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Explanatory Dictionary - DEF





DDR - Double Data Rate

DDR refers to a specification of SDRAM memory, DDR can transfer data at double the rate of normal SDRAM. It achieves this by transferring data twice per clock cycle, once on the rising edge and once on the falling edge of the cycle.

DIMM - Dual Inline Memory Module

DIMM refers to a type of memory module commonly used in modern PCs and Laptops.

DIMMS have a 64-bit data path and are widely used in PCs with 64-bit processors as they don't need to be doubled up unlike SIMMS.

The dual inline part refers to the way the chips are mounted on the module.

They come in either a 144 pin or 168 pin package, the 144 pin module is commonly used in laptops and the 168 pin modules are used in most modern PC motherboards.

Directory - Folder

A directory and folder are exactly the same thing, windows refers to them as folders but you will often come across them being called directories. Directories/folders allow information to be stored in your computer in a more convenient way making it easier to organise your files.

Directories/folders can be created, renamed and deleted much like files, it is good practise to create these directories/folders and keep your files in them as this helps keep your hard drive organised.

Disk Drive - Drives

Refers to a device that is used to read and write data using read/write heads from magnetic disk like devices. Floppy disk drive refers to the device at the front of the computer, floppy disks are inexpensive and are very handy for keeping small files backed up.

Hard disk drive refers to a device inside the computer where the bulk of the information is stored, the amount of data these can store vary, they range from 1Gb (in older machines) right up to 60Gb and beyond.

DLL - Dynamic Link Library

DLL refers to a type of file that is stored either locally or remotely and is a collection of commands and/or data which can be shared by different programs on the same platform.

Typical DLL files contain commands and/or data that are common to a certain task, for instance Windows has many DLL files built-in which other programs access and utilise. A common example of this is spool32.dll which is used for printing control within Windows 95/98 by other applications.

The one time you may become aware of DLL files is when your computer crashes and you are presented with a message such as an "invalid page fault".

The errors associated with DLL files are beyond the scope of this page, however, DLL files can be updated and most of the time a problem can be solved by updating the DLL file in question.

DMA - Direct Memory Access

This can be thought of as a channel or line that is used by devices in the computer to access the memory (RAM) without having to utilise the CPU. It works by allowing the I/O controller that has been previously instructed to transfer a block of data (the size depending on the system) to or from the memory to temporarily control the memory itself by returning the memory address of the data, it can control the memory for as many clock cycles as is required for the process. This system can significantly reduce the workload on the CPU.

Domain Name - DNS

A domain name is a unique name that is used to identify and locate computers on a network (including the internet), it can be used for websites and/or email addresses. For instance this website's domain name is www.helpwithpcs.com.

All machines connected to the internet have their own IP Address, domain names are just an easier way to access a certain machine, for instance if you had to remember IP Addresses instead of domain names it would be cumbersome.

DNS - Domain Name Server

When you type a domain name into your browser the name is looked up on what is called a domain name server, this server (or servers) points the browser to the IP Address of the machine that is listed under that domain name.

DOS - Disk Operating System

This is a system that software uses to utilise the disk drives in your computer. See also MS-DOS.

IBM® first created DOS® for the series 700 computers years ago, then Microsoft® developed their own version called MS-DOS®, over the years DOS has become outdated due to it's limited capabilities, although Windows® still shipped with MS-DOS® until the recent XP version.

DPI - Dots Per Inch

This is a measurement commonly used to describe the quality of printers and scanners, it refers to how many pixels per square inch that it is able to print/scan. The higher the DPI the smoother the quality of the image will be when either printed or scanned.

Printers and scanners both come with the ability (software driven) to alter their respective DPI, this can be useful if, for instance, you wanted to print out something on draft to save ink, you could lower the DPI of your printer and therefore the quality of the copy.

DRAM - Dynamic Random Access Memory

A type of memory (RAM) widely used in today's PCs. DRAM works differently to SDRAM as it needs to be refreshed to continue holding the data, this means a slight loss of speed as the memory refreshes itself with a pulse of current to each of its cells.

ECC - Error Correcting Code

Refers to a type of Memory (RAM) that automatically checks for errors as the data is passed through.

EDO Memory - Extended Data Ouput

Refers to a type of Memory (DRAM) that can simultaneously request the next block of data as it sends a block of data to the processor.

EIDE - Enhanced Integrated Drive Electronics

EIDE refers to an interface standard developed by Western Digital, since around the end of 1994 EIDE controllers have been widely used in the PC industry surpassing the earlier IDE standard due to its faster data transfer rates.

The interface controls storage devices like hard drives, CD ROM drives, and CD Writers.

Seagate introduced their own implementation of the EIDE standard and is commonly known as Fast ATA.

Typical EIDE transfer rates are up to 16.6 MBps, the newer Ultra ATA standard which is a variation of EIDE but developed by Seagate can reach data transfer rates of up to 33 MBps.

Email - Electronic Mail

This is a system used by computers to send and receive messages over the internet, when you send an email and likewise when someone sends you an email, the message will remain on the server (your email providers computer) until it is read and deleted, in other words you don't have to be connected to the internet to read an email unlike chat.

EPROM - Erasable Programmable Read Only Memory

Refers to a type of ROM that can be erased using an ultra violet light and then reprogrammed using a PROM Programmer. These chips have a small transparent area on the top, this is where the UV light is directed to clear the contents, they come in various different packages which make them very versatile. The ROM will retain the data until it is exposed again to an ultra violet light, it is normal practise to cover the small transparent area to avoid any potential data loss.

Ethernet - Networking

Refers to a standard of the LAN system, Ethernet supports up to 10Mbps per second transfer, a newer implementation of the Ethernet specification 100 Base-T supports up to 100Mbps.

The latest standard (Gigabit Ethernet) can support up to 1000Mbps (1 Gigabit).

Ethernets are common place in offices where file/device sharing is required.

FAT - File Allocation Table

FAT (File Allocation Table) refers to a data table that holds information about how and where files are stored on any one partition (for simplicity think of a partition as all the files on your hard drive).

For example, a single file on your hard drive may not be stored in one place, the file could be split up and stored in several different (physical) places (this is called fragmentation), the FAT keeps a record of where the different parts of the file are stored.

The FAT system does not duplicate critical data (as opposed to NTFS) so if a critical sector is lost then it can mean the loss of all data within the partition.

FAT16 was used in the first releases of Windows 95.

FAT32 is used by Windows 95 (later releases), Windows 98/98se and supported by Windows XP.

Firewall - Firewall protection

Refers to a security program which protects your computer from un-authorised access through a network and/or the Internet.

These are very important especially if your computer is connected directly to the Internet for long periods of time.

Freeware

This is software that is free, and as long as you can put up with the occasional advert there are some programs/utilities out there that are very useful. There are numerous sites on the internet that have huge collections of freeware, one we use is www.shareware.com.

FTP - File Transfer Protocol

One of the TCP/IP protocols used for transferring files across TCP/IP connections. The protocol manages the physical transfer of the file along with the representation of the file on both machines involved in the transfer. To upload or download files via FTP you need an FTP program such as Cute FTP.