buy new applications and install them.

The BIOS - The BIOS software has a number of different roles, but its most important role is to load the operating system. When you turn on your computer and the microprocessor tries to execute its first instruction, it has to get that instruction from somewhere. It cannot get it from the operating system because the operating system is located on a hard disk, and the microprocessor cannot get to it without some instructions that tell it how. The BIOS provides those instructions. Some of the other common tasks that the BIOS performs include:

§ A power-on self-test (POST) for all of the different hardware components in the system to make sure everything is working properly
§ Activating other BIOS chips on different cards installed in the computer - For example, SCSI and graphics cards often have their own BIOS chips.
§ Providing a set of low-level routines that the operating system uses to interface to different hardware devices - It is these routines that give the BIOS its name. They manage things like the keyboard, the screen, and the serial and parallel ports, especially when the computer is booting.
§ Managing a collection of settings for the hard disks, clock, etc.

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20. What is ReadyBoost and how does it work?

Windows ReadyBoost-capable Flash Devices extend the disk caching capabilities of Windows Vista main memory. ReadyBoost-capable devices can be implemented as USB 2.0 flash drives, Secure Digital (SD) cards, or CompactFlash cards. Using ReadyBoost-capable flash memory devices for caching allows Windows Vista to service random disk reads with performance that is typically 8-10 times faster than random reads from traditional hard drives.

An external ReadyBoost-capable device might be removed at any time, but ReadyBoost technology ensures there is no interruption of system service or loss of data. All data writes are made to the hard disk before being copied to the flash device, so every bit of data held within the flash device is safely duplicated on the hard disk. ReadyBoost also encrypts the content for use only on the PC system where the data was generated.

21. What is PIO Mode and how does it work?

This is the PIO mode setting for the IDE device. IDE/ATA uses one of two different ways to transfer information into and out of memory: either programmed I/O (PIO) or direct memory access (DMA). There are 5 different PIO modes, from 0 to 4, with 4 being the fastest. Newer drives support the faster modes.

You will normally want to select the highest mode that your drive supports. If you experience difficulties you may want to try to drop the mode down to a slower level, but this will impact performance.

Note: IDE autodetection will set this value automatically on most BIOSes, but on some this must be manually set; the autodetection won't do it.