Demystifying Memory

September 22, 2009 - 11:10 am

Keeping up with technology is like keeping up with the language used by kids. Once you’ve learnt what everything means, there’s a whole new set of terms to learn. So while it’s great for us that technology is continually improving, how do we make sense of all the new terms?

We’re going to cut through the mist of buzzwords and bring some clarity to the world of memory. We can’t help you understand your kids, but we can help you distinguish your RAM from your hard drive.

Memory

A good place to start, don’t you think? Alas, it can be an ambiguous term. Memory can refer to either permanent storage or temporary storage. It can be removable, or internal to a device. If somebody says memory, get them to clarify what they mean. Expect to hear some of the other terms on this page. Most commonly, memory tends to mean RAM.

Cache memory: A type of RAM that a computer can access very quickly that usually supplies the most frequently requested data or recently requested data.

DDR: Double Data Rate Synchronous Dynamic Random Access Memory (or also known as DDR SDRAM) is a type of computer memory that is a lot faster than SDRAM and can be differentiated by different pins. DDR2 and DDR3 simply offer better performance.

DIMM: Dual Inline Memory Module. A thin circuit board holding a number of DRAM chips. It has a strip of gold connectors running along one edge with one or more notches. The notches ensure the module will only fit into a memory slot the correct way around, and will only fit into slots designed for that particular type of memory.

ECC: Error Correcting Code. An additional component can be included on a memory module to detect and correct small errors. ECC memory is used in servers and workstations that run 24/7 and have high demands placed upon them.

EEPROM: Electrically Erasable Programmable Read Only Memory.  A type of memory that be erased and reprogrammed repeatedly. Unlike EPROM chips, EEPROMs do not need to be removed from the computer to be modified.

EPROM: Erasable Programmable Read Only Memory. Memory that can retain its data when the power has been switched off.

Frequency: The number of cycles per second that RAM operates at. Performance increases with frequency, although overall performance is also affected by latency.

Latency: The delay between a request being made to RAM and that request being fulfilled. There are various points of latency in RAM that are often quoted individually. Latency is measured in either cycles or units of time (in the order of pico- and nano-seconds). Lower latencies give better performance.

Non ECC: As the name suggests, Non ECC memory doesn’t feature the error correcting components that ECC memory has. Non ECC memory is used in the vast majority of computing devices.

PROM: Programmable Read Only Memory. A type of memory that can be programmed once after the device is made.

RAM: Very high speed storage used to hold information from running programs. Typically measured in Gigabytes, a modern PC might have around 3GB of RAM. Programs that deal with rich media, such as image and video editing software and modern computer games, may require hundreds of megabytes of memory each. A system with more RAM can run a greater number of programs at once before it starts to slow down. RAM is temporary storage – when the power is turned off its contents disappear. There are different types of RAM in any system, but the largest, most familiar type is Dynamic RAM, or DRAM.

ROM: Read Only Memory. A type of memory that cannot be modified.

SDRAM DIMM: Synchronous Dynamic Random Access Memory Dual In-line Memory Modules is dynamic random access memory (DRAM) that has a synchronous interface. SDRAM is widely used in computers; from the original SDRAM, further generations of DDR (or DDR1) and then DDR2 and DDR3 have entered the mass market, with DDR4 currently being designed and anticipated to be available in 2012.

A Kingston Technology SO-DIMM memory module

SO-DIMM: Small Outline DIMM. A smaller sized version of a DIMM. These are most commonly found in laptops but also in space saving desktop machines, such as the Apple iMac.

Storage

Hard disk drive (HDD): Permanent storage. Everything that needs retaining when a system is switched off is stored here, including program files and users files such as photos, emails and documents. It’s common to find hard disks that can hold hundreds of Gigabytes of data. Hard disks contain spinning “platters” that store data magnetically.

Hard disk drives store hundreds of gigabytes of data.

SSD (Solid State Disk): A relatively new type of hard disk that doesn’t use magnetic platters. Instead, flash memory chips are used. SSDs have no moving parts so they can be more reliable and use less power than traditional disks. They’re several times faster too, but at the moment can’t hold quite as much data.

A Kingston Technology SSD - fast and furious

Flash Memory

Class ratings: It is a measurement of speed for SD cards equal to 8 Mbit/s. The higher the class, the faster the minimum write speed.

Compact Flash: Physically larger than SD cards, these tend to be used by professional photographers in high-end cameras, due to their high speeds. Kingston Technology has a range of compact flash cards.

Flash: A type of memory that takes the form of a chip, making it similar in appearance to the chips on a RAM module. However, flash retains its data even without power. Different types of flash are used for various purposes, such as in thumb drives, memory cards and SSDs.

MMC: MultiMediaCards look almost identical to SD cards. In fact they fit into the same slot. Most devices that are compatible with SD cards can use MMC cards too.

NAND: NAND flash architecture was introduced by Toshiba in 1989. These memories are accessed much like block devices such as hard disks or memory cards. NAND is best suited to systems requiring high capacity data storage. This type of flash architecture offers higher densities and larger capacities at lower cost with faster erase, sequential write, and sequential read speeds, sacrificing the random-access and execute in place advantage of the NOR architecture.

NOR: NOR flash is a non-volatile memory that can hold the stored data even when the power is out. It also allows random data access, and provides fast reading and processing of data, which first made it ideal for code storage. With the increased use of mobile devices like cellular phone, PDA, digital camera, portable game consoles and MP3P, NOR flash is more widely used not only for code storage but also for data storage. It is also used in home appliances such as HDTV, DVD, Router, and GPS, and industrial and automotive uses are on the rise as well.

SD (Secure Digital): A type of memory card used in a large number of cameras and some camcorders. Comes in varying sizes from 8MB up to 2GB and has various speed grades. Faster cards allow capable cameras to take pictures more quickly. Also look out for miniSD and microSD – smaller sized cards designed for mobile phones and other slim devices.

A microSDHC card and its full-size adapter

SD Class x: SD and SDHC cards often come with a speed class rating. The class number refers to the guaranteed write speed, so SD Class 4 cards can write at 4MB/s. In digital photography terms, the number of photos per second depends on the resolution of the camera and its compression settings, but 4MB/s is roughly enough for one photo per second on a 10 megapixel camera.

SDHC: The higher capacity variant of SD, supporting capacities up to 32GB. Modern digital cameras often support SDHC, allowing more, higher resolution photos to be taken, along with HD video.

SDXC (Secure Digital Extended Capacity): The next-generation SDXC memory card specification dramatically improves consumers’ digital lifestyles by increasing storage capacity from more than 32 GB up to 2 TB. Its exFAT file system handles large volumes of data. SDXC’s extended capacity will provide more portable storage and speed, which are often required to support new features in consumer electronic devices, mobile devices and industrial devices. SD and SDHC cards will be backwards compatible with SDXC readers, but SDXC cards will not work with readers and devices that are not specifically designed for this new technology.

Transfer rate: The speed at which data can be transferred to/from a device. Read and write rates often differ. Sequential and random rates are often quoted, the former referring to operations that occur in order, the latter to utilising random locations across the device.

USB flash drives (Can also be referred to as a USB stick): A device that’s about as big as a thumb, making for easy, portable storage. Many flash drives can hold more data than CDs and even DVDs, and are more convenient to carry around, making them perfect for getting files between home and the office.

x-speeds: A way of rating speeds The value of X = 150 KB per second

We’ll update this glossary of terms as appropriate, and if you want a memory term explaining, please leave a comment!